CN113487994A - Pixel circuit, display device and pixel compensation method - Google Patents
Pixel circuit, display device and pixel compensation method Download PDFInfo
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- CN113487994A CN113487994A CN202110666066.4A CN202110666066A CN113487994A CN 113487994 A CN113487994 A CN 113487994A CN 202110666066 A CN202110666066 A CN 202110666066A CN 113487994 A CN113487994 A CN 113487994A
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
- G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
- G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
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Abstract
The invention discloses a pixel circuit, display equipment and a pixel compensation method, relates to the technical field of display circuits, and is used for solving the problem that in the prior art, in a PAM + PWM combined driving mode for mu LED high-gray-scale display, a PWM part can only realize positive threshold compensation. The pixel circuit includes: the circuit comprises a first switch circuit, a second switch circuit, a first capacitor, a comparison circuit, a driving circuit and a light-emitting device. The second end of the first switch circuit is electrically connected with the first end of the first capacitor and the control end of the comparison circuit. The second end of the first capacitor is electrically connected with the second end of the comparison circuit. The second end of the second switch circuit is electrically connected with the first end of the comparison circuit and the control end of the driving circuit. The second end of the driving circuit is electrically connected with the light emitting device. The display device comprises the pixel circuit. The pixel compensation method applies the pixel compensation circuit.
Description
Technical Field
The invention relates to the technical field of display circuits, in particular to a pixel circuit, display equipment and a pixel compensation method.
Background
Compared with AMOLED (Active-matrix organic light-emitting diode, or Active-matrix organic light-emitting diode, in the full name of Chinese), the micro LED has the advantages of smaller size, faster response speed, higher light-emitting efficiency, stronger stability, longer service life and the like. Therefore, the field of display applications based on μ LEDs has been rapidly developed. In this field, oxide thin-film transistor (TFT) materials represented by Amorphous indium gallium zinc oxide (a-IGZO) have become important materials for large-sized active μ LED display due to advantages of low leakage, low manufacturing temperature, and low cost.
In the PAM + PWM (analog voltage modulation + digital pulse width modulation) driving method for μ LED high gray scale display in the prior art, a comparison transistor in a PWM part is compensated by adopting a diode connection method, and the compensation method can only realize positive threshold compensation and has great limitation.
Disclosure of Invention
The invention aims to provide a pixel circuit, a display device and a pixel compensation method, which are used for solving the problem that in the prior art, in a PAM + PWM combined driving mode aiming at mu LED high-gray-scale display, a PWM part can only realize positive threshold compensation.
In a first aspect, the present invention provides a pixel circuit comprising: the circuit comprises a first switch circuit, a second switch circuit, a first capacitor, a comparison circuit, a driving circuit and a light-emitting device. The second end of the first switch circuit is electrically connected with the first end of the first capacitor and the control end of the comparison circuit. The second end of the first capacitor is electrically connected with the second end of the comparison circuit. The second end of the second switch circuit is electrically connected with the first end of the comparison circuit and the control end of the driving circuit. The second end of the driving circuit is electrically connected with the light emitting device.
In the threshold compensation stage, the first switch circuit and the second switch circuit are turned on, and the first switch circuit is used for providing a control voltage to the control end of the comparison circuit so as to turn on the comparison circuit. The second switch circuit is used for providing a first voltage for the comparison circuit, and adjusting the potential of the second end of the comparison circuit through the first voltage so as to realize positive threshold voltage compensation or negative threshold voltage compensation of the comparison circuit and keep the light-emitting device stable in a light-emitting stage.
Compared with the prior art, the pixel circuit provided by the invention has the advantages that in the threshold compensation stage, after the first switch circuit is conducted, the control voltage is provided for the comparison circuit, so that the comparison circuit is in a conducting state. Meanwhile, the second switch circuit is conducted, and the second switch circuit provides the first voltage for the comparison circuit so as to adjust the potential of the second end of the comparison circuit. At this time, the first capacitor can keep the potential of the control end of the comparison circuit unchanged, so that when the potential of the second end of the comparison circuit is smaller than the potential of the control end of the comparison circuit, the positive threshold voltage compensation of the comparison circuit can be realized; when the potential of the second end of the comparison circuit is larger than the potential of the control end of the comparison circuit, the negative threshold voltage compensation of the comparison circuit can be realized. Based on this, in the comparative light-emitting stage, the accurate control of the light-emitting duration of the light-emitting device is realized, so that the light-emitting precision of the light-emitting device is higher, and the light-emitting device is more stable in the light-emitting stage.
