GB2160002A

GB2160002A - Electrochromic display devices

Info

Publication number: GB2160002A
Application number: GB08510619A
Authority: GB
Inventors: Seigo Togashi
Original assignee: Citizen Watch Co Ltd
Current assignee: Citizen Watch Co Ltd
Priority date: 1984-04-27
Filing date: 1985-04-26
Publication date: 1985-12-11
Also published as: GB8510619D0

Abstract

An active matrix type electrochromic display device having a plurality of picture elements addressed through the scanning and data lines, wherein each of the picture elements has an electrochromic display element and unidirectional elements, for example, diodes for controlling a positive or negative charge to be injected into the electrochromic display element. The unit picture element may alternatively comprises a series circuit of electrochromic display element and a non-linear elements having a threshold voltage. Line-sequential scanning signals are supplied to the scanning lines, and data signals based on display contents are supplied to the data lines so as to inject charges in the electro-chromic display elements and to update the display states thereof. The method of driving is performed based on predetermined applied voltage, non-selection potential and selection potential. The EC element may be connected via separate diodes to different driver lines. <IMAGE>

Description

SPECIFICATION Electrochromic display device and method for driving the same Background of the Invention 1. Field of the Invention The present invention relates to an electrochromic display device and a method for driving the same.

More particularly, it relates to a so-called "active matrix" type electrochromic display device wherein switching elements are respectively arranged in picture elements and are driven by multiplexing.

The present invention is advantageously used for a display board, a display panel, a wristwatch, and the like.

2. Description of the Related Art An electrochromic (hereinafter referred to as EC) display device is one of the most promising of the recent two-dimensional (plane) display devices which can be driven by a low power and at a low voltage to provide a high quality display equal to that of a liquid crystal display device. However, a conventional EC device cannot be easily multiplexed to obtain a high-density display. To overcome this drawback, an "active matrix" method is known wherein switching elements are respectively arranged in picture elements and multiplexed at a high rate of divisional efficiency. For example, an active matrix EC display device using MOS transistors as switching elements is disclosed in U.S.P.No. 4,228,431, and an EC display using metal-insulator-metal (MIM) elements is disclosed in Japanese Patent Publication No 58-52679 However, these EC elements have many disadvantages and are not practical, as described in more detail later.

Summary of the Invention The primary object of the present invention is to provide an electrochromic display device having a novel structure.

Another object of the present invention is to provide a method for driving such a novel electrochromic display device.

In accordance with the present invention, there is provided an electrochromic display device comprising: a plurality of scanning lines, a plurality of data lines, and a plurality of unit picture elements which are addressed through the scanning line and the data line, each unit picture element having an electrochromic display element and unidirectional elements for controlling a charge injected therein.

Brief Description of the Drawings In the drawings; Figure 1 is a circuit diagram showing the picture element arrangement of a conventional TFT type EC display device; Figure 2 is a circuit diagram showing the picture element arrangement of a conventional MIM type EC display device; Figure 3 shows the I-V characteristics of the MIM element; Figures 4 and 9 are block diagrams of EC display devices according to two embodiments of the present invention; Figures 5 and 10 show the picture element arrangements of the devices shown in Figs 4 and 9, respectively; Figures 6 and 11 show waveform charts of the devices shown in Figs 5 and 10, respectively; Figures 7A and 7B are a plan view and a sectional view, respectively, of a unit picture element; Figure 8 is a graph showing the l-V characteristics of an amorphous silicon diode;; Figure 12 is a block diagram of still another embodiment of the present invention; Figure 13 shows the picture element arrangement of the device shown in Fig. 12; Figure 14 is a graph showing the I-V characteristics of an amorphous silicon diode ring; Figures 15A and 15B are a plan view and a sectional view of a unit picture element, respectively; and Figures 16 and 17 show waveform charts of the device shown in Fig. 12.

Description of the Preferred Embodiments Before describing the preferred embodiments, an explanation will be given of a conventional electrochromic display device.

