CA1258327A - Driving method for optical modulation device - Google Patents
Driving method for optical modulation deviceInfo
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- CA1258327A CA1258327A CA000472482A CA472482A CA1258327A CA 1258327 A CA1258327 A CA 1258327A CA 000472482 A CA000472482 A CA 000472482A CA 472482 A CA472482 A CA 472482A CA 1258327 A CA1258327 A CA 1258327A
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Abstract
ABSTRACT OF THE DISCLOSURE
A driving method for an optical modulation device comprising matrix picture elements each formed at intersecting points of scanning lines and data lines between which a bistable optical modulation material represented by a ferroelectric liquid crsytal is interposed. The driving method comprises an erasure step of applying a voltage signal orienting the optical modulation material to the first stable state between the scanning and data lines, at all or a part of the matrix picture elements, and a writing step of sequentially applying a scanning selection signal to the scanning lines and applying an infor-mation orientation signal orienting the optical modulation material to the second stable state to the data lines in phase with the scanning selection signal.
A driving method for an optical modulation device comprising matrix picture elements each formed at intersecting points of scanning lines and data lines between which a bistable optical modulation material represented by a ferroelectric liquid crsytal is interposed. The driving method comprises an erasure step of applying a voltage signal orienting the optical modulation material to the first stable state between the scanning and data lines, at all or a part of the matrix picture elements, and a writing step of sequentially applying a scanning selection signal to the scanning lines and applying an infor-mation orientation signal orienting the optical modulation material to the second stable state to the data lines in phase with the scanning selection signal.
Description
58~ 7 DRIVING METHOD FOR OPTICAL MODULATION DEVICE
BAC~GROUND OF THE INVENTION
The present invention relates to a method of driving an optical modulation device, e.g., a liquid crystal device, and more particularly to a time-sharing driving method for an optical modulation device, e.g., a display device, an optical shutter array, etc.
Hitherto, liquid crystal display devices are well known, which comprise scanning lines (or elec-trodes) and data lines (or electrodes) arranged in a matrix manner, and a liquid crystal compound is filled between the lines to form a plurality of picture elements thereby to display images or information.
These display devices employ a time-sharing driving method which comprises the steps of selectively apply-ing scanning selection signals sequentially and cyclically to the scanning lines, and, in parallel therewith selectively applying predetermined informa-tion signals to the group of signal electrodes in synchronism with the scanning selection signals.
However, these display devices and the driving method therefor have a serious drawback as will be described below.
Namely, the drawback is that it is difficult to obtain a high density of picture elements or a ~2'~8;~ 7 large image area. Because of relatively high response speed and low power dissipation, among prior art liquid crystals, most of liquid crystals which have been put into practice as display devices are TN
(twisted nematic) type liquid crystals, as shown in "Voltage-Dependent Optical Activity of a Twisted Nematic Liquid Crystal" by M. Schadt and W. Helfrich, Applied Physics Letters Vol. 18, No. 4 (Feb. 15, 1971) pp. 127-128. In the liquid crystals of this type, molecules of nematic liquid crystal which show positive dielectric anisotropy under no application of an electric field form a structure twisted in the thick-ness direction of liquid crystal layers (helical structure), and molecules of these liquid crystals are aligned or oriented parallel to each other in the surfaces of both electrodes. On the other hand, nematic liquid crystals which show positive dielectric anisotropy under application of an electric field are oriented or aligned in the direction of the electric field. Thus, they can cause optical modulation. When display devices of a matrix electrode arrangement are designed using liquid crystals of this type, a voltage higher than a threshold level required for aligning liquid crystal molecules in the direction perpendicular to electrode surfaces is applied to areas (selected points) where scanning lines and data lines are selected at a time, whereas a voltage is not applied _3~ S8~2~
to areas (non-selected points) where scanning lines and data lines are not selected and, accordingly, the liquid crystal molecules are stably aligned parallel to the electrode surfaces. When linear polarizers arranged in a cross-nicol relationship, i.e., with their polarizing axes being substantially perpendicular to each other, are arranged on the upper and lower sides of a liquid crystal cell thus formed, a light does not transmit at selected points while it trans-mits at non-selected points. Thus, the liquid crystal cell can function as an image device.
However, when a matrix electrode structure is constituted, a certain electric field is applied to regions where scanning lines are selected and data lines are not selected or regions where scanning lines are not selected and data lines are selected (which regions are so called "half-selected points"). If the difference between a voltage applied to the selected points and a voltage applied to the half-selected points is sufficiently large, and a voltage threshold level required for allowing liquid crystal molecules to be aligned or oriented perpendicular to an electric field is set to a value therebetween, the display device normally operates. However, in fact, according as the number (N) of scanning lines increases, a time (duty ratio) during which an effective electric field is applied to one selected point when a whole image _4_ ~2S8;~7 area (corresponding to one frame) is scanned decreases with a ratio of 1/N. For this reason, the larger the number of scanning lines are, the smaller is the voltage difference as an effective value applied to a selected point and non-selected points when scanning is repeatedly effected. As a result, this leads to unavoidable drawbacks of lowering of image contrast or occurrence of crosstalk. These phenomena result in problems that cannot be essentially avoided, which ~ f~pr o_~
apopar when a liquid crystal not having bistability (which shows a stable state where liquid crystal mole-cules are oriented or aligned in a horizontal direction with respect to electrode surfaces, but are oriented in a vertical direction only when an electric field is effectively applied) is driven, i.e., repeatedly scanned, by making use of time storage effect. To overcome these drawbacks, the voltage averaging method, the two-frequency driving method, the multiple matrix method, etc., has already been proposed. However, any method is not sufficient to overcome the above-mentioned drawbacks. As a result, it is the present state that the development of large image area or high packaging density in respect to display elements is delayed because of the fact that it is difficult to sufficient-ly increase the number of scannin~ lines.
Meanwhile, turning to the field of a printer,as means for obtaining a hard copy in response to input 5 ~'~S8~7 electric signals, a Laser seam Printer (LBP) providing electric image signals to electrophotographic charging member in the form of lights is the most excellent in view of density of a picture element and a printing speed.
However, the LBP has drawbacks as follows:
1) It becomes large in apparatus size.
BAC~GROUND OF THE INVENTION
The present invention relates to a method of driving an optical modulation device, e.g., a liquid crystal device, and more particularly to a time-sharing driving method for an optical modulation device, e.g., a display device, an optical shutter array, etc.
Hitherto, liquid crystal display devices are well known, which comprise scanning lines (or elec-trodes) and data lines (or electrodes) arranged in a matrix manner, and a liquid crystal compound is filled between the lines to form a plurality of picture elements thereby to display images or information.
These display devices employ a time-sharing driving method which comprises the steps of selectively apply-ing scanning selection signals sequentially and cyclically to the scanning lines, and, in parallel therewith selectively applying predetermined informa-tion signals to the group of signal electrodes in synchronism with the scanning selection signals.
However, these display devices and the driving method therefor have a serious drawback as will be described below.
Namely, the drawback is that it is difficult to obtain a high density of picture elements or a ~2'~8;~ 7 large image area. Because of relatively high response speed and low power dissipation, among prior art liquid crystals, most of liquid crystals which have been put into practice as display devices are TN
(twisted nematic) type liquid crystals, as shown in "Voltage-Dependent Optical Activity of a Twisted Nematic Liquid Crystal" by M. Schadt and W. Helfrich, Applied Physics Letters Vol. 18, No. 4 (Feb. 15, 1971) pp. 127-128. In the liquid crystals of this type, molecules of nematic liquid crystal which show positive dielectric anisotropy under no application of an electric field form a structure twisted in the thick-ness direction of liquid crystal layers (helical structure), and molecules of these liquid crystals are aligned or oriented parallel to each other in the surfaces of both electrodes. On the other hand, nematic liquid crystals which show positive dielectric anisotropy under application of an electric field are oriented or aligned in the direction of the electric field. Thus, they can cause optical modulation. When display devices of a matrix electrode arrangement are designed using liquid crystals of this type, a voltage higher than a threshold level required for aligning liquid crystal molecules in the direction perpendicular to electrode surfaces is applied to areas (selected points) where scanning lines and data lines are selected at a time, whereas a voltage is not applied _3~ S8~2~
to areas (non-selected points) where scanning lines and data lines are not selected and, accordingly, the liquid crystal molecules are stably aligned parallel to the electrode surfaces. When linear polarizers arranged in a cross-nicol relationship, i.e., with their polarizing axes being substantially perpendicular to each other, are arranged on the upper and lower sides of a liquid crystal cell thus formed, a light does not transmit at selected points while it trans-mits at non-selected points. Thus, the liquid crystal cell can function as an image device.
However, when a matrix electrode structure is constituted, a certain electric field is applied to regions where scanning lines are selected and data lines are not selected or regions where scanning lines are not selected and data lines are selected (which regions are so called "half-selected points"). If the difference between a voltage applied to the selected points and a voltage applied to the half-selected points is sufficiently large, and a voltage threshold level required for allowing liquid crystal molecules to be aligned or oriented perpendicular to an electric field is set to a value therebetween, the display device normally operates. However, in fact, according as the number (N) of scanning lines increases, a time (duty ratio) during which an effective electric field is applied to one selected point when a whole image _4_ ~2S8;~7 area (corresponding to one frame) is scanned decreases with a ratio of 1/N. For this reason, the larger the number of scanning lines are, the smaller is the voltage difference as an effective value applied to a selected point and non-selected points when scanning is repeatedly effected. As a result, this leads to unavoidable drawbacks of lowering of image contrast or occurrence of crosstalk. These phenomena result in problems that cannot be essentially avoided, which ~ f~pr o_~
apopar when a liquid crystal not having bistability (which shows a stable state where liquid crystal mole-cules are oriented or aligned in a horizontal direction with respect to electrode surfaces, but are oriented in a vertical direction only when an electric field is effectively applied) is driven, i.e., repeatedly scanned, by making use of time storage effect. To overcome these drawbacks, the voltage averaging method, the two-frequency driving method, the multiple matrix method, etc., has already been proposed. However, any method is not sufficient to overcome the above-mentioned drawbacks. As a result, it is the present state that the development of large image area or high packaging density in respect to display elements is delayed because of the fact that it is difficult to sufficient-ly increase the number of scannin~ lines.
Meanwhile, turning to the field of a printer,as means for obtaining a hard copy in response to input 5 ~'~S8~7 electric signals, a Laser seam Printer (LBP) providing electric image signals to electrophotographic charging member in the form of lights is the most excellent in view of density of a picture element and a printing speed.
However, the LBP has drawbacks as follows:
1) It becomes large in apparatus size.
2) It has high speed mechanically movable parts such as a polygon scanner, resulting in noise and requirement for strict mechanical precision, etc.
In order to eliminate drawbacks stated above, a liquid crystal shutter-array is proposed as a device for changing electric signals to optical signals.
When picture element signals are provided with a liquid crystal shutter-array, however, 2000 signal generators are required, for instance, for writing picture element signals into a length of 200 mm in a ratio of 10 dots/mm. Accordingly, in order to independently feed signals to respective signal generators, lead lines for feeding electric signals are required to be, provided to all the respective signal generators, and the production has become difficult.
In view of the above, another attempt is made to apply one line of image signals in a time-sharing manner with signal generators divided into a plurality of lines.
1;~58:~7 With this attempt, signal feeding electrodes can be common to the plurality of signal generators, thereby enabling a remarkable decrease in the number of lead wires.
However, if the number (N) of lines is increased while using a liquid crystal showing no bistability, as is usually practiced, the signal "ON" time is substantially reduced to l/N. This results in the problems that quantity of light reacting a photoconductive member is decreased, and cross talk occurs.
SUMMARY OF THE INVENTION
The present invention seeks to provide a novel method of driving an optical modulation device, particularly a liquid crystal device, which addresses the abovementioned drawbacks encountered with prior art liquid crystal display devices or liquid crystal optical shutters as discussed above.
According to the invention, there is provided a driving method for an optical modulation device having a plurality of picture elements arranged in a matrix and comprising scanning lines, data lines spaced apart from and intersecting with the scanning lines, and a chiral smectic liquid crystal assuming a first orientation state or a second orientation state depending on the direction of an electric field applied thereto interposed between the scanning lines and the data lines, each of the intersections between the scanning lines and the data lines forming one of said plurality of picture elements; said driving method comprising an erasure step wherein a voltage exceeding a first threshold voltage of the chiral smectic liquid crystal for causing the first orientation state of the chiral smectic liquid crystal is applied to the intersections of the scanning lines and the data lines; a writing step wherein a scanning selection signal comprising 1258:~27 a voltage phase of one polarity and a voltage phase of the other polarity with respect to the voltage of a non-selected scanning line is applied to a selected scanning line, an information selection signal providing a voltage exceeding a second threshold voltage of the chiral smectic liquid crystal for causing the second orientation state of the chiral smectic liquid crystal, in combination with the voltage phase of one polarity of the scanning selection signal is applied to a selected data line, an information lo non-selection signal, providing a voltage between the first and second threshold voltages of the chiral smectic liquid crystal in combination with the voltage phase of one polarity of the scanning selection signal, is applied to other data lines, and an auxiliary signal for preventing inversion of the orientation states of the chiral smectic liquid crystal in combination with the voltage phase of the other polarity of the scanning selection signal i applied to the data lines.
These and further aspects of the present invention as set forth above and in the appended claims will become more apparent upon consideration of the following description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1 and 2 are schematic perspective views illustrating the basic operation principle of a liquid crystal device used in the present invention;
Figure 3A is a plan view of an electrode arrangement used in the present invention:
Figures 3B(a) - (d) illustrate waveforms of electric signals applied to electrodes;
. :
8~ 7 Figures 3C(a) - (d) illustrata voltage waveforms applied to picture elements:
Figures 4A and 4B, in combination, illustrate voltage waveforms applied in time series;
Figures 5A(a) - (d) illustrate waveforms of electric signals applied to electrodes in a different example;
Figures 5B(a) - (d) illustrate voltage waveforms applied to picture elements in the different example;
Figures 6A to lOA in combination with Figures 6B
to lOB, respectively, illustrate different examples of voltage waveforms applied in time series;
Figures llA and llD are plan views respectively showing an electrode arrangement used in further embodiments of the driving method according to the present invention;
Figures llB(a) - (d) illustrate waveforms of electric signals applied to electrodes;
Figures llC(a) - (d) illustrate voltage waveforms applied to picture elements;
Figures 12A to 15A in combination with Figures 12B to 15B, respectively, illustrate still further examples of voltage waveforms applied in time series;
Figure 16A is a plan view of an electrode arrangement in a further embodiment of the driving method according to the present invention;
,i ~Z58;~'~7 Figures 16B(a) -(d) illustrate waveforms of electric signals applied to electrodes in this further embodiment;
Figures 16C(a) - (d) illustrate voltage waveforms in this further embodiment; and Figures 17A and 17B in combination show voltage waveforms applied in time series in this further embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
10 As an optical modulation material used in a driving method according to the present invention, a material which shows either a first optically stable state or a second optically stable state depending upon an electric field applied thereto, i.e., has bistability with respect to the applied electric field, .....
-10~ 58~ 7 particularly a liquid crystal havin~ the above-mentioned property, may be used.
Preferable liquid crystals having bistability which can be used in the driving method according to the present invention are chiral smectic C (SmC*)- or H (SmH*)-phase liquid crystals having ferroelectricity.
In addition, liquid crystals showing chiral smectic I phase (SmI*), J phase (SmJ*), G phase (SmG*), F phase (SmF*) or K phase (SmK*) may also be used. These ferroelectric liquid crystals are described in, e.g., "LE JOURNAL DE PHYSIQUE LETTERS" 36 ~L-69), 1975 "Ferroelectric Liquid Crystals"; "Applied Physics Letters" 36 (11) 1980, "Submicro Second Bistable Electrooptic Switching in Liquid Crystals", "Solid State Physics" 16 (141), 1981 "Liquid Crystal", etc.