In a second aspect, the present invention also provides a display device comprising the pixel circuit of the first aspect.
Compared with the prior art, the beneficial effects of the display device provided by the invention are the same as those of the pixel circuit described in the first aspect, and are not described herein again.
In a third aspect, the present invention further provides a pixel compensation method for a pixel circuit, which applies the pixel circuit described in the first aspect. The pixel compensation method comprises the following steps:
and in the threshold compensation stage, the first switch circuit and the second switch circuit are controlled to be opened, and the first switch circuit is used for providing a control voltage to the control end of the comparison circuit so as to open the comparison circuit.
And controlling the second switch circuit to provide a first voltage for the comparison circuit, wherein the first voltage is used for adjusting the potential of the second end of the comparison circuit so as to realize positive threshold compensation or negative threshold compensation of the comparison circuit and keep the light-emitting device stable in a light-emitting stage.
Compared with the prior art, the pixel compensation method provided by the invention has the beneficial effects that
The beneficial effects of the pixel circuits are the same, and are not described herein.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a current-voltage transfer curve for a prior art μ LED;
FIG. 2 is a timing diagram of a PWM driving method for high gray scale display of a μ LED in the prior art;
FIG. 3 is a circuit diagram of a PWM + PAM driving method for high gray scale display of a μ LED in the prior art;
FIG. 4 is a first block diagram of a pixel circuit according to an embodiment of the present invention;
FIG. 5 is a timing diagram of control signals of a pixel circuit according to an embodiment of the present invention;
FIG. 6 is a state diagram of a pixel circuit in an initialization phase according to an embodiment of the present invention;
FIG. 7 is a state diagram of a pixel circuit in the threshold compensation stage according to an embodiment of the present invention;
fig. 8 is a second structural diagram of a pixel circuit according to an embodiment of the present invention;
FIG. 9 is a state diagram of a pixel circuit in a data input stage according to an embodiment of the present invention;
fig. 10 is a state diagram of the pixel circuit in the comparative light-emitting stage according to the embodiment of the invention.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or be indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or be indirectly connected to the other element.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise. The meaning of "a number" is one or more unless specifically limited otherwise.
In the description of the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
Fig. 1 illustrates a current-voltage transfer curve for a prior art μ LED. Referring to fig. 1, since the IV characteristic curve of the light emitting device μ LED is very steep, that is, the light emitting device μ LED has a very small change amount of the two-pole voltage from the low gray-scale current to the high gray-scale current, the gray scale is difficult to be developed by the conventional analog voltage driving (PAM).
The limitation of the PAM driving scheme has brought about a wide range of digital Pulse Width Modulation (PWM) driving schemes. The PWM driving controls the brightness sensed by human eyes by controlling the time for which the light emitting device muled emits light. Under the condition of the same driving current and the same refresh frequency, the larger the proportion of the light-emitting time of the light-emitting device mu LED to the total refresh time is, the higher the brightness sensed by human eyes is. By this method, accurate control of gray scale brightness can be achieved.
Fig. 2 illustrates a timing diagram of a PWM driving manner for high gray scale display of the light emitting device μ LED in the related art. Referring to fig. 2, a driving control signal may be generated using a gate driver on board (GOA) circuit using a PWM driving method. The PWM driving method divides each frame display time into n subframes with equal proportion, each pixel unit needs to be turned on once in each subframe time, and the data voltage input by an IC (Integrated Circuit) at each time determines whether the light emitting device μ LED emits light in the time corresponding to the subframe.
At present, a driving mode combining PWM and PAM is gradually becoming an important method for solving the problem of μ LED display of an active light emitting device. Fig. 3 illustrates a circuit structure diagram of a PWM + PAM driving method for high gray scale display of a light emitting device μ LED in the prior art, and referring to fig. 3, the PWM driving method can achieve a higher gray scale, but the driving speed of the GOA circuit is limited, and when the resolution is higher, multiple turn-on results in that a longer part of time cannot be used for light emission, thereby limiting the improvement of the number of gray scales. In the existing PAM + PWM combined driving method, the comparison transistor 332 in the PWM part is compensated by adopting a diode connection method, but the compensation method can only realize the positive threshold voltage compensation of the comparison transistor 332, but cannot realize the threshold compensation of the depletion-type IGZO TFT (thin film transistor), and has great limitation.