Figure 1 shows an example of picture element arrangements of an active matrix EC display device of the transistor address type as disclosed in U.S.P No. 4,228,431. Referring to Fig 1, data lines D1 and D2 are connected to sources 2 of transistors TR, scanning lines S1 and S2 are connected to gates 1 thereof, and EC elements EC are connected to drains 3 thereof. In response to scanning signals supplied to the scanning lines, the gates of the corresponding transistors are enabled or disabled, and positive or negative charges are injected from the data lines into display electrodes 4 of the elements EC, thereby turning the display on or off.

Figure 2 shows an example of the picture element arrangement of an active matrix EC display device of the MIM element address type as disclosed in Japanese Patent Publication No 58-52679. An MIM element MIM has the current vs. voltage characteristics as shown in the graph of Fig. 3 and serves as a switching element upon a change from state a to state b. Each EC element EC is connected in series with the corresponding MIM element MIM between data lines D1 and D2 and scanning lines S1 and S2, and serves to inject or hold a positive or negative charge in accordance with the switching operation of the MIM element, thereby turning the display on or off.

The display device of the transistor address type as shown in Fig. 1 has the following disadvantages.

When each transistor is a MOS transistor using a bulk silicon substrate, an element having a large area is hard to manufacture due to limitations in the manufacture of silicon wafers, and the material cost is also very high. Due to these disadvantages, no advance in techniques relating to display devices of the MOS transistor address type has been reported.

The use of a thin film transistor (TFT) using amorphous silicon (a-Si) or the like in place of a MOS transistor is also known in association with a liquid crystal display device of the TFT address type. However, taking into consideration of the size of a TFT element, normally an ON current of only 1 to 5 FA can be obtained. When the coloring/bleach charge of the EC element is assumed to be about 5 mC/cm2. 1 to 5 seconds are required to turn on or off a square picture element having a size of 300 Am per side. When scanning is performed by the line sequential method, this time of 1 to 5 seconds corresponds to the rewrite time of one dot line. Therefore, it takes 7 to 35 seconds to display one line of alphanumeric characters in a 7 x 5 dot matrix, with the result that such a display device is impractical.The ON current of a TFT depends on electron mobility as one property of a semiconductor. Therefore, unless the electron mobility is improved 10 to 100 times, a display device of the TFT address type cannot be used in practice.

The MIM element shown in Fig 2 also has a similar problem. In Japanese Patent Publication No 5852679, the ON current of an MIM element is reported to be 50 mA/cm2. Therefore, even if MIM elements can be formed for all the picture elements, 1 second is required to update 10 dot lines or 1.4 character lines, also resulting in an impractical device. The MIM element has a further problem of a high OFF current. As can be seen from Fig. 3, the ON-OFF ratio of the MIM element is only 2 to 3. This means that only 2 to 3 dot lines can be displayed, and thus a high-density display cannot be achieved with the technique as disclosed in Japanese Patent Publication No. 58-52679.

As described above, the conventional display devices have problems concerning ON current, OFF current, area, and cost, and are therefore impractical.

According to the present invention, a novel arrangement of an active matrix is used to provide an EC display device which is substantially free from the problems of the conventional devices The present invention will be described in detail with reference to the accompanying drawings.

Figure 4 is a block diagram of an electrochromic display device according to an embodiment of the present invention. A display panel 41 has data lines D(1), D(2) ..., D(l) ..., D(M); two groups of scanning lines, one group consisting of a plurality of scanning lines SA(1), SA(2), SA(J) ..., SA(N), and the other group consisting of a plurality of scanning lines SB(1), Sub(2) ..., SB(J), ... SB(N); and a plurality of unit picture elements as shown in Fig. 5. A unit picture element has a single electrochromic display element EC(I, J) and two unidirectional elements, i.e., diodes RA(l,J) and RB(I, J).One end of the electrochromic display element EC(I,J) is connected to the data line D(l). A display electrode DE(I,J) at the other end of the element EC(I,J) is connected to the forward direction terminal (anode) of the first diode RA(I,J) and to the reverse direction terminal (cathode) of the second diode RB(I,J). The reverse direction terminal of the first diode RA(I,J) is connected to the first scanning line SA(J), and the forward direction terminal of the second diode RB(I,J) is connected to the scanning lines SB(I) A data line driver 42 supplies a data signal to the data lines; scanning line drivers 43 and 44 supply scanning signals to the scanning lines; video processor 45 supplies a serial video signal to the data line driver; and clock generator 46 supplies various timing pulses to the respective drivers.