Ferroelectric liquid crystals disclosed in these publi-cations may be used in the present invention.
More particularly, examples of ferroelectric liquid crystal compound usable in the method according to the present invention include decyloxybenzylidene-p'-amino-2-methylbutyl cinnamate (DOBAMBC), hexyloxy-benzylidene-p'-amino-2-chloropropyl cinnamate (HOBACPC), 4-o-(2-methyl)-butylresorcilidene-4'-octylaniline (MBRA8), etc.
When a device is constituted using these materials, the device may be supported with a block of copper, etc., in which a heater is embedded in --ll--12S~ 7 order to realize a temperature condition where the liquid crystal compounds assume a smectic phase.
Referring to Figure 1, there is schematically shown an example of a ferroelectric liquid crystal cell for explanation of the operation thereof.
Reference numerals 11 and lla denote base plates (glass plates) on which a transparent electrode of, e.g., In2O3, SnO2, ITO (Indium-Tin Oxide), etc., is disposed, respectively. A liquid crystal of an SmC*-or SmH*-phase in which liquid crystal molecular layers 12 are oriented perpendicular to surfaces of the glass plates is hermetically disposed therebetween. A full line 13 shows liquid crystal molecules. Each liquid crystal molecule 13 has a dipole moment (Pl) 14 in a direction perpendicular to the axis thereof. When a voltage higher than a certain threshold level is applied between electrodes formed on the base plates 11 and 11a, a helical structure of the liquid crystal molecule 13 is released and unwound to change the alignment direction of respective liquid crystal molecules 13 so that the dipolç moments (Pl) 14 are all directed in the direction of the electric field. The liquid crystal molecules 13 have an elongated shape and show refractive anisotropy between the long axis and the short axis thereof. Accordingly, it is easily under-stood that then, for instance, polarizers arranged in a cross nicol relationship, i.e., with their polarizing -12- i~583~'~
directions crossing each other, are disposed on the upper and the lower surfaces of the glass plates, the liquid crystal cell thus arranyed functions as a liquid crystal optical modulation device, of which optical characteristics vary depending upon the polarity of an applied voltage. Further, when the thickness of the liquid crystal cell is sufficiently thin ~e.g., 1 ~), the helical structure of the liquid crystal molecules is loosened even in the absence of an electric field whereby the dipole moment assumes either of the two states, i.e., P in an upper direc-tion 24 or Pa in a lower direction 24a as shown in Figure 2. When electric field E or Ea higher than a certain threshold level and different from each other in polarity as shown in Figure 2 is applied to a cell having the above-mentioned characteristics, the dipole moment is directed either in the upper direction 24 or in the lower direction 24a depending on the vector of the electric field E or Ea. In correspondence with this, the liquid crystal molecules are oriented in either of a first stable state 23 and a second stable state 23a.
When the above-mentioned ferroelectric liquid crystal is used as an optical modulation element, it is possible to obtain two advantages. First is that the response speed is quite fast. Second is that the orientation of the liquid crystal shows bistability.
The second advantage will be further explained with reference to Figure 2. When the electric field E is applied to the liquid crystal molecules, they are oriented in the first stable state 23. This state is kept stable even if the electric field is removed. On the other hand, when the electric field Ea of which direction is opposite to that of the electric field E is applied thereto, the liquid crystal molecules are oriented to the second stable state 23a, whereby the directions of molecules are changed. This state is also kept stable even if the electric field is removed. Further, as long as the magnitude of the electric field E being applied is not above a certain threshold value, the liquid crystal molecules are placed in the respective orientation states. In order to effectively realize high response speed and bistabi-lity, it is preferable that the thickness of the cell is as thin as possible and generally 0.5 to 20 ~, particularly 1 to 5 ~. A liquid crystal electro-optical device having a matrix electrode structure in which the ferroelectric liquid crystal of this kind is used is proposed, e.g., in the specification of U.S. Patent No.
4367924 by Clark and Lagerwall.
Figure 3A schematically shows a cell 31 having picture elements arranged in a matrix which comprise scanning lines (scanning electrodes), data lines ,~
-14- 1258;~'~7 (signal electrodes) and a bistable optical modulation material interposed therebetween. Reference numeral 32 denotes scanning lines and reference numeral 33 denotes data lines. For the brevity of explanation, a case where two state signals of "white" and "black" are displayed is explained. It is assumed that hatched picture elements correspond to "black" and the other picture elements correspond to "white" in Figure 3A.
First, in order to make a picture uniformly "white"
(this step is called an "erasure step"), the bistable optical modulation material may be uniformly oriented to the first stable state. This can be effected by applying a predetermined voltage pulse signal (e.g., voltage: +2Vo, time width: ~t) to all the scanning lines and applying a predetermined pulse signal (e.g., -V0, ~t) to all the data lines. In the erasure step, an electric signal of polarity opposite to that of a scanning selection signal in the writing step described hereinbelow is applied to the scanning lines, and an electric signal of a polarity opposite to that of an information selec~ion signal (writing signal) in the writing step is applied to the data lines, in phase with each other.
Figures 3B(a) and 3B(b) show an electric signal (scanning selection signal) applied to a selected scanning line and an electric signal (scanning non-selection signal) applied to the other scanning lines (non-selected scanning lines), respectively. Figures 3B(c) and 3B(d) show an electric signal (information selection signal; V0 applied at phase T1) applied to a selected (referred to as "black") data line and an electric signal (information non-selection signal;
-V0 at phase Tl) applied to a non-selected (referred to as "white"~ data line, respectively. In the Figures 3B(a) - 3B(d), the abscissa represents time, and the ordinate a voltage, respectively. T1 and T2 in the figures represent a phase for applying an information signal (and a scanning signal) and a phase for apply-ing an auxiliary signal. This example shows a case where Tl = T2 = ~t.
The scanning lines 32 are selected sequentially.
It is assumed herein that a threshold voltage for providing the first stable state (white) of the bist-able liquid crystal at an application time of ~t be -Vth2, and a threshold voltage for providing the second stable state at an application time of ~t be Vth1.
Then, the electric signal applied to the selected scanning line comprises voltages of -2Vo at phase (time) T1 and o at phase (time) T2 as shown in Figure 3Bta). The other scanning lines are placed in grounded condition as shown in Figure 3B(b) and the electric signal is o. On the other hand, the electric signal - applied to the selected data line comprises V0 at `"` 12583~7 phase T1 and -V0 at phase T2 as shown in Figure 3B(c), and the electric signal applied to the non-selected data line comprises -V0 at phase T1 and +V0 at phase T2 as shown in Figure 3s(d)~ In this instance, the voltage V0 is set to a desired value which satisfies V0 < Vth1 ~ 3Vo and -V0 > Vth2 Voltage waveforms applied to respective picture elements when the above-mentioned electric signals are given are shown in Figures 3C. Figures 3C(a) and 3C~b) show voltage waveforms applied to picture elements where "black" and "white" are displayed, respectively, on the selected scanning line. Figures 3C(c) and 3C(d) respectively show voltage waveforms applied to picture elements on the non-selected scanning lines.
At phase T1, on the scanning line to which a scanning selection signal -2Vo is applied, an informa-tion signal ~V0 is applied to a picture element where "black" is to be displayed and, therefore, a voltage 3Vo exceeding the threshold voltage Vth1 is applied to the picture element, where the bistable liquid crystal is oriented to the second optically stable state.
Thus, the picture element is written in "black" (writ-ing step). On the same scanning line, the voltage applied to picture elements where "white" is to be displayed is a voltage V0 which does not exceed the threshold voltage Vth1, and accordingly the picture element remains in the first optically stable state, thus displaying "white".
On the other hand, on the non-selected scannin~
lines, the voltage applied to all the picture elements is +V or 0, each not exceeding the threshold voltage.
Accordingly, the liquid crystal at the respective picture elements retains its orientation which has been obtained when the picture elements have been last scanned. In other words, after the whole picture elements have been oriented to one optically stable state ("white"), when one scannina line is selected, signals are written in one line of picture elements at the first phase T1 and the written signal or display states are retained even after steps for writing one frame is finished.
Figure 4(combination of Figures 4A and 4B~
shows an example of the above-mentioned driving signals in time series. S1 to S5 represent electric signals applied to scanning lines; I1 and I3 represent electric signals applied to data lines; and A1 and C1 represent voltage waveforms applied to picture elements A1 and C1, respectively, shown in Figure 3A.
Microscopic mechanism of switching due to electric field of a ferroelectric liquid crystal having bistability has not been fully clarified. Generally speaking, however, the ferroelectric liquid crystal can retain its stable state semi-permanently, if it has been switched or oriented to the stable state by 12583;~7 application of a strong electric field for a predetermined time and is left standing under absolutely no electric field. However, when a reverse polarity electric field is applied to the liquid crystal for a long period of time, even if the electric field is such a weak field (corresponding to a voltage below Vth in the previous example) that the stable state of the liquid crystal is not switched in a writing interval, the liquid crystal may eventually change from one stable state to the other, so that correct display or modulation of information cannot be accomplished. We have found that the tendency to such switching or reversal of oriented states under long term application of a weak electric field is affected by the material used for and roughness of a base plate contacting the liquid crystal and the kind of the liquid crystal, but have not determined the effects quantitatively. We have confirmed a tendency for monoaxial treatment of the base plate such as rubbing or oblique or tilted vapour deposition of SiO, etc., increases the liability of the abovementioned reversal of oriented states. The tendency is more manifest at higher temperatures than at lower temperatures.
In any case, we have found it advisable, in order to accomplish correct display or modulation of information that a unidirectional electric field is prevented from being applied to the liquid crystal material for a prolonged period.
The phase T2 in the driving method described i8 provided for obviating a situation where a unidirectional weak electric field is continuously applied. For this purpose, as shown in Figures 3B(c) and 3B(d), a signal with a polarity opposite to that of the information signal (Figure 3B(c) corresponds to ~blackN, Figure 3B(d) to "whiteN) applied at phase Tl is applied to the data line at phase T2. In a case where a pattern as shown in Figure ..
- 19 - lZ58;~7 3A is displayed by a driving method not having such a phase T2, picture element Al is made "black" on scanning of the scanning electrode Sl, but it is highly possible that the picture element Al will be switched at some time to "white" because an electric signal or voltage of -VO is continuously applied to the signal electrode Il during the scanning of the remaining scanning electrodes S2 etc. and this voltage is continuously applied to the picture element Al .
The whole picture is first uniformly rendered "white", and then ~black~ is written into picture elements corresponding to information at the first phase Tl. In this example, the voltage for writing "black" at phase Tl is 3Vo and the application time is ~t. The voltage applied to the respective picture elements except at the scanning time is I +VO I at .....
B
-20- ~2583'~7 maximum, and the longest time during which the maximum voltage is 2~t is shown at 40 in Figure 4B. The severest condition is imposed when the information signals succeed in the order of white ~ white ~ black and the second "white" signal is applied at the scanning time. Even then, the application time is 4~t which is rather short and does not cause crosstalk at all, whereby a displayed information is retained semipermanently after the scanning of the whole picture is once completed. For this reason, a refreshing step as required in a display device using a TN liquid crystal having no bistability is not required at all.
The optimum length of the second phase T2 depends on the magnitude of the voltage applied to the data line. When a voltage having a polarity opposite to that of the information signal is applied, it is preferred that the time length is shorter for a larger voltage and longer for a shorter voltage. When the time is longer, it follows that a longer time is required for scanning the whole picture. Therefore, T2 is preferably set to satisfy T2 ~ Tl.
Figures 5 and 6 show a driving mode according to the present invention. Figures 5B(a) and 5B(b) show voltages applied to picture elements corre-sponding to "black" and "white", respectively, on aselected scanning line. Figures 5B(c) and 5B(d) show voltages applied to picture elements on a non-selected ~, -21- 1Z58:~2~7 scanning line and on a data line to which "black" or '`white" information signals are applied. Figure 6 (combination of Figures 6A and 6B) illustrates these signals applied in time series.
S Figure 7 (combination of Figures 7A and 7B) illustrates another embodiment of the erasure step than the one explained with reference to Figure 4.
Thus, in this example, the polarities of electric signals applied to scanning lines and data lines in the erasure step are made opposite to those of the scanning selection signals and information selection signals in the writing step. The voltage V0 is also set to a value satisfying the relationships of V0 < Vthl <3Vo and -V0 > Vth2 In the embodiment shown in Figure 7, in the erasure step ~t, an electric signal of 2Vo is applied to the scanning lines at a time and, in phase with the electric signal, a signal of -V0 with a polarity opposite to that of the electric signal is applied to the data lines. In the next writing step, signals similar to writing signals explained with reference to Figures 3 and 4 are applied to the scanning lines and data lines.
Figure 8 (combination of Figures 8A and 8B) and Figure 9 (combination of Figures 9A and 9B) respectively show examples of driving modes in time series. In these driving ............................
X
-22- 125~
modes, a voltage value V0 is so set that the threshold voltage for changing orientations for a p~lse width ~t is placed between ¦V0l and 2¦Vo¦.
In Figure 8 (Figures 8A and 8B), an electric signal of +V0 is applied to the scanning lines and, in phase therewith, an electric signal of _vO ;c ~nnlied to the data lines for erasing a picture. Immediately thereafter and subsequently, in the writing step, scanning signals of Sl, S2, ...., each of _vO, are se~uentially applied and, in phase with these scanning signals, information signals, each of +V0, are applied to data lines, whereby writing is carried out.
Figures 8 and 9 respectively show examples where no auxiliary signal is involved, whereas Figure 10 (combination of Figures lOA and lOB) shows an example where an auxiliary signal is used. Voltage values in respective driving pulses are shown in the figure. In the example of Figure 10, electric signals applied to scanning lines and data lines in the erasure step have polarities respectively opposite to those applied in the writing step, have magnitudes in terms of absolute values smaller (2/3 vo)than those of the latter and have larger pulse widths (2Qt) than those of the latter. This erasure mode is effective in a case where the threshold voltage depends on pulse widths and a threshold voltage Vth ~ for a width of 2~t satisfies a relationship of Vth2~t < 4/3 V0.
` ~258327 Figure 11 (inclusive of Figures llA, llB and llC) and Figure 12 ~combination of Figures 12A and l2s) illustrate a driving mode for an optical modulation device comprising:
a partial erasure step wherein electric signals are applied to selected scanning lines among the scanning lines and selected data lines; the selected scanning lines and selected data lines constituting a new image area where a new image is to be written, and the electric signals applied to the selected scanning lines and selected data lines having polarities opposite to those of a scanning selection signal and an information selection signal applied to the respective lines for writing images; whereby the optical modulation material constituting the new image area is oriented to the first stable state and an image written in a previous writing step is partially erased; and a partial writing step wherein a scanning selection signal is applied to the selected scanning lines and an information signal for orienting the optical modulation material to the second stable step is applied to the selected data lines corresponding to information giving the new image.
This driving mode will be explained with reference to Figure 11.
-2~ 8~327 Figure llA schematically shows a cell 111 having picture elements arranged in a matrix which comprise scanning lines (scanning electrodes), data lines (signal electrodes) and a bistable optical modulation S material interposed therebetween. Reference numeral 112 denotes data lines. For the brevity of exnlana-tion, a case where two state signals of "white" and "black'` are displayed is explained. It is assumed that h~tched picture elements corresn~nd to '`hl~k"
and the other picture elements correspond to "white"
in Figure 3A. First, in order to make a picture uniformly "white" (this step is called an "erasu,re step"), the bistable optical modulation material may be uniformly oriented to the first stable state. This can be effected by applying a predetermined voltage pulse signal (e.g., voltage: +2Vo, time width : Qt) to all the scanning lines and applying a predetermined pulse signal (e.g., -V0, Qt~ to all the data lines.