In view of the above technical problems, embodiments of the present invention provide a pixel circuit, which is driven by a PAM + PWM combined driving method. Fig. 4 illustrates a first structural diagram of a pixel circuit according to an embodiment of the present invention. Referring to fig. 4, a pixel circuit provided in an embodiment of the present invention includes: the circuit comprises a first switch circuit, a second switch circuit, a first capacitor C2, a comparison circuit, a drive circuit and a light-emitting device mu LED. The second terminal of the first switch circuit is electrically connected to the first terminal of the first capacitor C2 and the control terminal of the comparator circuit. A second terminal of the first capacitor C2 is electrically connected to a second terminal of the comparison circuit. The second end of the second switch circuit is electrically connected with the first end of the comparison circuit and the control end of the driving circuit. And the second end of the driving circuit is electrically connected with the light-emitting device mu LED.
In the threshold compensation stage, the first switch circuit and the second switch circuit are turned on, and the first switch circuit is used for providing a control voltage to the control end of the comparison circuit so as to turn on the comparison circuit. The second switch circuit is used for providing a first voltage for the comparison circuit, and adjusting the potential of the second end of the comparison circuit through the first voltage so as to realize positive threshold voltage compensation or negative threshold voltage compensation of the comparison circuit and keep the light-emitting device stable in a light-emitting stage.
Compared with the prior art, the pixel circuit provided by the invention has the advantages that in the threshold compensation stage, after the first switch circuit is conducted, the control voltage is provided for the comparison circuit, so that the comparison circuit is in a conducting state. Meanwhile, the second switch circuit is conducted, and the second switch circuit provides the first voltage for the comparison circuit so as to adjust the potential of the second end of the comparison circuit. At this time, the first capacitor can keep the potential of the control end of the comparison circuit unchanged, so that when the potential of the second end of the comparison circuit is smaller than the potential of the control end of the comparison circuit, the positive threshold voltage compensation of the comparison circuit can be realized; when the potential of the second end of the comparison circuit is larger than the potential of the control end of the comparison circuit, the negative threshold voltage compensation of the comparison circuit can be realized. Based on this, in the comparative light-emitting stage, the accurate control of the light-emitting duration of the light-emitting device is realized, so that the light-emitting precision of the light-emitting device is higher, and the light-emitting device is more stable in the light-emitting stage.
In one possible implementation, referring to fig. 2, the pixel circuit may further include a third switching circuit. The third switch circuit is electrically connected between the second end of the first capacitor and the second end of the comparison circuit. The control ends of the first switch circuit, the second switch circuit and the third switch circuit are electrically connected with a first control signal end, the first end of the first switch circuit is electrically connected with a reference power supply end, and the first end of the second switch circuit is electrically connected with a first level signal end;
in the threshold compensation stage, the first control signal terminal is used for providing a first control signal to the control terminals of the first switch circuit, the second switch circuit and the third switch circuit so as to turn on the first switch circuit, the second switch circuit and the third switch circuit.
In one possible implementation, referring to fig. 4, the pixel circuit further includes a reset circuit. The control end of the reset circuit is electrically connected with the second control signal end, the first end of the reset circuit is electrically connected with the second level signal end, and the second end of the reset circuit is electrically connected with the second end of the first capacitor.
In the initialization stage, the first control signal terminal controls the third switch circuit to be turned off, and the second control signal terminal controls the reset circuit to be turned on, so as to initialize the first capacitor C2. Based on the initialization of the first capacitor C2, the compensation effect of the comparison circuit during the threshold compensation phase can be ensured.
In one possible implementation manner, referring to fig. 4, the pixel circuit further includes: a first input circuit, a second input circuit and a second capacitor C3.
The first end of the first input circuit is electrically connected with the pulse width modulation end, the second end of the first input circuit is electrically connected with the second end of the first capacitor C2, and the control end of the first input circuit is electrically connected with the third control signal end. The first end of the second input circuit is electrically connected with the analog voltage modulation end, the second end of the second input circuit is electrically connected with the control end of the driving circuit and the first end of the second capacitor C3, and the control end of the second input circuit is electrically connected with the third control signal end. The first end of the second capacitor C3 is electrically connected to the control end of the driving circuit, and the second end of the second capacitor C3 and the first end of the driving circuit are electrically connected to the first power terminal.