One characteristic feature of the present invention lies in the picture element arrangement. More specifically, a single EC display element is connected to two diodes, which are separately connected to corresponding lines. Thus, a positive charge is injected through one diode, while a negative charge is injected through the other diode.

Figure 6 shows examples of drive waveform charts according to the present invention. Referring to Fig.

6, reference symbol TW corresponds to a write phase, and reference symbol TE corresponds to an erase phase. The phase TW and TE respectively correspond to time intervals in which positive and negative charges are injected into the display electrode DE(I,J) of the EC element shown in Fig. 5. Reference symbol (I) is an example of a data signal supplied to the data electrode. In the write phase TW, the signal W(I) is at a write potential -v in the write mode, and is at a hold potential +v in the non-write mode. The polarity of the signal it,(l) is inverted in the erase phase TE, i e., the erase potential is +v and the hold potential is -v.In the write phase TW, a scanning signal A(J) supplied to the scanning line SA(J) connected to the negative charge injection diode RA(I,J) is kept at a positive hold potential (in this case, +2 V) so that the diode RA(I,J) will not be forward biased and allow a current flow thereto irrespective of a data signal +(I) of the value within a range of +v and -v. In the erase phase TE, the signal A(J) is kept at the erase potential 0 for the time "te" corresponding to the scanning line to be erased and at the hold potential +2v in during the remaining time as in the write phase.A scanning signal B(J) supplied to the scanning line SB(J) connected to the positive charge injection diode RB(I,J) is at the potential having the opposite polarity to that of the scanning signal A(J). The signal B(J) is at the write potential 0 for the time "tw" corresponding to the scanning line to be written and is at the hold potential -2v during the remaining time.

When signals having the potentials as described above are used, a positive voltage is applied and a positive charge is injected into the EC element, as indicated by a hatched portion 61 in Fig. 6, only when the scanning signal B(J) is at the write potential 0 and the data signal W(I) is at the write potential -v.

For erasing, only when the scanning signal A(J) is at the erase potential 0 and the data signal +(I) is at the erase potential +v, a negative voltage is applied and a negative charge is injected as indicated by a hatched portion 62.

At times other than the write and erase modes as described above, charge injection is not performed and the display is held even if one of the scanning and data signals is set at the write or erase potential.

Note that the voltage v is an EC element drive voltage having a value of about 1.0 to 1.5 V. Therefore, the peak to peak voltage 4v is 4 to 6 V, and thus the device can be driven by a very low drive voltage. When the forward characteristics of the diode have an offset voltage Vth, the write potential 0 of the scanning signal in the write phase must be set at +Vth and the erase potential 0 in the erase phase must be set at with. In the a-Si diode used in the above embodiment, the offset voltage V,h is about 0.7 to 0.9 V.

Figure 7A and 7B are, respectively, a plan view of a unit picture element shown in Fig. 5 and a sectional view along the line A - A' thereof A metal layer for scanning electrodes SA(J) and SB(J) such as a Cr or Mo layer is formed on a substrate 75 of glass or the like. Semiconductor layers such as a-Si P.l.N layers as the diodes RA(I,J) and RB(I,J) are formed thereover. After forming an insulating interlayer 74, e.g., an SiO2 or SiN layer, a transparent electrode as a display electrode for the display electrode DE(I,J), an lr(OH) layer 73 for forming EC elements, a Tea205 layer 76, and a WO3 layer 77, a transparent electrode as a data line D(l) is formed.If required, a passivation layer or a sealing structure is adopted to protect the underlying structure. Reference numerals 71 and 72 denote contacts.