In the erasure step, an electric signal of a polarity opposite to that of a scanning selection signal in the writing step described hereinbelow is applied to the scanning lines, and an electric signal of a polarity opposite to that of an information selection signal (writing signal) in the writing step is applied to the data line, in phase with each other.
Figure llB(a) and llB(b) show an electric signal (scanning selection signal) applied to a selected scanning line and an electric signal (scanning non-selection signal) applied to the other scanning lines (nonselected scanning lines), respectively. Figures llB(c) and llB(d) show an electric signal (information selection signal V0 applied at phase Tl) applied to a selected ~referred to as "black") data line and an electric signal (information non-selection signal;
-V0 at phase Tl) applied to a non-selected (referred to as "white") data line, respectively. In the Figure llB(a) - llB(d), the abscissa represents time, and the ordinate a voltage, respectively. T1 and T2 in the figures represent a phase for applying an information signal (and scanning signal) and a phase for applying an auxiliary signal. This example shows a case where Tl 2 The scanning lines 112 are selected sequential-ly. It is assumed herein that a threshold voltage for providing the first stable state (white) of the bistable liquid crystal at an application time of ~t be -Vth2, and a threshold voltage for providing the second stable state at an application time of ~t be Vthl. Then, the electric signal applied to the selected scanning line comprises voltages of -2Vo at phase (time) Tl and 0 at phase (time) T2 as shown in Figure llB(a). The other scanning lines are placed ~ qrc~ d~d ¦~ in ~r~wndod condition as shown in Figure llB(b) and the electric signal is 0. On the other hand, the -2G- l~S8~27 electric signal applied to the selected data line comprises V0 at phase Tl and -V0 at phase T2 as shown in Figure llB(c), and the electric signal applied to the nonselected data line comprises -V0 at phase T
and +V0 at phase T2 as shown in Figure llB(d). In this instance, the voltage V0 is set to a desired value which satisfies V0 < Vth1 < 3Vo a 0 th2 > - 3Vo ' Voltage waveforms applied to rcspective picture elements when the above mentioned electric signals are given are shown in Figures llC. Figures llC(a) and llC(b) show voltage waveforms applied to picture elements where "black" and "white" are displayed, respectively, on the selected scanning line. Figures llC(c) and llC(d) respectively show voltage waveforms applied to picture elements on the nonselected scanning lines.
At phase Tl, on the scanning line to which a scanning selection signal -2Vo is applied, an information signal +V0 is applied to a picture element where "black" is to be displayed and, therefore, a voltage 3Vo exceeding the threshold voltage Vthl is applied to the picture element, where the bistable liquid crystal is oriented to the second optically stable state. Thus, the picture element is written in "black" (writing step). On the same scanning line, the voltage applied to picture elements where "white"
~25832~
is to be displayed is a voltage V0 which does not exceed the threshold voltage Vthl, and accordingly the picture element remains in the first optically stable state, thus displaying "white".
On the other hand, on the nonselected scanning lines, the voltage applied to all the picture elements is +V or 0, each not exceeding the threshold voltage.
Accordingly, the li~uid crystal at the respective picture elements retains its orientation which has been obtained when the picture elements have been last scanned. In other words, after the whole picture elements have been oriented to one optically stable state ("white"), when one scanning line is selected, signals are written in one line of picture elements at the first phase Tl and the written signal or display states are retained even after steps for writing one frame is finished.
Figure llA shows an example of a picture thus formed through the erasure step and the writing step. Figure llD shows an example of a picture obtained by partially rewriting the picture shown in Figure llA. This example shown in Figure llD illus-trates a case where an X-Y region or area formed by scanning lines X and data lines Y is intended to be rewritten. For this purpose, an electric signal (e.g., 2Vo shown in Figure 12) having a polarity opposite to that of a scanning selection signal -i.'.258~
-2~-(e.g., -2Vo in Figure 12) applied in the previous writing step is applied at a time or sequentially to scanning lines S1, S2 and S3 corresponding to the new image region (X-Y region) to be rewritten. On the other hand, an electric signal (e.g., -V0 on line Il in Figure 12) having a polarity opposite to that of an information selection signal (e.g., v0 on I1 in Figure 12) is applied to data lines I1 and I2 corresponding to the new image region. Thus, only a part (e.g., X-Y region) of one picture can be erased (Partial Erasure Step).
The writing in the partially erased region (X-Y region) is then effected by applying the same procedure as in the writing step, i.e., by applying an lS information selection signal (~V0) and an information non-selection signal (-V0) corresponding to predeter-mined rewriting image information to the data lines for the partially erased region in phase with a scanning selection signal (-2Vo).
On the other hand, an electric signal below the threshold vol~age of the ferroelectric liquid crystal is applied to the picture elements in the non-rewriting region (i.e., Xa~Y, Xa-Ya and X~Ya regions) so that the writing state of each picture element in the non-rewriting region is retaine~.
More specifically, in the partial erasure step, an electric signal (e.g., V0 on I3 in Figure 12) i~.58:~2'7 having the same polarity as an electric signal (e.g., 2Vo in Figure 12) applied to the scanning signal in the erasure step is applied to the data lines not constitut-ing the rewriting region (x-Y region). Further, in the partial writing step, an electric signal (e.g., -V0 on I3 in Figure 12) having the same polarity as a scanning selection signal (e.g., -2Vo on S1, S2 and S3 in Figure 12) is applied to the data lines not constituting the rewriting region (X-Y region) in phase with the selec-tion scanning signal. On the other hand, the potential of the scanning lines not constituting the rewriting region is held at a base potential (e.g., 0 volt).
The above explained driving signals are shown in time series in Figure 12 (combination of Figures 15 12A and 12B). S1 - S5 indicate electric signals ap-plied to scanning signals; I1 and I3 indicate elec-tric signals aplied to data lines; and A2, C2 and D2 indicate waveforms applied to picture elements A2, C2 and D2 shown in Figures llA and llD.
A rewriting region can be designated by a cursor.
Figure 13 (combination of Figures 13A and 13B) and Figure 14 (combination of Figures 14A and 14B) show further examples of driving modes. In these driving modes, V0 is set to such a value that the threshold voltage for changing orientations for a pulse width of ~t is placed .~, - 3n 1258~'327 between ¦V0l and ¦2Vo¦.
In the example shown in Figure 13 ~Figure 13A
and Figure 13B), an electric signal of +V0 is applied to the scanning lines and, in parallel therewith, an electric signal of -V0 is applied to the data lines for erasing a picture. Immediately thereafter, in the writing step, scanning signals S1, S2 ...., each of -V0, are sequentially applied and, in phase with these scanning signals, information signals, e~ch of +V0, are applied to data lines, whereby a picture as shown in Figure llA is written in.
Next, in the partial erasure step, an electric signal of -2Vo is applied to the picture elements which have been written in the previous step in the 5 X-Y region shown in Figure llD, whereby the picture th ~ s ~ ~ ~, elements are erased at ~ timé. (This example of one time erasure is shown in Figure 13. However, successive erasure is also possible by applying an electric signal of V0 successively to scanning lines as a scanning selection signal). Then, electric signals corresponding to new image information are applied to the X-Y region whereby the X-Y region is written as shown in Figure llD.
Figures 13 and 14 respectively show examples where no auxiliary signal is involved, whereas Figure 15 (combination of Figures 15A and 15B) shows an example where an auxiliary signal is used. Voltage -31- 125832~
values in respective driving pulses are shown in the figure. In the example of Figure 15, electric signals applied to scanning lines and data lines in the erasure step have polarities respectively opposite to those applied in the writing step, have magnitudes in terms of absolute values smaller (2/3 V0) than those of the latter and have larger pulse widths (2~t) than those of the latter. This erasure mode is effective in a case where the threshold voltage depends on pulse widths and a threshold voltage Vth2Qt for a width of 2~t satisfies a relationship of Vth < 4/3 V0.
In the partial erasure step, an electric signal of -4/3 V0 is applied to effect partial erasure.
In the next partial writing step, a new image is written in the X-Y region.
Figure 16 (inclusive of Figures 16A, 16B and 16C) and Figure 17 (combination of Figures 17A and 17B) illustrate another driving mode for an optical modula-tion device comprising: a writing step comprising a first phase wherein a voltage orienting the bistable optical modulation material to the first stable state is applied to picture elements on selected scanning lines among said plurality of picture elements, and a second phase wherein a voltage orienting the bistable optical modulation material to the second stable state is applied to a selected picture element among the picture elements on the selected scanning -32~ 8:~'7 lines to write in the selected picture element, and a step of applying an alternating current to the written selected picture element.
A further preferred example of this driving mode is used for driving a liquid crystal device which comprises scanning lines sequentially and periodically selected based on scanning signals, data lines facing the scanning lines and selected based on predetermined information signals, and a bistable liquid crystal assuming a first stable state or a second stable state depending on an electric field applied thereto interposed between the scanning lines and data lines. The liquid crystal device is driven by applying to a selected scanning line an electric signal comprising a first phase t1 providing one direction of an electric field by which the liquid crystal is oriented to the first stable state regard-less of an electric signal applied to signal electrodes and a second phase t1 having an auxiliary voltage assisting reorientation to the second stable state of the liquid crystal corresponding to electric signals applied to data lines, and a third step or phase t3 of applying to data lines an electric signal having a voltage polarity opposite to that of the electric signal applied at the phase t2 based on predetermined information.
A preferred embodiment according to this ~ode 1;~58327 is explained with reference to Figure 16.
Figure 16A schematically shows a cell 16 having picture elements arranged in a matrix which comprise scanning lines (scanning electrodes), data lines (signal electrodes) and a ferroelectric liquid crystal interposed therebetween. Reference numeral 162 denotes data lines. For the brevitv ~f exnl ana-tion, a case where two state signals of "white" and "black" are displayed is explained. It is assumed that hatched picture elements correspond to "black"
and the other picture elements correspond to "white"
in Figure 16A.
Figures 16B(a) and 16B(b) show an electric signal (scanning selection signal) applied to a selected scanning line and an electric signal (scanning non-selection signal) applied to the other scanning lines (nonselected scanning lines), respec-tively. Figures 16B(c) and 16B(d) show an electric signal (information selection signal) applied to a selected (referred to as "black") data line and an electric signal (information non-selection signal) applied to a non-selected (referred to as "white") data line, respectively. In the Figures 16B(a) -16B(d), the abscissa represents time, and the ordinate a voltage, respectively. T1, T2 and T3 in the writing step represent first, second and third phases, respec-tively. This example shows a case where T1 = T2 = T3.
1;~5~3Z 7 It is assumed herein that a threshold voltage for providing the first stable state (white) of the bistable liquid crystal for an application time of ~t be -Vth2, and a threshold voltage for providing the second stable state for an application time of ~t be Vthl. Then, the electric signal applied to the selected scanning line comprises voltages of 3Vo at phase (time) Tl, -2Vo at phase (time) T2 and 0 at phase (time) T3 as shown in Figure 16B(a). The other scan-ning lines are placed in grounded condition as shownin Figure 16B(b) and the electric signal is 0. On the other hand, the electric signal applied to the selected data line comprises 0 at phase Tl, V0 at phase T2 and -V0 at phase T2 as shown in Figure 16B(c), and the electric signal applied to the nonselected data line comprises 0 at phase T1, -V0 at phase T2 and +V0 at phase T3 as shown in Figure 16B(d). In this instance, the voltage V0 is set to a desired value which satisfies V0 < Vth1 < 3Vo and -V0 ~ -Vth2 ~ -3Vo-Voltage waveforms applied to respective picture elements when the above mentioned electric signals are given are shown in Figures 16C. Figur~s 16C(a) and 16C(b) show voltage waveforms applied to picture elements where "black" and "white" are displayed, respectively, on the selected scanning line. Figures 16C(c) and 16C(d) respectively show voltage waveforms applied to picture elements on the _35_ 1~258;~27 nonselected scanning lines.
As shown in Figure 16C, a voltage -3Vo exceeding the threshold voltage -Vth2 is applied to all the picture elements on the selected scanning line at phase Tl, whereby these picture elements are once rendered white. In the second phase T2, a voltage 3Vo exceeding the threshold voltage Vth1 ic ~pplied to the picture elements which are to be displayed as "black", whereby the other optically stable state ("black") is attained. Further, the voltage applied to the picture elements which are to be displayed as "white" is V0 not exceeding the threshold voltage, whreby the same optically stable state is maintained.
On the other hand, on the nonselected scanning lines, the voltage applied to all the picture elements is +V or 0, each not exceeding the threshold voltage.
Accordingly the liquid crystal at tha respective picture elements retains its orientation which has been obtained when the picture elements have been last scanned. In other words, when a scanning line is selected, all the picture elements on the scanning line is uniformly oriented to one optically stable state ("white") at phase Tl and selected picture elements are transformed into the other optically stable state ("black"), whereby one line is written.
The thus obtained signal or display state is retained even after writing steps for one frame is finished 125~327 -~6-and until subsequent scanning.
Figure 17 (combination of Figures 17A and 17B) shows an example of the above mentioned driving signals in time series. Sl to S5 represent electric signals applied to scanning lines; Il amd I3 represent electric signals applied to data lines; and A3 and C3 represent voltage waveforms applied to picture elements A3 and C3, respectively, shown in Figure 16A.
As has been described above, a reversal of orientation states (cross talk) can occur due to application of a weak electric field for a long period. In a preferred embodiment, however, the reversal of orientation states can be prevented by applying a signal capable of preventing continual application of a weak electric field in one direction.
Figures 16B(c) and 16B(d) illustrate a preferred embodiment for the above purpose wherein a signal having a polarity opposite to that of an information signal ("black" in Figure 16B(c) and "white" in Figure 16B(d)) applied to a data line at phase T2 is applied to the data line at phase T3 In a case where a pattern shown in Figure 16A is intended to be displayed, for example, by a driving method not having such phase T3, picture element A3 i~ made "black" on scanning of the scanning line Sl, but it is highly possible that the picture element A3 will be switched sometime to "white" because an electric signal or voltage of -V0 is continuously applied to the signal electrode Il during the steps for scanning of the scanning electrode S2 and so on and the voltage is continuously applied to the picture element A3 as it is.
The whole picture is once uniformly rendered "white" at the first phase Tl, and then "black" is written into picture elements corres2onding to information at the second phase T2 in the scanning.
In this example, the voltage for providing "white" at phase T1 is -3Vo and the application time is Qt.
Further, the voltage for writing "black" at phase T2 is 3Vo and the application time is also ~t. The voltage applied to the respective picture elements except at the scanning time is ¦+V0l to the maximum, and the longest time during which the maximum voltage is 2~t as shown at part 161 in Figure 17. Thus cross talk does not occur at all, whereby a displayed information is retained semipermanently after the scanning of the whole picture is once completed. For this reason, a refreshing step as required in a display device using a TN liquid crystal having no bistability is not required at all.
The optimum length of the third phase T3 depends on the magnitude of the voltage applied to the data line at this phase. When a voltage having a _3~ 5~327 polarity opposite to that of the information signal is applied, it is preferred that the time length is shorter for a larger voltage and longer for a shorter voltage. When the time is longer, it follows that a longer time is re~uired for scanning the whole picture.
Therefore, T3 is preferably set to satisfy T3 < T2.
The driving method according to the present invention can be widely applied in the field of optical shutters and display such as liquid crystal-optical shutters and liquid crystal TV sets.
Hereinbelow, the present invention will beexplained with reference to working examples.
Example 1 A pair of electrode plates each comprising a glass substrate and a transparent electrode pattern of ITO tIndium-Tin-Oxide) formed thereon were provided.
These electrodes were capable of giving a 500 x 500 matrix electrode structure. On the electrode pattern of one of the electrode plates was formed a polyimide film of about 300A in thickness by spin coating. The polyimide face of the electrode plate was rubbed with a roller about which a suede cloth was wound.
The electrode plate was bonded to the other electrode plate which was not coated with a polyimide film, thereby to form a cell having a gap of about 1.6~.