In the signal input stage, the first control signal end controls the first switch circuit, the second switch circuit and the third switch circuit to be turned off. The second control signal end controls the reset circuit to be turned off. The third control signal end controls the first input circuit and the second input circuit to be conducted, under the coupling effect of the first capacitor, the control end voltage of the comparison circuit is increased, the comparison circuit is turned off, and the voltage of the first end of the second input circuit is stored in the second capacitor C3.
In the comparative light-emitting stage, the third control signal end controls the first input circuit and the second input circuit to be turned off, and the storage voltage of the second capacitor drives the driving circuit to be turned on so as to enable the light-emitting device to emit light.
It should be understood that the second end of the second capacitor C3 may also be electrically connected to any other dc power supply terminal, and may be selected according to actual situations.
In one possible implementation, referring to fig. 4, the pixel circuit may further include a third capacitor C1 and a fourth switch circuit. The first end of the third capacitor is electrically connected with the fourth control signal end, and the second end of the third capacitor is electrically connected with the second end of the first capacitor. The first end of the fourth switch circuit is electrically connected with the first power supply end, the second end of the fourth switch circuit is electrically connected with the second end of the comparison circuit, and the control end of the fourth switch circuit is electrically connected with the fifth control signal end. The first end of the fourth switch circuit is electrically connected with the first power supply end, the second end of the fourth switch circuit is electrically connected with the second end of the comparison circuit, and the control end of the fourth switch circuit is electrically connected with the fifth control signal end.
In the comparative light-emitting stage, the fourth control signal end provides a fourth control signal from low to high or from high to low to the first end of the third capacitor, under the coupling action of the first capacitor and the third capacitor, the voltage of the first end of the first capacitor is gradually increased or decreased to enable the comparison circuit to be conducted, the fifth control signal end controls the fourth switch circuit to be conducted, the voltage of the first end of the comparison circuit is set to be the voltage of the first power supply end, the driving circuit is enabled to be closed, and the light-emitting device stops emitting light.
As can be seen from the above circuit structures, the pixel circuit provided in the embodiments of the present invention may include a first switch circuit, a second switch circuit, a third switch circuit, a fourth switch circuit, a reset circuit, a first input circuit, a second input circuit, a comparison circuit, a driving circuit, a first capacitor, a second capacitor, a third capacitor, and a light emitting device. The first switch circuit, the second switch circuit, the third switch circuit, the fourth switch circuit, the reset circuit, the first input circuit, the second input circuit, the comparison circuit and the driving circuit may be N-type transistors, but are not limited thereto. For example: the reset circuit is a transistor T1, the first switch circuit is a transistor T2, the second switch circuit is a transistor T3, the third switch circuit is a transistor T4, the fourth switch circuit is a transistor T8, the first input circuit is a transistor T6, the second input circuit is a transistor T7, the comparison circuit is a transistor T5, and the driving circuit is a transistor T9. The light emitting device may be a μ LED. The first switch circuit, the second switch circuit, the third switch circuit, the fourth switch circuit, the reset circuit, the first input circuit, the first capacitor and the third capacitor are PWM driving parts. The second input circuit, the driving circuit and the second capacitor form a PAM driving part.
The first control signal terminal outputs a first control signal SN, the second control signal terminal outputs a second control signal RESET, the third control signal terminal outputs a third control signal SNN, the fourth control signal terminal outputs a fourth control signal sweet, and the fifth control signal terminal outputs a fifth control signal EM. The fourth control signal sweet and the fifth control signal EM may be global control signals, and the first control signal SN, the second control signal RESET, and the third control signal SNN may be reusable control signals, that is: the first control signal SN of the current stage may serve as the third control signal SNN of the previous stage and the second control signal RESET of the next stage.
In a possible implementation manner, the second control signal RESET may also be used as a global signal to control all pixels to perform initialization simultaneously and then perform compensation and data input row by row.
The first level signal terminal outputs a high level control signal VGH, and the second level signal terminal outputs a low level control signal VGL.
The reference power supply terminal outputs a reference voltage Verf, and the first power supply terminal outputs a low voltage VSS. The pulse width modulation end outputs a pulse width modulation signal PWMD, and the analog voltage modulation end outputs an analog voltage modulation PAMD.