Figure 9 is a block diagram of another embodiment of the present invention, and Fig. 10 shows a unit picture element thereof. This embodiment is different from the former embodiment in that data lines are divided into two groups A and B. In this embodiment, a unit picture element has a single electrochromic display element EC(I,J) and two diodes RA(I,J) and RB(I,J). One end of the electrochromic display element EC(I,J) is connected to a scanning line S(J), and a display electrode DE(I,J) at the other end of the element EC(I,J) is connected to the forward direction terminal of the first diode RA(I,J) and the reverse direction terminal of the second diode RB(I,J). The reverse direction terminal of the first diode RA(I,J) is connected to a first data line DA(I), and the forward direction terminal of the second diode RB(I,J) is connected to a second data line DB(I). In this embodiment, two data line drivers 92 and 93 and a single scanning line driver 91 are provided.

Figure 11 shows an example of drive waveforms of the embodiment shown in Figs. 10 and 11. The scanning signal (J) is a two-potential signal of +V; in the write phase TW, it is at the write potential -v in the write interval "tw" and is at the hold potential +v during the remaining time. In the erase phase TE, the signal (J) is at the erase potential +v in the erase interval "te" and is at the hold potential -v during the remaining time. Data signal A(I) takes to states of erase potential 0 and hold potential +2V, and data signal WB(I) takes two states of write potential 0 and hold potential -2v.

In the embodiment shown in Figs 9, 10 and 11, the respective signals are bistable signals and the arrangement of the drivers can be simple as in the embodiment shown in Figs. 4, 5, and 6.

Figure 12 is a block diagram of an electrochromic display device according to still another embodiment of the present invention. A display panel 41 has data lines D(1), D(2) ..., D(l), ... D(M), and scanning lines 5(1), S(2) ..., S(J) ..., D(M). Unit picture elements shown in Fig. 13 are formed at the respective intersections of the data and scanning lines. Referring to Fig. 13, a display electrode DE(I,J) at one terminal of an electrochromic display element EC(I,J) is connected in series with a non-linear element constituted by a diode ring DR(I,J). In the diode ring DR(I,J), a series circuit of diode groups 131 and 132 and a series of diode groups 133 and 134 are connected in parallel with each other in such a manner that the forward direction terminals of the diode groups 131 and 132 are connected to the side of the display electrode DE(I,J), while those of the diode groups 133 and 134 are connected to the side of the scanning lines S(J).Each of the diode groups serves to inject negative and positive charges into the display electrode DE(I,J), and their current vs. voltage characteristics are non-linear having threshold voltages of +Vth as shown in Fig 14. The threshold voltage V,h depends on the type and number of diodes of the diode ring DR(I,J). A data line driver 121 supplies a data signal according to the display contents to the data lines, and a scanning line driver 122 supplies line-sequential scanning signals to the scanning line.

Figures 15A and 15B are respectively a plan view of a unit picture element shown in Fig. 13 and a sectional view along the line A - A' thereof. A first electrode layer of Cr, Mo, or Ni serving as the scanning lines S(J) and connection electrodes is formed on a substrate 154 of glass or the like. Thereafter, diode layers 131, 132, 133 and 134 are formed. The diode layers are a-Si layers formed by a so-called plasma-CVD method. In this embodiment, in order to obtain a high threshold voltage, two sets of P.l.N layers are formed through a thin metal layer interposed therebetween. An insulating interlayer 155 is formed on the structure. After contact holes are formed on contacts 151, 152, and 153 and the non-linear element, second electrode layers 162 and 156 are formed. Thus, the diode ring DR(I,J) as shown in Fig.