Into the cell was injected a ferroelectric crystal of decyloxybenzylidene-p'-amino-2-methylbutyl 12583~27 cinnamate (DOBAMBC) under hot-melting state, which was then gradually cooled to form a uniform monodomain of SmC phase.
The thus formed cell was held at a controlled temperature of 70C and driven by line-by-line scan-ning according to the driving mode explained with ref-erence to Figures 3 and 4 under the conditions of v0 =
10 volt, and T1 = T2 = ~t = 80 ~sec, whereby an ext-remely good image was obtained.
Example 2 Writing of image was conducted in the same manner as in Example 1 except that the driving mode shown in Figure 7 was used instead of the mode in Example 1, whereby a good image was obtained.
Example 3 Line-by-line scanning was carried out in the same manner as in Example 1 except that the driving waveforms shown in Figure 12 was used, whereby extremely good image was formed. Then, a part of the image was rewritten according to driving waveforms shown in Figure 12, whereby a good partially-rewritten image was obtained.
Example 4 Line-by line scanning was carrried out in the same manner as in Example 1 except that the waveforms shown in Figures 16 and 17 were used under the conditions of V0 = 10 volt, and T1=T2=T3=~t=50 ~sec, -1(. 125~ Z'~
~ wherebyJextremely good image was ~ormed.
In order to eliminate drawbacks stated above, a liquid crystal shutter-array is proposed as a device for changing electric signals to optical signals.
When picture element signals are provided with a liquid crystal shutter-array, however, 2000 signal generators are required, for instance, for writing picture element signals into a length of 200 mm in a ratio of 10 dots/mm. Accordingly, in order to independently feed signals to respective signal generators, lead lines for feeding electric signals are required to be, provided to all the respective signal generators, and the production has become difficult.
In view of the above, another attempt is made to apply one line of image signals in a time-sharing manner with signal generators divided into a plurality of lines.
1;~58:~7 With this attempt, signal feeding electrodes can be common to the plurality of signal generators, thereby enabling a remarkable decrease in the number of lead wires.
However, if the number (N) of lines is increased while using a liquid crystal showing no bistability, as is usually practiced, the signal "ON" time is substantially reduced to l/N. This results in the problems that quantity of light reacting a photoconductive member is decreased, and cross talk occurs.
SUMMARY OF THE INVENTION
The present invention seeks to provide a novel method of driving an optical modulation device, particularly a liquid crystal device, which addresses the abovementioned drawbacks encountered with prior art liquid crystal display devices or liquid crystal optical shutters as discussed above.
According to the invention, there is provided a driving method for an optical modulation device having a plurality of picture elements arranged in a matrix and comprising scanning lines, data lines spaced apart from and intersecting with the scanning lines, and a chiral smectic liquid crystal assuming a first orientation state or a second orientation state depending on the direction of an electric field applied thereto interposed between the scanning lines and the data lines, each of the intersections between the scanning lines and the data lines forming one of said plurality of picture elements; said driving method comprising an erasure step wherein a voltage exceeding a first threshold voltage of the chiral smectic liquid crystal for causing the first orientation state of the chiral smectic liquid crystal is applied to the intersections of the scanning lines and the data lines; a writing step wherein a scanning selection signal comprising 1258:~27 a voltage phase of one polarity and a voltage phase of the other polarity with respect to the voltage of a non-selected scanning line is applied to a selected scanning line, an information selection signal providing a voltage exceeding a second threshold voltage of the chiral smectic liquid crystal for causing the second orientation state of the chiral smectic liquid crystal, in combination with the voltage phase of one polarity of the scanning selection signal is applied to a selected data line, an information lo non-selection signal, providing a voltage between the first and second threshold voltages of the chiral smectic liquid crystal in combination with the voltage phase of one polarity of the scanning selection signal, is applied to other data lines, and an auxiliary signal for preventing inversion of the orientation states of the chiral smectic liquid crystal in combination with the voltage phase of the other polarity of the scanning selection signal i applied to the data lines.
These and further aspects of the present invention as set forth above and in the appended claims will become more apparent upon consideration of the following description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1 and 2 are schematic perspective views illustrating the basic operation principle of a liquid crystal device used in the present invention;
Figure 3A is a plan view of an electrode arrangement used in the present invention:
Figures 3B(a) - (d) illustrate waveforms of electric signals applied to electrodes;
. :
8~ 7 Figures 3C(a) - (d) illustrata voltage waveforms applied to picture elements:
Figures 4A and 4B, in combination, illustrate voltage waveforms applied in time series;
Figures 5A(a) - (d) illustrate waveforms of electric signals applied to electrodes in a different example;
Figures 5B(a) - (d) illustrate voltage waveforms applied to picture elements in the different example;
Figures 6A to lOA in combination with Figures 6B
to lOB, respectively, illustrate different examples of voltage waveforms applied in time series;
Figures llA and llD are plan views respectively showing an electrode arrangement used in further embodiments of the driving method according to the present invention;
Figures llB(a) - (d) illustrate waveforms of electric signals applied to electrodes;
Figures llC(a) - (d) illustrate voltage waveforms applied to picture elements;
Figures 12A to 15A in combination with Figures 12B to 15B, respectively, illustrate still further examples of voltage waveforms applied in time series;
Figure 16A is a plan view of an electrode arrangement in a further embodiment of the driving method according to the present invention;
,i ~Z58;~'~7 Figures 16B(a) -(d) illustrate waveforms of electric signals applied to electrodes in this further embodiment;
Figures 16C(a) - (d) illustrate voltage waveforms in this further embodiment; and Figures 17A and 17B in combination show voltage waveforms applied in time series in this further embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
10 As an optical modulation material used in a driving method according to the present invention, a material which shows either a first optically stable state or a second optically stable state depending upon an electric field applied thereto, i.e., has bistability with respect to the applied electric field, .....
-10~ 58~ 7 particularly a liquid crystal havin~ the above-mentioned property, may be used.
Preferable liquid crystals having bistability which can be used in the driving method according to the present invention are chiral smectic C (SmC*)- or H (SmH*)-phase liquid crystals having ferroelectricity.
In addition, liquid crystals showing chiral smectic I phase (SmI*), J phase (SmJ*), G phase (SmG*), F phase (SmF*) or K phase (SmK*) may also be used. These ferroelectric liquid crystals are described in, e.g., "LE JOURNAL DE PHYSIQUE LETTERS" 36 ~L-69), 1975 "Ferroelectric Liquid Crystals"; "Applied Physics Letters" 36 (11) 1980, "Submicro Second Bistable Electrooptic Switching in Liquid Crystals", "Solid State Physics" 16 (141), 1981 "Liquid Crystal", etc.
Ferroelectric liquid crystals disclosed in these publi-cations may be used in the present invention.
More particularly, examples of ferroelectric liquid crystal compound usable in the method according to the present invention include decyloxybenzylidene-p'-amino-2-methylbutyl cinnamate (DOBAMBC), hexyloxy-benzylidene-p'-amino-2-chloropropyl cinnamate (HOBACPC), 4-o-(2-methyl)-butylresorcilidene-4'-octylaniline (MBRA8), etc.
When a device is constituted using these materials, the device may be supported with a block of copper, etc., in which a heater is embedded in --ll--12S~ 7 order to realize a temperature condition where the liquid crystal compounds assume a smectic phase.
Referring to Figure 1, there is schematically shown an example of a ferroelectric liquid crystal cell for explanation of the operation thereof.
Reference numerals 11 and lla denote base plates (glass plates) on which a transparent electrode of, e.g., In2O3, SnO2, ITO (Indium-Tin Oxide), etc., is disposed, respectively. A liquid crystal of an SmC*-or SmH*-phase in which liquid crystal molecular layers 12 are oriented perpendicular to surfaces of the glass plates is hermetically disposed therebetween. A full line 13 shows liquid crystal molecules. Each liquid crystal molecule 13 has a dipole moment (Pl) 14 in a direction perpendicular to the axis thereof. When a voltage higher than a certain threshold level is applied between electrodes formed on the base plates 11 and 11a, a helical structure of the liquid crystal molecule 13 is released and unwound to change the alignment direction of respective liquid crystal molecules 13 so that the dipolç moments (Pl) 14 are all directed in the direction of the electric field. The liquid crystal molecules 13 have an elongated shape and show refractive anisotropy between the long axis and the short axis thereof. Accordingly, it is easily under-stood that then, for instance, polarizers arranged in a cross nicol relationship, i.e., with their polarizing -12- i~583~'~
directions crossing each other, are disposed on the upper and the lower surfaces of the glass plates, the liquid crystal cell thus arranyed functions as a liquid crystal optical modulation device, of which optical characteristics vary depending upon the polarity of an applied voltage. Further, when the thickness of the liquid crystal cell is sufficiently thin ~e.g., 1 ~), the helical structure of the liquid crystal molecules is loosened even in the absence of an electric field whereby the dipole moment assumes either of the two states, i.e., P in an upper direc-tion 24 or Pa in a lower direction 24a as shown in Figure 2. When electric field E or Ea higher than a certain threshold level and different from each other in polarity as shown in Figure 2 is applied to a cell having the above-mentioned characteristics, the dipole moment is directed either in the upper direction 24 or in the lower direction 24a depending on the vector of the electric field E or Ea. In correspondence with this, the liquid crystal molecules are oriented in either of a first stable state 23 and a second stable state 23a.
When the above-mentioned ferroelectric liquid crystal is used as an optical modulation element, it is possible to obtain two advantages. First is that the response speed is quite fast. Second is that the orientation of the liquid crystal shows bistability.
The second advantage will be further explained with reference to Figure 2. When the electric field E is applied to the liquid crystal molecules, they are oriented in the first stable state 23. This state is kept stable even if the electric field is removed. On the other hand, when the electric field Ea of which direction is opposite to that of the electric field E is applied thereto, the liquid crystal molecules are oriented to the second stable state 23a, whereby the directions of molecules are changed. This state is also kept stable even if the electric field is removed. Further, as long as the magnitude of the electric field E being applied is not above a certain threshold value, the liquid crystal molecules are placed in the respective orientation states. In order to effectively realize high response speed and bistabi-lity, it is preferable that the thickness of the cell is as thin as possible and generally 0.5 to 20 ~, particularly 1 to 5 ~. A liquid crystal electro-optical device having a matrix electrode structure in which the ferroelectric liquid crystal of this kind is used is proposed, e.g., in the specification of U.S. Patent No.
4367924 by Clark and Lagerwall.
Figure 3A schematically shows a cell 31 having picture elements arranged in a matrix which comprise scanning lines (scanning electrodes), data lines ,~
-14- 1258;~'~7 (signal electrodes) and a bistable optical modulation material interposed therebetween. Reference numeral 32 denotes scanning lines and reference numeral 33 denotes data lines. For the brevity of explanation, a case where two state signals of "white" and "black" are displayed is explained. It is assumed that hatched picture elements correspond to "black" and the other picture elements correspond to "white" in Figure 3A.
First, in order to make a picture uniformly "white"
(this step is called an "erasure step"), the bistable optical modulation material may be uniformly oriented to the first stable state. This can be effected by applying a predetermined voltage pulse signal (e.g., voltage: +2Vo, time width: ~t) to all the scanning lines and applying a predetermined pulse signal (e.g., -V0, ~t) to all the data lines. In the erasure step, an electric signal of polarity opposite to that of a scanning selection signal in the writing step described hereinbelow is applied to the scanning lines, and an electric signal of a polarity opposite to that of an information selec~ion signal (writing signal) in the writing step is applied to the data lines, in phase with each other.
Figures 3B(a) and 3B(b) show an electric signal (scanning selection signal) applied to a selected scanning line and an electric signal (scanning non-selection signal) applied to the other scanning lines (non-selected scanning lines), respectively. Figures 3B(c) and 3B(d) show an electric signal (information selection signal; V0 applied at phase T1) applied to a selected (referred to as "black") data line and an electric signal (information non-selection signal;
-V0 at phase Tl) applied to a non-selected (referred to as "white"~ data line, respectively. In the Figures 3B(a) - 3B(d), the abscissa represents time, and the ordinate a voltage, respectively. T1 and T2 in the figures represent a phase for applying an information signal (and a scanning signal) and a phase for apply-ing an auxiliary signal. This example shows a case where Tl = T2 = ~t.
The scanning lines 32 are selected sequentially.
It is assumed herein that a threshold voltage for providing the first stable state (white) of the bist-able liquid crystal at an application time of ~t be -Vth2, and a threshold voltage for providing the second stable state at an application time of ~t be Vth1.
Then, the electric signal applied to the selected scanning line comprises voltages of -2Vo at phase (time) T1 and o at phase (time) T2 as shown in Figure 3Bta). The other scanning lines are placed in grounded condition as shown in Figure 3B(b) and the electric signal is o. On the other hand, the electric signal - applied to the selected data line comprises V0 at `"` 12583~7 phase T1 and -V0 at phase T2 as shown in Figure 3B(c), and the electric signal applied to the non-selected data line comprises -V0 at phase T1 and +V0 at phase T2 as shown in Figure 3s(d)~ In this instance, the voltage V0 is set to a desired value which satisfies V0 < Vth1 ~ 3Vo and -V0 > Vth2 Voltage waveforms applied to respective picture elements when the above-mentioned electric signals are given are shown in Figures 3C. Figures 3C(a) and 3C~b) show voltage waveforms applied to picture elements where "black" and "white" are displayed, respectively, on the selected scanning line. Figures 3C(c) and 3C(d) respectively show voltage waveforms applied to picture elements on the non-selected scanning lines.
At phase T1, on the scanning line to which a scanning selection signal -2Vo is applied, an informa-tion signal ~V0 is applied to a picture element where "black" is to be displayed and, therefore, a voltage 3Vo exceeding the threshold voltage Vth1 is applied to the picture element, where the bistable liquid crystal is oriented to the second optically stable state.
Thus, the picture element is written in "black" (writ-ing step). On the same scanning line, the voltage applied to picture elements where "white" is to be displayed is a voltage V0 which does not exceed the threshold voltage Vth1, and accordingly the picture element remains in the first optically stable state, thus displaying "white".
On the other hand, on the non-selected scannin~
lines, the voltage applied to all the picture elements is +V or 0, each not exceeding the threshold voltage.
Accordingly, the liquid crystal at the respective picture elements retains its orientation which has been obtained when the picture elements have been last scanned. In other words, after the whole picture elements have been oriented to one optically stable state ("white"), when one scannina line is selected, signals are written in one line of picture elements at the first phase T1 and the written signal or display states are retained even after steps for writing one frame is finished.
Figure 4(combination of Figures 4A and 4B~
shows an example of the above-mentioned driving signals in time series. S1 to S5 represent electric signals applied to scanning lines; I1 and I3 represent electric signals applied to data lines; and A1 and C1 represent voltage waveforms applied to picture elements A1 and C1, respectively, shown in Figure 3A.
Microscopic mechanism of switching due to electric field of a ferroelectric liquid crystal having bistability has not been fully clarified. Generally speaking, however, the ferroelectric liquid crystal can retain its stable state semi-permanently, if it has been switched or oriented to the stable state by 12583;~7 application of a strong electric field for a predetermined time and is left standing under absolutely no electric field. However, when a reverse polarity electric field is applied to the liquid crystal for a long period of time, even if the electric field is such a weak field (corresponding to a voltage below Vth in the previous example) that the stable state of the liquid crystal is not switched in a writing interval, the liquid crystal may eventually change from one stable state to the other, so that correct display or modulation of information cannot be accomplished. We have found that the tendency to such switching or reversal of oriented states under long term application of a weak electric field is affected by the material used for and roughness of a base plate contacting the liquid crystal and the kind of the liquid crystal, but have not determined the effects quantitatively. We have confirmed a tendency for monoaxial treatment of the base plate such as rubbing or oblique or tilted vapour deposition of SiO, etc., increases the liability of the abovementioned reversal of oriented states. The tendency is more manifest at higher temperatures than at lower temperatures.