In one possible implementation manner, the pulse width modulation terminal PWMD is electrically connected to the first terminal of the first input circuit through a first data signal line, the analog voltage modulation terminal PAMD is electrically connected to the first terminal of the second input circuit through a first data signal line, and the pulse width modulation terminal PWMD and the analog voltage modulation terminal PAMD are configured to input electrical signals to the first input circuit and the second input circuit respectively at the same time period.
In one possible implementation, the pulse width modulation terminal PWMD is electrically connected to the first terminal of the first input circuit through a third data signal line, for inputting an electrical signal to the first input circuit for a first period of time; the analog voltage modulation terminal PAMD is electrically connected to the first terminal of the second input circuit through a third data signal line, and is configured to input an electrical signal to the second input circuit in a second period.
It is noted that the relationship between the high-level control signal VGH, the low-level control signal VGL and the low voltage VSS is: VGH > VSS > VGL. The relationship between the reference voltage Verf, the high-level control signal VGH, and the low voltage VSS is: VGH > Vref > VSS. The relationship between the pwm signal PWMD, the analog voltage modulation PAMD, and the low voltage VSS is: PAMD > VSS > PWMD.
Fig. 5 illustrates a timing diagram of control signals of a pixel circuit provided by an embodiment of the invention. Referring to fig. 5, the working process of the pixel circuit provided by the embodiment of the invention can be divided into an initialization stage, a threshold compensation stage, a data input stage and a comparison light-emitting stage. The circuit states at each stage will be described one by one.
Fig. 6 illustrates a state diagram of a pixel circuit provided by an embodiment of the invention in an initialization phase. Referring to fig. 5 and 6, in the initialization stage, the first control signal SN, the third control signal SNN, and the fifth control signal EM all have a low level, turning off the first switch circuit T2, the second switch circuit T3, the third switch circuit T4, the fourth switch circuit T8, the first input circuit T6, and the second output circuit T7. Meanwhile, since the first switching circuit T2 is turned off, the comparison circuit T5 is turned off; since the second switch circuit T3 is turned off, the driving circuit T9 is enabled. The second control signal RESET has a high level, turning on the RESET circuit T1. The fourth control signal sweet has a low level, the fifth control signal EM has a low level, and the light emitting device is turned off to prevent flicker. At this time, the potential of the second end of the first capacitor C2 is set to be the low level control signal VGL, that is, the first capacitor C2 is initialized, so that the compensation effect of the comparison circuit in the threshold compensation stage can be ensured.
It should be noted that, in the case that the compensation time of the threshold compensation stage is sufficient (for example, the compensation time is greater than 50 microseconds), the initialization stage may be omitted, which may be determined according to the actual situation.
Fig. 7 illustrates a state diagram of a pixel circuit in the threshold compensation phase according to an embodiment of the present invention. Referring to fig. 5 and 7, in the threshold compensation stage, the first control signal SN has a high level, and turns on the first switch circuit T1, the second switch circuit T3, and the third switch circuit T4. The first switch circuit T1 is turned on and the reference voltage Vref has a high level, turning on the comparison circuit T5. The second control signal RESET has a low level, turning off the RESET circuit. The third control signal SNN and the fifth control signal EM have low levels, so that the first input circuit T6, the second input circuit T7 and the fourth switch circuit T8 are all turned off. The fourth control signal sweet remains low. The fifth control signal EM has a low level, turning off the light emitting device. The second control signal RESET has a low level, turning off the RESET circuit T1. At this time, the second switch circuit charges the second terminal of the comparator circuit T5 and the second terminal of the first capacitor C2 until the comparator circuit T5 is turned off, and finally the voltage at the second terminal of the comparator circuit T5 is stabilized to Vref-Vth5, and the voltage at both ends of the first capacitor C2 is stabilized to Vth 5. Since the present invention compensates using the source follower configuration, the voltage of the second terminal of the comparison circuit T5 can be charged to a higher potential than the voltage of the control terminal of the comparison circuit T5, so that the compensation of the negative threshold voltage of the comparison circuit can be achieved. The threshold compensation process can ensure that the shift of the threshold voltage of the comparison circuit T5 does not affect the switch state of the first input circuit T6 in the following comparison lighting phase.