13 is formed. EC layers 157, 158, and 159 are then formed. In this embodiment, the first EC layer 157 is an lr(OH), layer, the insulating layer 158 is a Ta2Os layer, and the second EC layer 158 is a WO3 layer, thereby providing high-quality display characteristics. Finally, a third electrode layer as the data lines D(l) is formed of a transparent electrode. To improve the reliability of the panel overall, a passivation layer or a sealing resin film is formed, thereby completing the panel.

In the present invention, a switching element comprises an element which has reversible (free from hysteresis) but non-linear I-V characteristics as shown in Fig. 14. Therefore, the conventional drive method cannot be adopted.

Figure 16 shows an example of drive waveforms effective for an active matrix of non-linear elements having the threshold characteristics according to the present invention. A scanning signal (J) is supplied to the scanning electrode and has a selection time 161 assigned to each scanning signal and a non-selection time other than the time 161. The signal (J) is at a non-selection potential V0 in the non-selection time and is at a selection potential V0 + V, (VO = 0 in Fig. 16 for ease of understanding).Meanwhile, a data signal supplied to the data line takes a maximum potential V0 + V, or a minimum potential V0 - V, in accordance with the display content of a picture element connected to the scanning line assigned to each time interval. In the gradation mode, the data signal changes steplessly or in multi levels between the maximum and minimum potentials. In the non-gradation mode, the data signal takes either the maximum or minimum potential, as shown in Fig. 16. Since an EC element is a charge-accumulation type element, high-density multiplexing cannot be achieved unless respective picture elements are driven in such a manner that when a charge is injected into a given picture element, charges on the adjacent picture element are not inadvertently shifted. Thus, certain limitations are imposed on the respective potentials.First, when the voltage for injecting a charge in an EC element is represented by "v" and the threshold voltage of the non-linear element is represented by Vth, V, and V, must satisfy equation (1) below: V, + V,- V,h-= v (1) When the voltage "v" is written, the potential at the display electrode DE(I,J) is increased to a potential 163 given by a maximum potential "V, + V0 + v" by the level shift of the data signal.At this time, in to prevent a discharge between the potential 163 and the non-selection potential V0 of the scanning signal (J), the threshold voltage Vth of the non-linear element must satisfy the following condition (2)*: V, + v < Vth ... (2) Figure 16 illustrates the case wherein the voltage "v" is positive. However, the voltage "v" may be negative depending upon the configuration of the EC element.Thus, in general, condition (2)* can be rewritten as: V, ' | Vm - v ... (2) From equation (1) and inequality (2) above, the following condition (3) is derived: 2 | v I s If conditions (2) and (3) above are satisfied, the display content of any desired picture element can be changed without changing that of other picture elements.

Figure 17 shows another example of drive waveforms according to the present invention. The EC element shown in Fig. 15 is colored at 1.3 V and is bleached at -1.3 V Therefore, the display contents cannot be changed as required, unless voltages of opposite polarities are applied. In this embodiment, coloring phase 171 and bleach phase 172 are provided. The coloring phase 171 is the same as that shown in Fig. 16. In the bleach phase 172, the voltage "v" applied to the EC element is negative and the selection potential -V, is also negative. If it is assumed that the phases are inverted about the non-selection potential V,, the bleach phase is the same as the coloring phase. Therefore, conditions (2) and (3) can be satisfied independently for each of the coloring and bleach phases.Another limiting condition must be satisfied due to the presence of the two phases. More specifically, if the coloring potention "v" must be held as required even in the bleach phase, difference 174 between the selection potential -V, and the hold voltage represented by arrow 173 with reference to -V, + V0 must be below the threshold voltage. Since the arrow 173 has a maximum value of v, the following condition is derived: V, - (V, - v) S Vto ... (4) From relations (1) and (4), the following inequality (5) is obtained.