In any case, we have found it advisable, in order to accomplish correct display or modulation of information that a unidirectional electric field is prevented from being applied to the liquid crystal material for a prolonged period.
The phase T2 in the driving method described i8 provided for obviating a situation where a unidirectional weak electric field is continuously applied. For this purpose, as shown in Figures 3B(c) and 3B(d), a signal with a polarity opposite to that of the information signal (Figure 3B(c) corresponds to ~blackN, Figure 3B(d) to "whiteN) applied at phase Tl is applied to the data line at phase T2. In a case where a pattern as shown in Figure ..
- 19 - lZ58;~7 3A is displayed by a driving method not having such a phase T2, picture element Al is made "black" on scanning of the scanning electrode Sl, but it is highly possible that the picture element Al will be switched at some time to "white" because an electric signal or voltage of -VO is continuously applied to the signal electrode Il during the scanning of the remaining scanning electrodes S2 etc. and this voltage is continuously applied to the picture element Al .
The whole picture is first uniformly rendered "white", and then ~black~ is written into picture elements corresponding to information at the first phase Tl. In this example, the voltage for writing "black" at phase Tl is 3Vo and the application time is ~t. The voltage applied to the respective picture elements except at the scanning time is I +VO I at .....
B
-20- ~2583'~7 maximum, and the longest time during which the maximum voltage is 2~t is shown at 40 in Figure 4B. The severest condition is imposed when the information signals succeed in the order of white ~ white ~ black and the second "white" signal is applied at the scanning time. Even then, the application time is 4~t which is rather short and does not cause crosstalk at all, whereby a displayed information is retained semipermanently after the scanning of the whole picture is once completed. For this reason, a refreshing step as required in a display device using a TN liquid crystal having no bistability is not required at all.
The optimum length of the second phase T2 depends on the magnitude of the voltage applied to the data line. When a voltage having a polarity opposite to that of the information signal is applied, it is preferred that the time length is shorter for a larger voltage and longer for a shorter voltage. When the time is longer, it follows that a longer time is required for scanning the whole picture. Therefore, T2 is preferably set to satisfy T2 ~ Tl.
Figures 5 and 6 show a driving mode according to the present invention. Figures 5B(a) and 5B(b) show voltages applied to picture elements corre-sponding to "black" and "white", respectively, on aselected scanning line. Figures 5B(c) and 5B(d) show voltages applied to picture elements on a non-selected ~, -21- 1Z58:~2~7 scanning line and on a data line to which "black" or '`white" information signals are applied. Figure 6 (combination of Figures 6A and 6B) illustrates these signals applied in time series.
S Figure 7 (combination of Figures 7A and 7B) illustrates another embodiment of the erasure step than the one explained with reference to Figure 4.
Thus, in this example, the polarities of electric signals applied to scanning lines and data lines in the erasure step are made opposite to those of the scanning selection signals and information selection signals in the writing step. The voltage V0 is also set to a value satisfying the relationships of V0 < Vthl <3Vo and -V0 > Vth2 In the embodiment shown in Figure 7, in the erasure step ~t, an electric signal of 2Vo is applied to the scanning lines at a time and, in phase with the electric signal, a signal of -V0 with a polarity opposite to that of the electric signal is applied to the data lines. In the next writing step, signals similar to writing signals explained with reference to Figures 3 and 4 are applied to the scanning lines and data lines.
Figure 8 (combination of Figures 8A and 8B) and Figure 9 (combination of Figures 9A and 9B) respectively show examples of driving modes in time series. In these driving ............................
X
-22- 125~
modes, a voltage value V0 is so set that the threshold voltage for changing orientations for a p~lse width ~t is placed between ¦V0l and 2¦Vo¦.
In Figure 8 (Figures 8A and 8B), an electric signal of +V0 is applied to the scanning lines and, in phase therewith, an electric signal of _vO ;c ~nnlied to the data lines for erasing a picture. Immediately thereafter and subsequently, in the writing step, scanning signals of Sl, S2, ...., each of _vO, are se~uentially applied and, in phase with these scanning signals, information signals, each of +V0, are applied to data lines, whereby writing is carried out.
Figures 8 and 9 respectively show examples where no auxiliary signal is involved, whereas Figure 10 (combination of Figures lOA and lOB) shows an example where an auxiliary signal is used. Voltage values in respective driving pulses are shown in the figure. In the example of Figure 10, electric signals applied to scanning lines and data lines in the erasure step have polarities respectively opposite to those applied in the writing step, have magnitudes in terms of absolute values smaller (2/3 vo)than those of the latter and have larger pulse widths (2Qt) than those of the latter. This erasure mode is effective in a case where the threshold voltage depends on pulse widths and a threshold voltage Vth ~ for a width of 2~t satisfies a relationship of Vth2~t < 4/3 V0.
` ~258327 Figure 11 (inclusive of Figures llA, llB and llC) and Figure 12 ~combination of Figures 12A and l2s) illustrate a driving mode for an optical modulation device comprising:
a partial erasure step wherein electric signals are applied to selected scanning lines among the scanning lines and selected data lines; the selected scanning lines and selected data lines constituting a new image area where a new image is to be written, and the electric signals applied to the selected scanning lines and selected data lines having polarities opposite to those of a scanning selection signal and an information selection signal applied to the respective lines for writing images; whereby the optical modulation material constituting the new image area is oriented to the first stable state and an image written in a previous writing step is partially erased; and a partial writing step wherein a scanning selection signal is applied to the selected scanning lines and an information signal for orienting the optical modulation material to the second stable step is applied to the selected data lines corresponding to information giving the new image.
This driving mode will be explained with reference to Figure 11.
-2~ 8~327 Figure llA schematically shows a cell 111 having picture elements arranged in a matrix which comprise scanning lines (scanning electrodes), data lines (signal electrodes) and a bistable optical modulation S material interposed therebetween. Reference numeral 112 denotes data lines. For the brevity of exnlana-tion, a case where two state signals of "white" and "black'` are displayed is explained. It is assumed that h~tched picture elements corresn~nd to '`hl~k"
and the other picture elements correspond to "white"
in Figure 3A. First, in order to make a picture uniformly "white" (this step is called an "erasu,re step"), the bistable optical modulation material may be uniformly oriented to the first stable state. This can be effected by applying a predetermined voltage pulse signal (e.g., voltage: +2Vo, time width : Qt) to all the scanning lines and applying a predetermined pulse signal (e.g., -V0, Qt~ to all the data lines.
In the erasure step, an electric signal of a polarity opposite to that of a scanning selection signal in the writing step described hereinbelow is applied to the scanning lines, and an electric signal of a polarity opposite to that of an information selection signal (writing signal) in the writing step is applied to the data line, in phase with each other.
Figure llB(a) and llB(b) show an electric signal (scanning selection signal) applied to a selected scanning line and an electric signal (scanning non-selection signal) applied to the other scanning lines (nonselected scanning lines), respectively. Figures llB(c) and llB(d) show an electric signal (information selection signal V0 applied at phase Tl) applied to a selected ~referred to as "black") data line and an electric signal (information non-selection signal;
-V0 at phase Tl) applied to a non-selected (referred to as "white") data line, respectively. In the Figure llB(a) - llB(d), the abscissa represents time, and the ordinate a voltage, respectively. T1 and T2 in the figures represent a phase for applying an information signal (and scanning signal) and a phase for applying an auxiliary signal. This example shows a case where Tl 2 The scanning lines 112 are selected sequential-ly. It is assumed herein that a threshold voltage for providing the first stable state (white) of the bistable liquid crystal at an application time of ~t be -Vth2, and a threshold voltage for providing the second stable state at an application time of ~t be Vthl. Then, the electric signal applied to the selected scanning line comprises voltages of -2Vo at phase (time) Tl and 0 at phase (time) T2 as shown in Figure llB(a). The other scanning lines are placed ~ qrc~ d~d ¦~ in ~r~wndod condition as shown in Figure llB(b) and the electric signal is 0. On the other hand, the -2G- l~S8~27 electric signal applied to the selected data line comprises V0 at phase Tl and -V0 at phase T2 as shown in Figure llB(c), and the electric signal applied to the nonselected data line comprises -V0 at phase T
and +V0 at phase T2 as shown in Figure llB(d). In this instance, the voltage V0 is set to a desired value which satisfies V0 < Vth1 < 3Vo a 0 th2 > - 3Vo ' Voltage waveforms applied to rcspective picture elements when the above mentioned electric signals are given are shown in Figures llC. Figures llC(a) and llC(b) show voltage waveforms applied to picture elements where "black" and "white" are displayed, respectively, on the selected scanning line. Figures llC(c) and llC(d) respectively show voltage waveforms applied to picture elements on the nonselected scanning lines.
At phase Tl, on the scanning line to which a scanning selection signal -2Vo is applied, an information signal +V0 is applied to a picture element where "black" is to be displayed and, therefore, a voltage 3Vo exceeding the threshold voltage Vthl is applied to the picture element, where the bistable liquid crystal is oriented to the second optically stable state. Thus, the picture element is written in "black" (writing step). On the same scanning line, the voltage applied to picture elements where "white"
~25832~
is to be displayed is a voltage V0 which does not exceed the threshold voltage Vthl, and accordingly the picture element remains in the first optically stable state, thus displaying "white".
On the other hand, on the nonselected scanning lines, the voltage applied to all the picture elements is +V or 0, each not exceeding the threshold voltage.
Accordingly, the li~uid crystal at the respective picture elements retains its orientation which has been obtained when the picture elements have been last scanned. In other words, after the whole picture elements have been oriented to one optically stable state ("white"), when one scanning line is selected, signals are written in one line of picture elements at the first phase Tl and the written signal or display states are retained even after steps for writing one frame is finished.
Figure llA shows an example of a picture thus formed through the erasure step and the writing step. Figure llD shows an example of a picture obtained by partially rewriting the picture shown in Figure llA. This example shown in Figure llD illus-trates a case where an X-Y region or area formed by scanning lines X and data lines Y is intended to be rewritten. For this purpose, an electric signal (e.g., 2Vo shown in Figure 12) having a polarity opposite to that of a scanning selection signal -i.'.258~
-2~-(e.g., -2Vo in Figure 12) applied in the previous writing step is applied at a time or sequentially to scanning lines S1, S2 and S3 corresponding to the new image region (X-Y region) to be rewritten. On the other hand, an electric signal (e.g., -V0 on line Il in Figure 12) having a polarity opposite to that of an information selection signal (e.g., v0 on I1 in Figure 12) is applied to data lines I1 and I2 corresponding to the new image region. Thus, only a part (e.g., X-Y region) of one picture can be erased (Partial Erasure Step).
The writing in the partially erased region (X-Y region) is then effected by applying the same procedure as in the writing step, i.e., by applying an lS information selection signal (~V0) and an information non-selection signal (-V0) corresponding to predeter-mined rewriting image information to the data lines for the partially erased region in phase with a scanning selection signal (-2Vo).
On the other hand, an electric signal below the threshold vol~age of the ferroelectric liquid crystal is applied to the picture elements in the non-rewriting region (i.e., Xa~Y, Xa-Ya and X~Ya regions) so that the writing state of each picture element in the non-rewriting region is retaine~.
More specifically, in the partial erasure step, an electric signal (e.g., V0 on I3 in Figure 12) i~.58:~2'7 having the same polarity as an electric signal (e.g., 2Vo in Figure 12) applied to the scanning signal in the erasure step is applied to the data lines not constitut-ing the rewriting region (x-Y region). Further, in the partial writing step, an electric signal (e.g., -V0 on I3 in Figure 12) having the same polarity as a scanning selection signal (e.g., -2Vo on S1, S2 and S3 in Figure 12) is applied to the data lines not constituting the rewriting region (X-Y region) in phase with the selec-tion scanning signal. On the other hand, the potential of the scanning lines not constituting the rewriting region is held at a base potential (e.g., 0 volt).
The above explained driving signals are shown in time series in Figure 12 (combination of Figures 15 12A and 12B). S1 - S5 indicate electric signals ap-plied to scanning signals; I1 and I3 indicate elec-tric signals aplied to data lines; and A2, C2 and D2 indicate waveforms applied to picture elements A2, C2 and D2 shown in Figures llA and llD.
A rewriting region can be designated by a cursor.
Figure 13 (combination of Figures 13A and 13B) and Figure 14 (combination of Figures 14A and 14B) show further examples of driving modes. In these driving modes, V0 is set to such a value that the threshold voltage for changing orientations for a pulse width of ~t is placed .~, - 3n 1258~'327 between ¦V0l and ¦2Vo¦.
In the example shown in Figure 13 ~Figure 13A
and Figure 13B), an electric signal of +V0 is applied to the scanning lines and, in parallel therewith, an electric signal of -V0 is applied to the data lines for erasing a picture. Immediately thereafter, in the writing step, scanning signals S1, S2 ...., each of -V0, are sequentially applied and, in phase with these scanning signals, information signals, e~ch of +V0, are applied to data lines, whereby a picture as shown in Figure llA is written in.
Next, in the partial erasure step, an electric signal of -2Vo is applied to the picture elements which have been written in the previous step in the 5 X-Y region shown in Figure llD, whereby the picture th ~ s ~ ~ ~, elements are erased at ~ timé. (This example of one time erasure is shown in Figure 13. However, successive erasure is also possible by applying an electric signal of V0 successively to scanning lines as a scanning selection signal). Then, electric signals corresponding to new image information are applied to the X-Y region whereby the X-Y region is written as shown in Figure llD.
Figures 13 and 14 respectively show examples where no auxiliary signal is involved, whereas Figure 15 (combination of Figures 15A and 15B) shows an example where an auxiliary signal is used. Voltage -31- 125832~
values in respective driving pulses are shown in the figure. In the example of Figure 15, electric signals applied to scanning lines and data lines in the erasure step have polarities respectively opposite to those applied in the writing step, have magnitudes in terms of absolute values smaller (2/3 V0) than those of the latter and have larger pulse widths (2~t) than those of the latter. This erasure mode is effective in a case where the threshold voltage depends on pulse widths and a threshold voltage Vth2Qt for a width of 2~t satisfies a relationship of Vth < 4/3 V0.
In the partial erasure step, an electric signal of -4/3 V0 is applied to effect partial erasure.
In the next partial writing step, a new image is written in the X-Y region.
Figure 16 (inclusive of Figures 16A, 16B and 16C) and Figure 17 (combination of Figures 17A and 17B) illustrate another driving mode for an optical modula-tion device comprising: a writing step comprising a first phase wherein a voltage orienting the bistable optical modulation material to the first stable state is applied to picture elements on selected scanning lines among said plurality of picture elements, and a second phase wherein a voltage orienting the bistable optical modulation material to the second stable state is applied to a selected picture element among the picture elements on the selected scanning -32~ 8:~'7 lines to write in the selected picture element, and a step of applying an alternating current to the written selected picture element.
A further preferred example of this driving mode is used for driving a liquid crystal device which comprises scanning lines sequentially and periodically selected based on scanning signals, data lines facing the scanning lines and selected based on predetermined information signals, and a bistable liquid crystal assuming a first stable state or a second stable state depending on an electric field applied thereto interposed between the scanning lines and data lines. The liquid crystal device is driven by applying to a selected scanning line an electric signal comprising a first phase t1 providing one direction of an electric field by which the liquid crystal is oriented to the first stable state regard-less of an electric signal applied to signal electrodes and a second phase t1 having an auxiliary voltage assisting reorientation to the second stable state of the liquid crystal corresponding to electric signals applied to data lines, and a third step or phase t3 of applying to data lines an electric signal having a voltage polarity opposite to that of the electric signal applied at the phase t2 based on predetermined information.
A preferred embodiment according to this ~ode 1;~58327 is explained with reference to Figure 16.