Fig. 8 illustrates a second structure diagram of the pixel circuit according to the embodiment of the present invention. In a possible implementation manner, referring to fig. 8, in the threshold compensation stage, in order to make the potential of the control terminal of the comparison circuit more stable and achieve a better threshold voltage compensation effect, the pixel circuit may further include a fourth capacitor C4 and a fifth switch circuit T10. The fourth capacitor C4 is electrically connected between the first capacitor C2 and the third switch circuit. The first terminal of the fifth switch circuit is electrically connected to the first terminal of the first switch circuit, the second terminal of the fifth switch circuit T10 is electrically connected to the second terminal of the first capacitor C2, and the control terminal of the fifth switch circuit is electrically connected to the fifth control signal.
Fig. 9 illustrates a state diagram of a pixel circuit provided by an embodiment of the invention in a data input stage. Referring to fig. 5 and 9, in the data input stage, the first control signal SN has a low level, turning off the first, second, and third switch circuits T2, T3, and T4. The third control signal SNN has a high level, turning on the first input circuit T6 and the second input circuit T7. At this time, the voltage of the second terminal of the first capacitor C2 is set to PWMD by Vref-Vth5, and the voltage of the first terminal of the first capacitor C2 becomes PWMD + Vth5 due to the coupling effect of the first capacitor C2. Since PWMD < VSS < Vref, the comparison circuit T5 is turned off. At this time, the voltage of the first terminal of the comparison circuit is set to PAMD and stored on the second capacitor C3.
Fig. 10 illustrates a state diagram of the pixel circuit provided by the embodiment of the invention in the comparative light-emitting stage. Referring to fig. 5 and 10, in the comparative light emitting phase, the third control signal SNN has a low level, turning off the first and second input circuits T6 and T7. The fifth control signal EM has a high level to turn on the fourth switching circuit T8, the voltage of the second terminal of the comparison circuit is set to VSS, and at the same time, the fifth control signal EM may set the anode of the light emitting device μ LED to a high level. At this time, the second capacitor C3 maintains the voltage of the first terminal of the comparison circuit T5 at PAWD. The size of the PAWD may control the driving current of the driving circuit T9, i.e. the brightness of the light emitting device μ LED. According to the saturation current formula of the transistor:
it can be obtained that in the comparative light emitting phase, the current of the light emitting device μ LED is:
wherein, mu and CoxAnd
respectively, the mobility, the gate dielectric capacitance per unit area and the channel width-to-length ratio of the driver circuit T9 are shown.
Referring to fig. 10, when the fourth control signal SWEEP gradually changes linearly from a low level to a high level, the voltage of the control terminal of the comparison circuit T5 gradually increases linearly by the capacitive coupling effect of the first capacitor C2 and the third capacitor C1. At this time, the voltage of the control terminal of the comparison circuit T5 can be expressed as:
VA＝PWMD+Vth5+ΔSWEEP。
at this time, the voltage of the second terminal of the comparator circuit T5 is VSS. At the beginning of the comparative light emission phase, VALess than VSS, therefore the comparator circuit T5 is turned off and the first terminal of the comparator circuit T5 remains at VAThe current of the light emitting device μ LED remains unchanged. As the fourth control signal SWEEP becomes larger, the voltage V of the control terminal of the comparison circuit T5AGradually greater than VSS + Vth5, i.e., PWMD + Δ SWEEP>VSS, the comparator T5 is turned on to transmit the low voltage VSS at the first power terminal to the first terminal D of the comparator T5, turning off the driver T9. At this time, the light emitting device μ LED stops emitting light.
In the comparison process, due to threshold voltage compensation, the comparison result is not influenced by the change of the threshold voltage of the comparison circuit T5, and the stability and the reliability of the comparison result are greatly improved.
It should be understood that "×" in fig. 6 to 10 indicates that the circuit is in an off state.
The operation process of the pixel circuit in four stages shows that the on time of the comparison circuit T5 can be controlled by controlling the magnitude of the pulse width modulation signal PWMD at the pulse width modulation end, and the on time of the comparison circuit T5 can control the level of the point D at the first end of the comparison circuit, so as to control the on time of the driving circuit T9, and finally realize the control of the light emitting time of the light emitting device μ LED. Based on this, the purpose of controlling the light emitting time of the light emitting device μ LED by the pulse width modulation signal PWM can be achieved. For example, the larger the value of the pulse width modulation signal PWMD, the longer the on time of the comparison circuit T5, the shorter the time for which the voltage at the first terminal D of the comparison circuit is maintained at the pulse width modulation signal PAMD, the shorter the on time of the drive circuit T9, and the shorter the light emitting time of the light emitting device μ LED. Therefore, the PAM driving mode and the PWM driving mode are successfully combined in the pixel circuit, the conversion from analog voltage to digital pulse width is carried out in the pixel circuit, the IC is compatible with the design of the traditional analog voltage driving circuit, the complexity is low, and the cost is greatly reduced. The PWM part can realize positive and negative threshold compensation for the comparison circuit T5, and greatly enhances the stability and reliability of the comparison result.