I vl V, To summarize, if a voltage of a single polarity can be used to drive the elements, the following conditions (a) and (b) must be satisfied to change the display content of any desired picture element: V, Vth I V1, v | ... (a) 2 1 v | ... v Va t ... (b) If a voltage having two polarities must be used to drive elements, the following condition (c) must be satisfied in addition to the conditions (a) and (b) in order to change the display content of any desired picture element: vIIV,I ...(c) An EC display device having the novel configuration and drive method as described in the above embodiments has the following advantages over the conventional device: First, the switching element has a high drive capacity.An a-Si PIN diode used in the embodiments has an ON current of about 50 A/cm2, and a drive capacity of about 1,000 times that of an MIM element, thus providing a practical device. Second, the switching element has a sufficiently low OFF current. In the device of the configuration of the present invention, the forward direction characteristics of a diode are utilized in the updating mode such as erase mode, and the reverse direction characteristics of a diode are utilized in the hold mode. Therefore, the rectification ratio of the diode corresponds to the ON/OFF ratio of the switch.

Curve 81 shown in Fig. 8 shows the I-V characteristics when an a-Si diode is used. In this case, the rectification ratio is about 108 to 10'0 which is considerably larger than that of an MIM element. In this manner, according to the present invention, stable display hold without any contrast change due to leakage current can be performed. Third, the manufacture of the diode according to the present invention is relatively easy. In order to manufacture a diode, 3 to 4 masks are generally required including an insulating interlayer. In contrast to this, the manufacture of a TFT type MOS transistor requires 5 masks or 7 to 8 masks when optical shielding must be provided. The manufacture of an MIM element requires 3 to 4 masks. Thus, diodes can be manufactured in a simpler manner than transistors.

The device of the present invention is an electrochromic display device of the active matrix type which is free from the problems with a conventional MOS transistor, i.e., small area and high cost; the problem with a TFT or MIM switching element, i.e., a low drive capacity; and a problem with an MIM element, i.e., unstable charge hold capacity.

The above embodiments of the present invention are described with reference to the case of an overall solid-type EC. However, the present invention is similarly applicable to a liquid-type EC.

Claims

1. An electrochromic display device having a plurality of scanning lines, a plurality of data lines and a plurality of picture elements addressed through said scanning and data lines, wherein each of said picture elements has an electrochromic display element and unidirectional elements for controlling a charge to be injected into said electrochromic display element.

2. An electrochromic display device as claimed in claim 1, wherein said unidirectional element comprises a diode.

3. An electrochromic display device as claimed in claim 1, wherein each of said picture elements comprises a single electrochromic display element, at least one first diode for injecting a negative charge into said electrochromic display element, and at least one second diode for injecting a positive charge into said electrochromic display element.

4. An electrochromic display element as claimed in claim 3, wherein one end of said electrochromic display element of each picture element of said picture elements is connected to said data line thereof, the other end of said electrochromic display element is connected to a forward direction terminal of said first diode and a reverse direction terminal of said second diode, a reverse direction terminal of said first diode is connected to a first scanning line, and a forward direction terminal of said second diode is connected to a second scanning line.

5. An electrochromic display device as claimed in claim 3, wherein one end of said electrochromic display element of each of said picture elements is connected to said scanning line corresponding thereto, the other end of said electrochromic display element is connected to a forward direction terminal of said first diode and to a reverse direction terminal of said second diode, a reverse direction terminal of said first diode is connected to a first data line, and a forward direction terminal of said second diode is connected to a second data line.

6. An electrochromic display device as claimed in claim 2, wherein said diode comprises an amorphous silicon thin film.

7. An electrochromic display device as claimed in claim 1, wherein one end of said electrochromic display element of said picture element is connected to said data line corresponding thereto, the other end of said electrochromic display element is connected to one end of a diode group consisting of a plurality of diodes which are connected in opposite directions, and the other end of said diode group is connected to said scanning line corresponding thereto.

8. An electrochromic display device as claimed in claim 1, wherein one end of said electrochromic display element of said picture element is connected to said scanning line corresponding thereto, the other end of said electrochromic display element is connected to one end of a diode group consisting of a plurality of diodes which are connected in opposite directions, and the other end of said diode group is connected to said data line corresponding thereto.