Figure 16A schematically shows a cell 16 having picture elements arranged in a matrix which comprise scanning lines (scanning electrodes), data lines (signal electrodes) and a ferroelectric liquid crystal interposed therebetween. Reference numeral 162 denotes data lines. For the brevitv ~f exnl ana-tion, a case where two state signals of "white" and "black" are displayed is explained. It is assumed that hatched picture elements correspond to "black"
and the other picture elements correspond to "white"
in Figure 16A.
Figures 16B(a) and 16B(b) show an electric signal (scanning selection signal) applied to a selected scanning line and an electric signal (scanning non-selection signal) applied to the other scanning lines (nonselected scanning lines), respec-tively. Figures 16B(c) and 16B(d) show an electric signal (information selection signal) applied to a selected (referred to as "black") data line and an electric signal (information non-selection signal) applied to a non-selected (referred to as "white") data line, respectively. In the Figures 16B(a) -16B(d), the abscissa represents time, and the ordinate a voltage, respectively. T1, T2 and T3 in the writing step represent first, second and third phases, respec-tively. This example shows a case where T1 = T2 = T3.
1;~5~3Z 7 It is assumed herein that a threshold voltage for providing the first stable state (white) of the bistable liquid crystal for an application time of ~t be -Vth2, and a threshold voltage for providing the second stable state for an application time of ~t be Vthl. Then, the electric signal applied to the selected scanning line comprises voltages of 3Vo at phase (time) Tl, -2Vo at phase (time) T2 and 0 at phase (time) T3 as shown in Figure 16B(a). The other scan-ning lines are placed in grounded condition as shownin Figure 16B(b) and the electric signal is 0. On the other hand, the electric signal applied to the selected data line comprises 0 at phase Tl, V0 at phase T2 and -V0 at phase T2 as shown in Figure 16B(c), and the electric signal applied to the nonselected data line comprises 0 at phase T1, -V0 at phase T2 and +V0 at phase T3 as shown in Figure 16B(d). In this instance, the voltage V0 is set to a desired value which satisfies V0 < Vth1 < 3Vo and -V0 ~ -Vth2 ~ -3Vo-Voltage waveforms applied to respective picture elements when the above mentioned electric signals are given are shown in Figures 16C. Figur~s 16C(a) and 16C(b) show voltage waveforms applied to picture elements where "black" and "white" are displayed, respectively, on the selected scanning line. Figures 16C(c) and 16C(d) respectively show voltage waveforms applied to picture elements on the _35_ 1~258;~27 nonselected scanning lines.
As shown in Figure 16C, a voltage -3Vo exceeding the threshold voltage -Vth2 is applied to all the picture elements on the selected scanning line at phase Tl, whereby these picture elements are once rendered white. In the second phase T2, a voltage 3Vo exceeding the threshold voltage Vth1 ic ~pplied to the picture elements which are to be displayed as "black", whereby the other optically stable state ("black") is attained. Further, the voltage applied to the picture elements which are to be displayed as "white" is V0 not exceeding the threshold voltage, whreby the same optically stable state is maintained.
On the other hand, on the nonselected scanning lines, the voltage applied to all the picture elements is +V or 0, each not exceeding the threshold voltage.
Accordingly the liquid crystal at tha respective picture elements retains its orientation which has been obtained when the picture elements have been last scanned. In other words, when a scanning line is selected, all the picture elements on the scanning line is uniformly oriented to one optically stable state ("white") at phase Tl and selected picture elements are transformed into the other optically stable state ("black"), whereby one line is written.
The thus obtained signal or display state is retained even after writing steps for one frame is finished 125~327 -~6-and until subsequent scanning.
Figure 17 (combination of Figures 17A and 17B) shows an example of the above mentioned driving signals in time series. Sl to S5 represent electric signals applied to scanning lines; Il amd I3 represent electric signals applied to data lines; and A3 and C3 represent voltage waveforms applied to picture elements A3 and C3, respectively, shown in Figure 16A.
As has been described above, a reversal of orientation states (cross talk) can occur due to application of a weak electric field for a long period. In a preferred embodiment, however, the reversal of orientation states can be prevented by applying a signal capable of preventing continual application of a weak electric field in one direction.
Figures 16B(c) and 16B(d) illustrate a preferred embodiment for the above purpose wherein a signal having a polarity opposite to that of an information signal ("black" in Figure 16B(c) and "white" in Figure 16B(d)) applied to a data line at phase T2 is applied to the data line at phase T3 In a case where a pattern shown in Figure 16A is intended to be displayed, for example, by a driving method not having such phase T3, picture element A3 i~ made "black" on scanning of the scanning line Sl, but it is highly possible that the picture element A3 will be switched sometime to "white" because an electric signal or voltage of -V0 is continuously applied to the signal electrode Il during the steps for scanning of the scanning electrode S2 and so on and the voltage is continuously applied to the picture element A3 as it is.
The whole picture is once uniformly rendered "white" at the first phase Tl, and then "black" is written into picture elements corres2onding to information at the second phase T2 in the scanning.
In this example, the voltage for providing "white" at phase T1 is -3Vo and the application time is Qt.
Further, the voltage for writing "black" at phase T2 is 3Vo and the application time is also ~t. The voltage applied to the respective picture elements except at the scanning time is ¦+V0l to the maximum, and the longest time during which the maximum voltage is 2~t as shown at part 161 in Figure 17. Thus cross talk does not occur at all, whereby a displayed information is retained semipermanently after the scanning of the whole picture is once completed. For this reason, a refreshing step as required in a display device using a TN liquid crystal having no bistability is not required at all.
The optimum length of the third phase T3 depends on the magnitude of the voltage applied to the data line at this phase. When a voltage having a _3~ 5~327 polarity opposite to that of the information signal is applied, it is preferred that the time length is shorter for a larger voltage and longer for a shorter voltage. When the time is longer, it follows that a longer time is re~uired for scanning the whole picture.
Therefore, T3 is preferably set to satisfy T3 < T2.
The driving method according to the present invention can be widely applied in the field of optical shutters and display such as liquid crystal-optical shutters and liquid crystal TV sets.
Hereinbelow, the present invention will beexplained with reference to working examples.
Example 1 A pair of electrode plates each comprising a glass substrate and a transparent electrode pattern of ITO tIndium-Tin-Oxide) formed thereon were provided.
These electrodes were capable of giving a 500 x 500 matrix electrode structure. On the electrode pattern of one of the electrode plates was formed a polyimide film of about 300A in thickness by spin coating. The polyimide face of the electrode plate was rubbed with a roller about which a suede cloth was wound.
The electrode plate was bonded to the other electrode plate which was not coated with a polyimide film, thereby to form a cell having a gap of about 1.6~.
Into the cell was injected a ferroelectric crystal of decyloxybenzylidene-p'-amino-2-methylbutyl 12583~27 cinnamate (DOBAMBC) under hot-melting state, which was then gradually cooled to form a uniform monodomain of SmC phase.
The thus formed cell was held at a controlled temperature of 70C and driven by line-by-line scan-ning according to the driving mode explained with ref-erence to Figures 3 and 4 under the conditions of v0 =
10 volt, and T1 = T2 = ~t = 80 ~sec, whereby an ext-remely good image was obtained.
Example 2 Writing of image was conducted in the same manner as in Example 1 except that the driving mode shown in Figure 7 was used instead of the mode in Example 1, whereby a good image was obtained.
Example 3 Line-by-line scanning was carried out in the same manner as in Example 1 except that the driving waveforms shown in Figure 12 was used, whereby extremely good image was formed. Then, a part of the image was rewritten according to driving waveforms shown in Figure 12, whereby a good partially-rewritten image was obtained.
Example 4 Line-by line scanning was carrried out in the same manner as in Example 1 except that the waveforms shown in Figures 16 and 17 were used under the conditions of V0 = 10 volt, and T1=T2=T3=~t=50 ~sec, -1(. 125~ Z'~
~ wherebyJextremely good image was ~ormed.
Claims (73)
1. An optical modulation device comprising: a chiral smectic liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a chiral smectic liquid crystal disposed therebetween, and signal application means: said signal application means being arranged (i) to apply a scanning selection signal to a scanning electrode, said scanning selection signal comprising a voltage signal of one polarity and a voltage signal of the other polarity, with respect to the voltage level of a non-selected scanning electrode in a first phase and a second phase, respectively; (ii) to apply, in such a first phase, to the signal electrodes a voltage signal providing a voltage of one polarity exceeding a first threshold voltage of the chiral smectic liquid crystal in combination with the scanning selection signal; and (iii) to apply, in such a second phase, to at least one signal electrode selected from the signal electrodes a voltage signal providing a voltage of the other polarity exceeding a second threshold voltage of the chiral smectic liquid crystal in combination with the scanning selection signal and also providing a voltage between the first and second threshold voltage of the chiral smectic liquid crystal in combination with a voltage signal applied to the non-selected scanning electrode.
2. The optical modulation device according to Claim 1, wherein the scanning selection signal is sequentially applied to the scanning electrodes.
3. The optical modulation device according to Claim 1, wherein said voltage signal of one polarity and the other polarity are consecutive with respect to time.
4. The optical modulation device according to Claim 1, wherein said voltage of one polarity applied in the first phase and said voltage of the other polarity applied in the second phase have mutually different voltage amplitudes with respect to the voltage level of a scanning electrode when the scanning electrode is not selected.
5. An optical modulation device, comprising: a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween so as to provide a picture element at each intersection of the scanning electrodes and the signal electrodes, and signal application means for applying information signals to the signal electrodes in phase with scanning signals selectively applied to the scanning electrodes; said signal application means being arranged (a) to apply an information signal to a signal electrode to provide an orientation state of the ferroelectric liquid crystal at a picture element on a selected scanning electrode corresponding to that signal electrode and (b) in a period when the scanning electrode for that picture element becomes a non-selected scanning electrode, (i) to apply a voltage of one polarity to the picture element, and (ii) before the application time of said voltage of one polarity reaches a length of time beyond which said voltage of one polarity causes the inversion of the orientation state into another orientation state of the ferroelectric liquid crystal, to apply to the signal electrode corresponding to that picture element a voltage signal providing a zero voltage or a voltage of a polarity opposite to said one polarity to that picture element.
6. The optical modulation device according to Claim 5 wherein said voltage of one polarity and said zero voltage or said voltage of the other polarity alternate with time.
7. An optical modulation device, comprising; a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second stable states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels; and signal application means including means for defining a rewriting region and a non-rewriting region in the matrix of picture elements; means for applying a first writing voltage exceeding the first threshold level or a second writing voltage exceeding the second threshold level to selected picture elements in the rewriting region depending on given information, while applying a scanning signal sequentially to the scanning electrodes corresponding to the rewriting region;
means for applying a voltage between the first and second threshold levels to the picture elements in the non-rewriting region;
means for applying an information signal to a signal electrode to provide a stable state of the chiral smectic liquid crystal at a picture element on a selected scanning electrode; and means for, in a period when the picture element is placed on a non-selected scanning electrode, applying a voltage of one same polarity to the picture element, and before said voltage of one same polarity reaches a length of time beyond which said voltage of one same polarity causes the inversion of the stable state into another state of the chiral smectic liquid crystal, applying a polarity opposite to said one same polarity to the picture element.
means for applying a voltage between the first and second threshold levels to the picture elements in the non-rewriting region;
means for applying an information signal to a signal electrode to provide a stable state of the chiral smectic liquid crystal at a picture element on a selected scanning electrode; and means for, in a period when the picture element is placed on a non-selected scanning electrode, applying a voltage of one same polarity to the picture element, and before said voltage of one same polarity reaches a length of time beyond which said voltage of one same polarity causes the inversion of the stable state into another state of the chiral smectic liquid crystal, applying a polarity opposite to said one same polarity to the picture element.
8. The optical modulation device according to Claim 7 wherein a voltage signal providing said voltage of 0 or a polarity opposite to said one same polarity is applied to a signal electrode connected to the picture element.
9. The optical modulation device according to Claim 7 wherein said voltage of one same polarity and said voltage of 0 or the other polarity alternate with time.
10. An optical modulation device comprising: a chiral smectic liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a chiral smectic liquid crystal disposed therebetween, and signal application means; said signal application means being arranged (i) to apply a scanning selection signal to a scanning electrode, said scanning selection signal comprising a voltage signal of one polarity and a voltage signal of the other polarity, with respect to the voltage level of a non-selected scanning electrode in first phase and a second phase, respectively; (ii) to apply, in such a first phase, to at least one signal electrode a voltage signal providing a voltage of one polarity exceeding a first threshold voltage of the chiral smectic liquid crystal in combination with the scanning selection signal: and (iii) to apply, in such a second phase, to at least one signal electrode a voltage signal providing a voltage of the other polarity exceeding a second threshold voltage of the chiral smectic liquid crystal in combination with the scanning selection signal and also providing a voltage between the first and second threshold voltage of the chiral smectic liquid crystal in combination with a voltage signal applied to the non-selected scanning electrode.
11. The optical modulation device according to Claim 10, wherein the scanning selection signal is sequentially applied to the scanning electrodes.
12. A method of addressing a matrix array type liquid crystal display device with a ferro-electric liquid crystal layer whose pixels are defined by the areas of overlay between the members of a first set of electrodes on one side of the liquid crystal layer and the members of a second set of electrodes on the other side of the layer, and whose pixels exhibit optical properties when selectively operted to fully on and fully off states, wherein strobing pulses are applied serially to the members of the first set while data pulses are applied in parallel to the second set in order to address the cell line by line, and wherein the waveform of a data pulse is balanced bipolar and at last twice the duration of a strobing pulse, and wherein the balanced bipolar data pulse when applied to a non-addressed pixel in other than a fully on state or fully off state restores such pixel to its original condition at the end of the data pulse.
13. A method as claimed in Claim 12, wherein the duration of a data pulse is twice that of a strobing pulse.
14. A method as claimed in Claim 12, wherein a bipolar data pulse is one of positive and negative going in the first half of the pulse duration and the other of negative and positive going in the second half, and wherein the strobing pulses are unidirectional and always synchronized with one of the first and second halves of the data pulses.
15. A method as claimed in Claim 13, wherein a bipolar data pulse is one of positive and negative going in the first half of the pulse duration and the other of negative and positive going in the second half, and wherein the strobing pulses are unidirectional and always synchronized with one of the first and second halves of the data pulses.
16. A method as claimed in Claim 14, wherein prior to the addressing of the pixels associated with any particular member of the first set of electrodes these pixels are all erased by a blanking pulse applied to that member of the first set of electrodes, which blanking pulse is of opposite polarity to the strobing pulses that after the blanking induce a state change in the addressed pixels, and which is applied at or after the commencement of the bipolar data pulses used to address the pixels associated with the member of the first set of electrodes to which the strobing pulse is applied immediately preceding its application to that said particular member.
17. A method as claimed in Claim 15, wherein prior to the addressing of the pixels associated with any particular member of the first set of electrodes these pixels are all erased by a blanking pulse applied to that member of the first set of electrodes, which blanking pulse is of opposite polarity to the strobing pulses that after the blanking induce a state change in the addressed pixels, and which is applied at or after the commencement of the bipolar data pulses used to address the pixels associated with the member of the first set of electrodes to which the strobing pulse is applied immediately preceding its application to that said particular member.