In summary, in the pixel circuit provided in the embodiment of the invention, the second switch circuit T3, the comparison circuit T5, the third switch circuit T4 and the first capacitor C2 are connected to form a source follower structure, so that in the threshold compensation stage, the voltage at the control end a of the comparison circuit T5 can be fixed, and the high voltage at the first end D of the comparison circuit T5 charges the second end B or C of the comparison circuit T5. Based on this, the threshold voltage of the comparison circuit T5 can be detected without being influenced by the positive and negative values of the threshold voltage of the comparison circuit, so that it is ensured that the light emitting brightness and the light emitting time of the light emitting device are not influenced by the threshold voltage of the comparison circuit T5 in the comparison light emitting phase, and the influence of the factors such as the gate bias voltage and the ambient temperature on the threshold voltage of the comparison circuit T5 is avoided, so that the comparison result drifts.
The embodiment of the invention also provides display equipment which comprises the pixel circuit in the technical scheme.
Compared with the prior art, the beneficial effects of the display device provided by the invention are the same as those of the pixel circuit in the technical scheme, and are not repeated herein.
The embodiment of the invention also provides a pixel compensation method of the pixel circuit, and the pixel circuit adopting the technical scheme is provided. The pixel compensation method comprises the following steps:
step S100: and in the threshold compensation stage, the first switch circuit and the second switch circuit are controlled to be opened, and the first switch circuit is used for providing a control voltage to the control end of the comparison circuit so as to open the comparison circuit.
Step S200: and controlling the second switch circuit to provide a first voltage for the comparison circuit, wherein the first voltage is used for adjusting the potential of the second end of the comparison circuit so as to realize positive threshold compensation or negative threshold compensation of the comparison circuit and keep the light-emitting device stable in a light-emitting stage.
Compared with the prior art, the pixel compensation method provided by the invention has the same beneficial effects as the pixel circuit in the first aspect, and details are not repeated here.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (10)
1. A pixel circuit, comprising: the circuit comprises a first switch circuit, a second switch circuit, a first capacitor, a comparison circuit, a drive circuit and a light-emitting device;
the second end of the first switch circuit is electrically connected with the first end of the first capacitor and the control end of the comparison circuit; the second end of the first capacitor is electrically connected with the second end of the comparison circuit; the second end of the second switch circuit is electrically connected with the first end of the comparison circuit and the control end of the driving circuit, and the second end of the driving circuit is electrically connected with the light-emitting device;
in a threshold compensation stage, the first switch circuit and the second switch circuit are turned on, the first switch circuit is used for providing a control voltage to a control end of the comparison circuit to turn on the comparison circuit, the second switch circuit is used for providing a first voltage to the comparison circuit, and the potential of a second end of the comparison circuit is adjusted through the first voltage to realize positive threshold voltage compensation or negative threshold voltage compensation on the comparison circuit, so that the light-emitting device is kept stable in a light-emitting stage.
2. The pixel circuit according to claim 1, further comprising: the third switch circuit is electrically connected between the second end of the first capacitor and the second end of the comparison circuit;
the control ends of the first switch circuit, the second switch circuit and the third switch circuit are electrically connected with a first control signal end, the first end of the first switch circuit is electrically connected with a reference power supply end, and the first end of the second switch circuit is electrically connected with a first level signal end;
in the threshold compensation stage, the first control signal terminal is used for providing a first control signal to the control terminals of the first switch circuit, the second switch circuit and the third switch circuit, so as to turn on the first switch circuit, the second switch circuit and the third switch circuit.
3. The pixel circuit according to claim 2, further comprising: a reset circuit;
the control end of the reset circuit is electrically connected with the second control signal end; the first end of the reset circuit is electrically connected with the second level signal end, and the second end of the reset circuit is electrically connected with the second end of the first capacitor;
in an initialization stage, the first control signal terminal controls the third switch circuit to be turned off, and the second control signal terminal controls the reset circuit to be turned on, so that the first capacitor is initialized.