9. A method of driving an electrochromic display device having a plurality of scanning lines, a plurality of data lines and a plurality of picture elements addressed through said scanning and data lines, and each of said picture elements having an electrochromic display element and unidirectional elements for controlling a charge to be injected into said electrochromic display element, line-sequential scanning signals being supplied to said scanning lines, and data signals based on display contents being supplied to said data lines so as to inject charges in said electrochromic display elements and to update display states thereof, wherein said scanning signal and data signal are shown by drive waveforms which comprise a positive charge injection phase or a negative charge injection phase, each of the charge injection phases comprises a selection time and a non-selection time, said data signal supplied to said data line takes the potential of the " V" for a reference potential in each phase, said scanning signal supplied to said scanning line connected to a positive charge injection diode takes the higher selection potential than the "-V" in said selection time of said positive charge injection phase, said scanning signal takes the lower non-seiection potential than the "-V" in said non-selection time of said positive charge injecon phase, and said scanning signal takes the lower potential than the "-V", while, said scanning signal supplied to said scanning line connected to a negative charge injection diode takes the higher potential than the "+V" in said positive charge injection phase, said scanning signal takes the lower selection potential than the "+V" in said selection time of said negative charge injection phase, and said scanning signal takes the higher nonselection potential than the "+V" in said non-selection time of said negative charge injection phase.

10. A method of driving an electrochromic display device having a plurality of scanning lines, a plurality of data lines and a plurality of picture elements addressed through said scanning and data lines, and each of said picture elements having an electrochromic display element and unidirectional elements for controlling a charge to be injected into said electrochromic display element, line-sequential scanning signals being supplied to said scanning lines, and data signals based on display contents being supplied to said data lines so as to inject charges in said electrochromic display elements and to update display states thereof, wherein said scanning signal and data signal are shown by drive waveforms which comprise the positive charge injection phase or the negative charge injection phase, said scanning signal supplied to said scanning line takes the potential of the "+V" for a reference potential in each phase, said data signal supplied to said data line connected to said positive charge injection diode takes the potential corresponding to a display content in said positive charge injection phase, and said data signal takes the lower potential than the "-V" in said negative charge injection phase, while, said data signal supplied to said data line connected to said negative charge injection diode takes the potential corresponding to a display content in said negative charge injection phase, and said data signal takes the higher potential than the "+V" in said positive charge injection phase.

11. A method of driving an electrochromic display device having a plurality of scanning lines, a plurality of data lines, and unit picture elements arranged at intersections of said scanning and data lines, said unit picture element comprising series circuits of electrochromic display elements and non-linear elements having a threshold voltage Vth, line-sequential scanning signals being supplied to said scanning lines, and data signals based on display contents being supplied to said data lines so as to inject charges in said electrochromic display elements and to update display states thereof, wherein when a non-selection potential of the scanning signal with reference to an applied voltage "v" of said electrochromic display element is presented by V,, a selection potential is represented by V0 + V,, and a data signal has a potential between a maximum potential V0 + V, and a minimum potentials V0 - V, based on the display contents, potentials V0 and V, satisfy: V, < I Vth - v I ... (a) 2 f v v < 1 V, t .. (b)

12. A method as claimed in claim 11, wherein the potential V0 further satisfies: I v I c VC ... (c)

13. A method as claimed in claim 11, wherein said non-linear element comprises a plurality of diodes which are connected in opposite directions and in parallel with each other.

14. An electrochromic display device constructed, arranged and adapted to operate substantially as herein described with reference to Figs. 4 to 8, Figs. 9 to 11 or Figs. 12 to 17 of the accompanying drawings.

15. A method of driving an electrochromic display device substantially as herein described with reference to Figs. 4 to 8, Figs. 9 to 11 or Figs. 12 to 17 of the accompanying drawings.