18. A liquid crystal display apparatus comprising:
a plurality of scanning electrode means;
a plurality of signal electrode means positioned perpendicular to the scanning electrode means to form a matrix and enclosing a ferroelectric liquid crystal layer having a plurality of pixels in conjunction with the scanning electrode means;
first drive means for selecting and sequentially driving the scanning electrode means by applying write-in voltages thereto;
second drive means for driving the signal electrode means by applying voltages corresponding to display contents of the display apparatus in synchronism with the application of the write-in voltages; and, control means coupled to the first and second drive means, for controlling the first drive means so as to apply reset voltages to the respective pixels of the ferroelectric liquid crystal layer, whereby orientation of the liquid crystal's molecule is subjected to be constant before the selection of the scanning electrode means.
a plurality of scanning electrode means;
a plurality of signal electrode means positioned perpendicular to the scanning electrode means to form a matrix and enclosing a ferroelectric liquid crystal layer having a plurality of pixels in conjunction with the scanning electrode means;
first drive means for selecting and sequentially driving the scanning electrode means by applying write-in voltages thereto;
second drive means for driving the signal electrode means by applying voltages corresponding to display contents of the display apparatus in synchronism with the application of the write-in voltages; and, control means coupled to the first and second drive means, for controlling the first drive means so as to apply reset voltages to the respective pixels of the ferroelectric liquid crystal layer, whereby orientation of the liquid crystal's molecule is subjected to be constant before the selection of the scanning electrode means.
19. A liquid crystal display apparatus as claimed in Claim 18, wherein a drive period during which the reset voltage is being applied to a first scanning electrode of said scanning electrode means, is interposed between a first time instant at which a second scanning electrode is selected just before said selection of the first one, and a second time instant at which said first scanning electrode is selected.
20. A liquid crystal display apparatus as claimed in Claim 18, wherein a polarity of potential of the scanning electrode means which appears during the application of the reset voltages, is reversed with respect to the polarity of the write voltages.
21. A liquid crystal display device driven in a time sharing mode, comprising;
a pair of electrodes spaced apart from each other;
a ferroelectric liquid crystal layer disposed between the pair of electrodes such that the layer loses a spiral molecular alignment thereof to establish two bi-stable molecular alignments thereof; drive means connected between the pair of electrodes for applying an electric signal to the layer sufficient to change one of the two bistable molecular alignments to the other bi-stable molecular alignment and for applying an A.C. electric signal to the layer effective to hold the other bi-stable molecular alignments; and converting means for converting the two bi-stable molecular alignments to corresponding optical ON and OFF display states, respectively.
a pair of electrodes spaced apart from each other;
a ferroelectric liquid crystal layer disposed between the pair of electrodes such that the layer loses a spiral molecular alignment thereof to establish two bi-stable molecular alignments thereof; drive means connected between the pair of electrodes for applying an electric signal to the layer sufficient to change one of the two bistable molecular alignments to the other bi-stable molecular alignment and for applying an A.C. electric signal to the layer effective to hold the other bi-stable molecular alignments; and converting means for converting the two bi-stable molecular alignments to corresponding optical ON and OFF display states, respectively.
22. A liquid crystal display device as claimed in Claim 21; wherein the drive means includes means for adjusting the electric signal effective to change the bi-stable molecular alignments to compensate for changes in ambient temperature.
23. A liquid crystal display device as claimed in Claim 21; wherein the ferroelectric liquid crystal layer comprises a chiral smectic liquid crystal layer.
24. A liquid crystal display device as claimed in Claim 21; wherein the drive means includes means for applying an A.C. electric signal having a high frequency sufficient to maintain a desired display state.
25. A ferro-electric liquid crystal electro-optical device driven in a time-sharing mode comprising: a panel having a plurality of scanning electrodes, a plurality of display electrodes and a ferro-electric liquid crystal material disposed between the scanning electrodes and the display electrodes; drive means for scanning the scanning electrodes and for feeding display data signals to the display electrodes so as to produce a picture on the panel;
and control means for controlling said drive means to enable the same to scan only a part of the scanning electrodes for partially rewriting the picture produced by the panel.
and control means for controlling said drive means to enable the same to scan only a part of the scanning electrodes for partially rewriting the picture produced by the panel.
26. An electro-optical device as claimed in Claim 25;
wherein the ferro-electric liquid crystal material comprises a chiral smectic ferro-electric liquid crystal.
wherein the ferro-electric liquid crystal material comprises a chiral smectic ferro-electric liquid crystal.
27. An electro-optical device as claimed in Claim 25;
wherein the electro-optical device comprises a display device.
wherein the electro-optical device comprises a display device.
28. An electro-optical device as claimed in Claim 25;
wherein the electro-optical device comprises a shutter for a printer.
wherein the electro-optical device comprises a shutter for a printer.
29. An electro-optical device as claimed in Claim 25;
wherein the drive means applies an AC pulse voltage to the ferro-electric liquid crystal corresponding to the non-rewritten portion of the picture during the scanning so as to substantially maintain the display condition of the non-rewritten portion.
wherein the drive means applies an AC pulse voltage to the ferro-electric liquid crystal corresponding to the non-rewritten portion of the picture during the scanning so as to substantially maintain the display condition of the non-rewritten portion.
30. An electro-optical device as claimed in Claim 25;
wherein the drive means applies a voltage to the ferro-electric liquid crystal for changing the display condition of the picture corresponding to the rewritten portion of the picture and applies an AC pulse voltage to the ferro-electric liquid crystal for substantially maintaining the display condition of the picture corresponding to the rewritten portion of the picture during the scanning.
wherein the drive means applies a voltage to the ferro-electric liquid crystal for changing the display condition of the picture corresponding to the rewritten portion of the picture and applies an AC pulse voltage to the ferro-electric liquid crystal for substantially maintaining the display condition of the picture corresponding to the rewritten portion of the picture during the scanning.
31. An electro-optical device as claimed in Claim 25;
wherein the drive means imparts a high-impedance condition to both the rewritten and non-rewritten portions of the picture so that the conditions of the rewritten and non-rewritten portions of the picture are memorized after rewriting.
wherein the drive means imparts a high-impedance condition to both the rewritten and non-rewritten portions of the picture so that the conditions of the rewritten and non-rewritten portions of the picture are memorized after rewriting.
32. An electro-optical device as claimed in Claim 31;
wherein the drive means imparts the high-impedance condition to the entire picture after rewriting.
wherein the drive means imparts the high-impedance condition to the entire picture after rewriting.
33. An electro-optical device as claimed in Claim 26;
wherein the thickness of the chiral smectic ferro-electric liquid crystal material is thinner than the spiral pitch of the chiral smectic ferro-electric liquid crystal so that the liquid crystal loses the spiral structure and the molecules of the liquid crystal have bi-stable positions.
wherein the thickness of the chiral smectic ferro-electric liquid crystal material is thinner than the spiral pitch of the chiral smectic ferro-electric liquid crystal so that the liquid crystal loses the spiral structure and the molecules of the liquid crystal have bi-stable positions.
34. An electro-optical device as claimed in Claim 27;
wherein the drive means applies a voltage to the ferro-electric liquid crystal corresponding to the rewritten portion of the picture so that the liquid crystal molecules are moved from one of the bi-stable positions to the other, and applies an AC pulse voltage to the ferro-electric liquid crystal corresponding to the non-rewritten portion of the picture so that the liquid crystal molecules are not moved from one of the bi-stable positions to the other.
wherein the drive means applies a voltage to the ferro-electric liquid crystal corresponding to the rewritten portion of the picture so that the liquid crystal molecules are moved from one of the bi-stable positions to the other, and applies an AC pulse voltage to the ferro-electric liquid crystal corresponding to the non-rewritten portion of the picture so that the liquid crystal molecules are not moved from one of the bi-stable positions to the other.
35. An electro-optical device comprising: a panel for producing a picture, the panel comprising a ferro-electric liquid crystal layer, and scanning electrodes and display electrodes sandwiching therebetween the ferro-electric liquid crystal layer to define a plurality of picture elements at intersections of the scanning and display electrodes, the picture elements exhibiting one of two bi-stable optical conditions to collectively define the picture; a first drive circuit for scanning the scanning electrodes to successively select the picture elements aligned along respective scanning electrodes; a second drive circuit connected to the display electrodes and cooperative with the first drive circuit for applying a pulse to the selected picture elements to change the bi-stable optical condition thereof, and for applying AC
pulses to the non-selected picture elements to hold the bi-stable optical condition thereof; and control means connected to the first and second drive circuits and operative during a partial rewriting of the picture for designating a scanning range of the scanning electrodes corresponding to the rewritten portion of the picture so as to enable the first drive circuit to scan only the designated range of the scanning electrodes, and to enable the second drive circuit to apply the AC pulses to the picture elements located outside the designated scanning range.
pulses to the non-selected picture elements to hold the bi-stable optical condition thereof; and control means connected to the first and second drive circuits and operative during a partial rewriting of the picture for designating a scanning range of the scanning electrodes corresponding to the rewritten portion of the picture so as to enable the first drive circuit to scan only the designated range of the scanning electrodes, and to enable the second drive circuit to apply the AC pulses to the picture elements located outside the designated scanning range.
36. An electro-optical device as claimed in Claim 35;
wherein the second drive circuit includes means for applying a pulse of a given polarity to switch the selected picture elements from the dark to the bright condition, and for applying a pulse of an opposite polarity to switch the selected picture elements from the bright to the dark condition.
wherein the second drive circuit includes means for applying a pulse of a given polarity to switch the selected picture elements from the dark to the bright condition, and for applying a pulse of an opposite polarity to switch the selected picture elements from the bright to the dark condition.
37. An electro-optical device as claimed in Claim 36;
wherein the second drive circuit includes means for applying a pulse of a given polarity to switch the selected picture elements from the dark to the bright condition, and for applying a pulse of an opposite polarity to switch the selected picture elements from the bright to the dark condition.
wherein the second drive circuit includes means for applying a pulse of a given polarity to switch the selected picture elements from the dark to the bright condition, and for applying a pulse of an opposite polarity to switch the selected picture elements from the bright to the dark condition.
38. An electro-optical device as claimed in Claim 35;
wherein the ferro-electric liquid crystal layer comprises a chiral smectic ferro-electric liquid crystal.
wherein the ferro-electric liquid crystal layer comprises a chiral smectic ferro-electric liquid crystal.
39. An electro-optical device as claimed in Claim 35;
wherein the control means includes means for enabling the first and second drive circuits to connect a high-impedance to the picture elements after the scanning operation.
wherein the control means includes means for enabling the first and second drive circuits to connect a high-impedance to the picture elements after the scanning operation.
40. An electro-optical device as claimed in Claim 35;
wherein the panel includes means for establishing the two bi-stable optical conditions of the picture elements based on bi-stable alignment of the molecules of the ferro-electric liquid crystal layer.
wherein the panel includes means for establishing the two bi-stable optical conditions of the picture elements based on bi-stable alignment of the molecules of the ferro-electric liquid crystal layer.
41. An electro-optical device as claimed in Claim 35;
wherein the electro-optical device comprises a display device.
wherein the electro-optical device comprises a display device.
42. An electro-optical device as claimed in Claim 35;
wherein the electro-optical device comprises a shutter for a printer.
wherein the electro-optical device comprises a shutter for a printer.
43. An electro-optical device as claimed in Claim 35;
wherein the control means defines a rewriting area to define the part of the scanning electrodes to be scanned by the drive means.
wherein the control means defines a rewriting area to define the part of the scanning electrodes to be scanned by the drive means.
44. An electro-optical device as claimed in Claim 35;
wherein the control means defines a rewriting area to define the part of the scanning electrodes to be scanned by the drive means.
wherein the control means defines a rewriting area to define the part of the scanning electrodes to be scanned by the drive means.
45. A driving method for an optical modulation device having a plurality of picture elements arranged in a matrix and comprising scanning lines, data lines spaced apart from and intersecting with the scanning lines, and a chiral smectic liquid crystal, assuming a first orientation state or a second orientation state depending on the direction of an electric field applied thereto, interposed between the scanning lines and the data lines, each of the intersections between the scanning lines and the data lines forming one of said plurality of picture elements; said driving method comprising :
applying a scanning selection signal to the scanning lines sequentially, said scanning selection signal comprising a voltage phase of one polarity and a voltage phase of the other polarity respectively with respect to a voltage applied to a non-selected scanning line; and applying an information signal in phase with the scanning selection signal; said information signal comprising a voltage signal providing a voltage exceeding the first threshold voltage of the chiral smectic liquid crystal applied to the picture elements on a selected scanning line in phase with said voltage phase of one polarity, a voltage signal providing a voltage exceeding the second threshold voltage of the chiral smectic liquid crystal applied to a selected picture element on the selected scanning line in phase with said voltage phase of the other polarity, and an auxiliary signal;
said auxiliary signal providing an inversion preventing voltage, in combination with the voltage applied to the non-selected scanning line before the application period of a voltage of one and the same polarity becomes so extended that the first or second orientation state of a picture element on the non-selected scanning line formed when the picture element was placed on a selected scanning line, becomes inverted due to maintenance of said voltage of one and the same polarity, the inversion preventing voltage having either a voltage of 0 or a polarity opposite to that of said voltage of one and the same polarity.
applying a scanning selection signal to the scanning lines sequentially, said scanning selection signal comprising a voltage phase of one polarity and a voltage phase of the other polarity respectively with respect to a voltage applied to a non-selected scanning line; and applying an information signal in phase with the scanning selection signal; said information signal comprising a voltage signal providing a voltage exceeding the first threshold voltage of the chiral smectic liquid crystal applied to the picture elements on a selected scanning line in phase with said voltage phase of one polarity, a voltage signal providing a voltage exceeding the second threshold voltage of the chiral smectic liquid crystal applied to a selected picture element on the selected scanning line in phase with said voltage phase of the other polarity, and an auxiliary signal;
said auxiliary signal providing an inversion preventing voltage, in combination with the voltage applied to the non-selected scanning line before the application period of a voltage of one and the same polarity becomes so extended that the first or second orientation state of a picture element on the non-selected scanning line formed when the picture element was placed on a selected scanning line, becomes inverted due to maintenance of said voltage of one and the same polarity, the inversion preventing voltage having either a voltage of 0 or a polarity opposite to that of said voltage of one and the same polarity.
46. The driving method according to Claim 45, wherein one period for applying a voltage to the picture elements on the selected scanning line comprises : a first phase for applying to all or a prescribed number of the picture elements on the selected scanning line a voltage exceeding the first threshold voltage for causing the first orientation state of the ferroelectric liquid crystal; a second phase for applying to a selected picture element among said all or a prescribed number of the picture elements a voltage exceeding the second threshold voltage for causing the second orientation state of the chiral smectic liquid crystal; and a third phase for applying an auxiliary signal to data lines thereby to apply a voltage between the first and second threshold voltages to said all or prescribed number of the picture elements.
47. The driving method according to Claim 46, wherein said auxiliary signal applied to data lines in the third phase has a voltage polarity opposite to that of the voltage applied to the data lines in the second phase, with respect to the voltage applied to the non-selected scanning lines.
48. The driving method according to Claim 46, wherein said third phase has a period of t3 and said second phase has a period of t2, said t3 and t2 satisfying the relationship t3 > t2.
49. The driving method according to Claim 46, wherein, in the second phase, an information selection signal is applied to a selected data line and an information non-selected signal is applied to a non-selected data line, said information selection signal and information non-selected signal having different voltage polarities with respect to the voltage applied to the non-selected scanning lines.
50. The driving method according to Claim 46, wherein after said one period of voltage application comprising the first to third phases is effected for the selected scanning line, another one period of voltage application comprising the first to third phases of voltage application is effected for a subsequently selected scanning line.
51. The driving method according to claim 45, wherein said chiral smectic liquid crystal is in a non-spiral structure.
52. The driving method according to claim 45, which comprises applying an alternating voltage below the threshold voltages to the picture elements on the non-selected scanning line.