4. The pixel circuit according to any one of claims 1 to 3, further comprising: the first input circuit, the second input circuit and the second capacitor;
the first end of the first input circuit is electrically connected with the pulse width modulation end, the second end of the first input circuit is electrically connected with the second end of the first capacitor, and the control end of the first input circuit is electrically connected with the third control signal end;
the first end of the second input circuit is electrically connected with the analog voltage modulation end, the second end of the second input circuit is electrically connected with the control end of the driving circuit and the first end of the second capacitor, and the control end of the second input circuit is electrically connected with the third control signal end;
the first end of the second capacitor is electrically connected with the control end of the driving circuit, and the second end of the second capacitor and the first end of the driving circuit are electrically connected with a first power supply end;
in a signal input stage, the third control signal end controls the first input circuit and the second input circuit to be conducted, under the coupling effect of the first capacitor, the control end voltage of the comparison circuit is increased, the comparison circuit is turned off, and the voltage of the first end of the second input circuit is stored in the second capacitor.
5. The pixel circuit according to claim 4, wherein the pulse width modulation terminal is electrically connected to the first terminal of the first input circuit through a first data signal line, the analog voltage modulation terminal is electrically connected to the first terminal of the second input circuit through a first data signal line, and the pulse width modulation terminal and the analog voltage modulation terminal are configured to input an electrical signal to the first input circuit and the second input circuit, respectively, at the same time period;
and/or the pulse width modulation end is electrically connected with the first end of the first input circuit through a third data signal line and is used for inputting an electric signal to the first input circuit in a first period; the analog voltage modulation terminal is electrically connected with the first terminal of the second input circuit through a third data signal line and is used for inputting an electric signal to the second input circuit in a second period.
6. The pixel circuit according to claim 4, wherein during a comparative light emitting period, the third control signal terminal controls the first input circuit and the second input circuit to turn off, and the storage voltage of the second capacitor drives the driving circuit to turn on, so as to make the light emitting device emit light.
7. The pixel circuit according to claim 2, further comprising a third capacitor and a fourth switch circuit, wherein a first terminal of the third capacitor is electrically connected to a fourth control signal terminal, and a second terminal of the third capacitor is electrically connected to a second terminal of the first capacitor;
a first end of the fourth switching circuit is electrically connected with a first power supply end, a second end of the fourth switching circuit is electrically connected with a second end of the comparison circuit, and a control end of the fourth switching circuit is electrically connected with a fifth control signal end;
in a comparative light-emitting stage, the fourth control signal terminal provides a fourth control signal from low to high or from high to low to the first terminal of the third capacitor, under the coupling effect of the first capacitor and the third capacitor, the voltage of the first terminal of the first capacitor gradually increases or decreases to enable the comparison circuit to be switched on, the fifth control signal terminal controls the fourth switch circuit to be switched on, the voltage of the first terminal of the comparison circuit is set to the voltage of the first power supply terminal to enable the driving circuit to be switched off, and the light-emitting device stops emitting light.
8. The pixel circuit according to claim 2, wherein the pixel circuit further comprises a fourth capacitor and a fifth switch circuit;
the fourth capacitor is electrically connected between the first capacitor and the third switch circuit, the first end of the fifth switch circuit is electrically connected with the first end of the first switch circuit, the second end of the fifth switch circuit is electrically connected with the second end of the first capacitor, and the control end of the fifth switch circuit is electrically connected with a fifth control signal.
9. A display device comprising the pixel circuit according to any one of claims 1 to 8.
10. A pixel compensation method of a pixel circuit, characterized in that the pixel circuit of any one of claims 1 to 8 is applied; the pixel compensation method of the pixel circuit comprises the following steps:
in a threshold compensation stage, a first switch circuit and a second switch circuit are controlled to be opened, wherein the first switch circuit is used for providing a control voltage to a control end of the comparison circuit so as to open the comparison circuit;
and controlling the second switch circuit to provide a first voltage to the comparison circuit, wherein the first voltage is used for adjusting the potential of the second end of the comparison circuit so as to realize positive threshold compensation or negative threshold compensation on the comparison circuit and keep the light-emitting device stable in a light-emitting stage.
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