53. An optical modulation device having a plurality of picture elements arranged in a matrix and comprising scanning lines, data lines spaced apart from and intersecting with the scanning lines, and a chiral smectic liquid crystal, assuming a first orientation state or a second orientation state depending on the direction of an electric field applied thereto, interposed between the scanning lines and the data lines, each of the intersections between the scanning lines and the data lines forming one of said plurality of picture elements; said optical modulation device comprising means for:
applying a scanning selection signal to the scanning lines sequentially, said scanning selection signal comprising a voltage phase of one polarity and a voltage phase of the other polarity respectively with respect to a voltage applied to a non-selected scanning line; and applying an information signal in phase with the scanning selection signal; said information signal comprising a voltage signal providing a voltage exceeding the first threshold voltage of the chiral smectic liquid crystal applied to the picture elements on a selected scanning line in phase with said voltage phase of one polarity, voltage signal providing a voltage exceeding the second threshold voltage of the chiral smectic liquid crystal applied to a selected picture element on the selected scanning line in phase with said voltage phase of the other polarity, and an auxiliary signal;
said auxiliary signal providing an inversion preventing voltage in combination with the voltage applied to the non-selected scanning lines before the application period of a voltage of one and the same polarity becomes so great that the first or second orientation state of a picture element on the non-selected scanning line, formed when the picture element is placed on a selected scanning line, is inverted due to said voltage of one and the same polarity, the inversion preventing voltage being a voltage of O or a polarity opposite to that of said voltage of one and the same polarity.
applying a scanning selection signal to the scanning lines sequentially, said scanning selection signal comprising a voltage phase of one polarity and a voltage phase of the other polarity respectively with respect to a voltage applied to a non-selected scanning line; and applying an information signal in phase with the scanning selection signal; said information signal comprising a voltage signal providing a voltage exceeding the first threshold voltage of the chiral smectic liquid crystal applied to the picture elements on a selected scanning line in phase with said voltage phase of one polarity, voltage signal providing a voltage exceeding the second threshold voltage of the chiral smectic liquid crystal applied to a selected picture element on the selected scanning line in phase with said voltage phase of the other polarity, and an auxiliary signal;
said auxiliary signal providing an inversion preventing voltage in combination with the voltage applied to the non-selected scanning lines before the application period of a voltage of one and the same polarity becomes so great that the first or second orientation state of a picture element on the non-selected scanning line, formed when the picture element is placed on a selected scanning line, is inverted due to said voltage of one and the same polarity, the inversion preventing voltage being a voltage of O or a polarity opposite to that of said voltage of one and the same polarity.
54. The optical modulation device according to Claim 53, which comprises means for applying an alternating voltage below the threshold voltages to the picture elements on the non-selected scanning line.
55. An optical modulation device, comprising: a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second stable states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels: and signal application means including means for defining a rewriting region and a non-rewriting region in the matrix of picture elements, means for applying a first writing voltage exceeding the first threshold level or a second writing voltage exceeding the second threshold level to selected picture elements in the rewriting region depending on the given information, while applying a scanning signal sequentially to the scanning electrodes corresponding to the rewriting region;
and means for applying a voltage between the first and second threshold levels to the picture elements in the non-rewriting region.
and means for applying a voltage between the first and second threshold levels to the picture elements in the non-rewriting region.
56. An optical modulation device comprising:
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels: and signal application means including means for defining a rewriting region and a non-rewriting region in the matrix of picture elements, means for sequentially applying a scanning signal to the scanning electrodes corresponding to the rewriting region and applying an information signal to the signal electrodes in phase with the scanning signal so as to select either one of the first and second orientation states of the liquid crystal at the respective picture elements on the scanning electrodes in the rewriting region depending on given information data and for, prior to the sequential application of the scanning signal, applying a clearing voltage signal to the scanning electrodes so as to clear all or a prescribed number of the picture elements on the scanning electrodes in the rewriting region into the first orientation state; and means for applying a voltage between the first and second threshold levels to the picture elements in the non-rewriting region.
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels: and signal application means including means for defining a rewriting region and a non-rewriting region in the matrix of picture elements, means for sequentially applying a scanning signal to the scanning electrodes corresponding to the rewriting region and applying an information signal to the signal electrodes in phase with the scanning signal so as to select either one of the first and second orientation states of the liquid crystal at the respective picture elements on the scanning electrodes in the rewriting region depending on given information data and for, prior to the sequential application of the scanning signal, applying a clearing voltage signal to the scanning electrodes so as to clear all or a prescribed number of the picture elements on the scanning electrodes in the rewriting region into the first orientation state; and means for applying a voltage between the first and second threshold levels to the picture elements in the non-rewriting region.
57. A device according to claim 56, wherein said clearing voltage signal is applied at a time to the scanning electrodes corresponding to the rewriting region.
58. A device according to claim 56, wherein said clearing voltage signal is sequentially applied to the scanning electrodes corresponding to the rewriting region.
55. An optical modulation device comprising:
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels: and signal application means including means for defining a rewriting region and a non-rewriting region in the matrix of picture elements, means for sequentially applying a scanning signal to the scanning electrodes corresponding to the rewriting region and applying an information signal to the signal electrodes in phase with the scanning signal so as to select either one of the first and second orientation states of the liquid crystal at the respective picture elements on the scanning electrodes in the rewriting region depending on given information data and for, prior to the sequential application of the scanning signal, applying a clearing voltage signal to the scanning electrodes so as to clear all or a prescribed number of the picture elements on the scanning electrodes in the rewriting region into the first orientation state:
means for applying an AC voltage to the picture elements on a scanning electrode which is not supplied with the scanning signal electrode which is not supplied with the scanning signal in the rewriting region, said AC voltage not changing the first or second orientation state of the liquid crystal selected at the respective picture elements when the scanning electrodes is supplied with the scanning signal: and means for applying a voltage between the first and second threshold levels to the picture elements in the non-rewriting region.
55. An optical modulation device comprising:
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels: and signal application means including means for defining a rewriting region and a non-rewriting region in the matrix of picture elements, means for sequentially applying a scanning signal to the scanning electrodes corresponding to the rewriting region and applying an information signal to the signal electrodes in phase with the scanning signal so as to select either one of the first and second orientation states of the liquid crystal at the respective picture elements on the scanning electrodes in the rewriting region depending on given information data and for, prior to the sequential application of the scanning signal, applying a clearing voltage signal to the scanning electrodes so as to clear all or a prescribed number of the picture elements on the scanning electrodes in the rewriting region into the first orientation state:
means for applying an AC voltage to the picture elements on a scanning electrode which is not supplied with the scanning signal electrode which is not supplied with the scanning signal in the rewriting region, said AC voltage not changing the first or second orientation state of the liquid crystal selected at the respective picture elements when the scanning electrodes is supplied with the scanning signal: and means for applying a voltage between the first and second threshold levels to the picture elements in the non-rewriting region.
59
60. A device according to claim 59, wherein said clearing voltage signal is applied at a time to the scanning electrodes corresponding to the rewriting region.
61. A device according to claim 59, wherein said clearing voltage signal is sequentially applied to the scanning electrodes corresponding to the rewriting region.
62. An optical modulation device comprising:
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels; and signal application means including means for defining a rewriting region and a non-rewriting region in the matrix of picture elements, means for sequentially applying a scanning signal to the scanning electrodes corresponding to the rewriting region and applying an information signal to the signal electrodes in phase with the scanning signal so as to select either one of the first and second orientation states of the liquid crystal at the respective picture elements on the scanning electrodes in the rewriting region depending on given information data and for, prior to the sequential application of the scanning signal, applying a clearing voltage signal to the scanning electrodes so as to clear all or a prescribed number of the picture elements on the scanning electrodes in the rewriting region into the first orientation state; and means for applying an AC voltage to the picture elements on the scanning electrodes in the non-writing region, said AC voltage not changing the first or second orientation state of the liquid crystal selected at the respective picture elements.
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and spaced apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels; and signal application means including means for defining a rewriting region and a non-rewriting region in the matrix of picture elements, means for sequentially applying a scanning signal to the scanning electrodes corresponding to the rewriting region and applying an information signal to the signal electrodes in phase with the scanning signal so as to select either one of the first and second orientation states of the liquid crystal at the respective picture elements on the scanning electrodes in the rewriting region depending on given information data and for, prior to the sequential application of the scanning signal, applying a clearing voltage signal to the scanning electrodes so as to clear all or a prescribed number of the picture elements on the scanning electrodes in the rewriting region into the first orientation state; and means for applying an AC voltage to the picture elements on the scanning electrodes in the non-writing region, said AC voltage not changing the first or second orientation state of the liquid crystal selected at the respective picture elements.
63. A device according to claim 62, wherein said clearing voltage signal is applied at a time to the scanning electrodes corresponding to the rewriting region.
64. A device according to claim 62, wherein said clearing voltage signal is sequentially applied to the scanning electrodes corresponding to the rewriting region.
65. An optical modulation device comprising :
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and space apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels, and signal application means including means for designating the start and finish of scanning to define a rewriting region and a non-rewriting region in the matrix of picture elements, means for applying a first writing voltage exceeding the first threshold level or a second writing voltage exceeding the second threshold level to selected picture elements in the rewriting region depending on the given information, while applying a scanning signal sequentially to the scanning electrodes corresponding to the rewriting region; and means for applying a voltage between the first and second threshold levels to the picture elements in the non-writing region.
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and space apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels, and signal application means including means for designating the start and finish of scanning to define a rewriting region and a non-rewriting region in the matrix of picture elements, means for applying a first writing voltage exceeding the first threshold level or a second writing voltage exceeding the second threshold level to selected picture elements in the rewriting region depending on the given information, while applying a scanning signal sequentially to the scanning electrodes corresponding to the rewriting region; and means for applying a voltage between the first and second threshold levels to the picture elements in the non-writing region.
66. An optical modulation device comprising :
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and space apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels: and signal application means including means for defining a rewriting region and a non-rewriting region in the matrix of picture elements, means for applying a first writing voltage exceeding the first threshold level or a second writing voltage exceeding the second threshold level to selected picture elements in the rewriting region depending on the given information, while applying a scanning signal sequentially to the scanning electrodes corresponding to the rewriting region;
means for applying an AC voltage to the picture elements on a scanning electrode which is not supplied with the scanning signal in the rewriting region, said AC voltage not changing the first or second orientation state of the liquid crystal selected at the respective picture elements when the scanning electrodes is supplied with the scanning signal; and means for applying a voltage between the first and second threshold levels to the picture elements in the non-rewriting region.
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and space apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels: and signal application means including means for defining a rewriting region and a non-rewriting region in the matrix of picture elements, means for applying a first writing voltage exceeding the first threshold level or a second writing voltage exceeding the second threshold level to selected picture elements in the rewriting region depending on the given information, while applying a scanning signal sequentially to the scanning electrodes corresponding to the rewriting region;
means for applying an AC voltage to the picture elements on a scanning electrode which is not supplied with the scanning signal in the rewriting region, said AC voltage not changing the first or second orientation state of the liquid crystal selected at the respective picture elements when the scanning electrodes is supplied with the scanning signal; and means for applying a voltage between the first and second threshold levels to the picture elements in the non-rewriting region.
67. An optical modulation device comprising :
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and space apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels; and signal application means including means for defining a rewriting region and a non-rewriting region in the matrix of picture elements, means for applying a first writing voltage exceeding the first threshold level or a second writing voltage exceeding the second threshold level to selected picture elements in the rewriting region depending on the given information, while applying a scanning signal sequentially to the scanning electrodes corresponding to the rewriting region; and means for applying an AC voltage to the picture elements on the scanning electrodes in the non-rewriting region, said AC voltage not changing the first or second orientation state of the liquid crystal selected at the respective picture elements.
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and space apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels; and signal application means including means for defining a rewriting region and a non-rewriting region in the matrix of picture elements, means for applying a first writing voltage exceeding the first threshold level or a second writing voltage exceeding the second threshold level to selected picture elements in the rewriting region depending on the given information, while applying a scanning signal sequentially to the scanning electrodes corresponding to the rewriting region; and means for applying an AC voltage to the picture elements on the scanning electrodes in the non-rewriting region, said AC voltage not changing the first or second orientation state of the liquid crystal selected at the respective picture elements.
68. An optical modulation device comprising :
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and space apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels; and signal application means including means for sequentially applying a scanning signal to the scanning electrodes corresponding to the rewriting region and applying an information signal to the signal electrodes in phase with the scanning signal so as to select either one of the first and second orientation states of the liquid crystal at the respective picture elements on the scanning electrodes in the rewriting region depending on given information data and for, prior to the sequential application of the scanning signal, applying a clearing voltage signal to the scanning electrodes so as to clear all or a prescribed number of the picture elements on the scanning electrodes in the rewriting region into the first orientation state.
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and space apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels; and signal application means including means for sequentially applying a scanning signal to the scanning electrodes corresponding to the rewriting region and applying an information signal to the signal electrodes in phase with the scanning signal so as to select either one of the first and second orientation states of the liquid crystal at the respective picture elements on the scanning electrodes in the rewriting region depending on given information data and for, prior to the sequential application of the scanning signal, applying a clearing voltage signal to the scanning electrodes so as to clear all or a prescribed number of the picture elements on the scanning electrodes in the rewriting region into the first orientation state.
69. A device according to claim 68, wherein said clearing voltage signal is applied at a time to the scanning electrodes corresponding to the rewriting region.
70. A device according to claim 68, wherein said clearing voltage signal is sequentially applied to the scanning electrodes corresponding to the rewriting region.
71. An optical modulation device comprising :
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and space apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels; and signal application means including means for defining a rewriting region and a non-rewriting region in the matrix of picture elements, means for sequentially applying a scanning signal to the scanning electrodes so as to select a scanning electrode and applying an information signal to the signal electrodes in phase with the scanning signal so as to select either one of the first and second orientation states of the liquid crystal at the respective picture elements on the scanning electrodes in the rewriting region depending on given information data and for, prior to the sequential application of the scanning signal, applying a clearing voltage signal to the scanning electrodes so as to clear all or a prescribed number of the picture elements on the scanning electrodes in the rewriting region into the first orientation state; and means for applying an AC voltage to the picture elements on a scanning electrode which is not selected, said AC voltage not changing the first or second orientation state of the liquid crystal selected at the respective picture elements when the scanning electrodes is selected.
a ferroelectric liquid crystal device having a group of scanning electrodes arranged in a matrix with and space apart from a group of signal electrodes with a ferroelectric liquid crystal disposed therebetween to form picture elements at intersections of the scanning and signal electrodes, the liquid crystal being orientable to first and second orientation states upon application of electric fields of respective opposite directions greater than respective first and second threshold levels; and signal application means including means for defining a rewriting region and a non-rewriting region in the matrix of picture elements, means for sequentially applying a scanning signal to the scanning electrodes so as to select a scanning electrode and applying an information signal to the signal electrodes in phase with the scanning signal so as to select either one of the first and second orientation states of the liquid crystal at the respective picture elements on the scanning electrodes in the rewriting region depending on given information data and for, prior to the sequential application of the scanning signal, applying a clearing voltage signal to the scanning electrodes so as to clear all or a prescribed number of the picture elements on the scanning electrodes in the rewriting region into the first orientation state; and means for applying an AC voltage to the picture elements on a scanning electrode which is not selected, said AC voltage not changing the first or second orientation state of the liquid crystal selected at the respective picture elements when the scanning electrodes is selected.
72. A device according to claim 71, wherein said clearing voltage signal is applied at a time to the scanning electrodes corresponding to the rewriting region.
73. A device according to claim 71, wherein said clearing voltage signal is sequentially applied to the scanning electrodes corresponding to the rewriting region.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000472482A CA1258327A (en) | 1985-01-21 | 1985-01-21 | Driving method for optical modulation device |
| CA000582351A CA1278890C (en) | 1984-01-23 | 1988-11-04 | Driving method for optical modulation device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000472482A CA1258327A (en) | 1985-01-21 | 1985-01-21 | Driving method for optical modulation device |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000582351A Division CA1278890C (en) | 1984-01-23 | 1988-11-04 | Driving method for optical modulation device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1258327A true CA1258327A (en) | 1989-08-08 |
Family
ID=4129625
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000472482A Expired CA1258327A (en) | 1984-01-23 | 1985-01-21 | Driving method for optical modulation device |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1258327A (en) |
-
1985
- 1985-01-21 CA CA000472482A patent/CA1258327A/en not_active Expired
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