Pixel circuit, pixel driving method, and display device
A technology of pixel circuit and driving current, which is applied in the direction of static indicators, instruments, etc., can solve the problems of large driver chip area, low contrast of display panel, long gamma adjustment time, etc., and achieve the effect of avoiding false light emission
Inactive Publication Date: 2017-08-11
BOE TECH GRP CO LTD
8 Cites 30 Cited by
AI-Extracted Technical Summary
Problems solved by technology
In order to generate different data voltages, many sets of Gamma data are required, the amount of data processing is large, the area occupied by the driver chip is large, and the Gamma adjustment time when the display panel is shipped is also very long
[0003] In addition, in the existing pixel driving ...
Method used
In this embodiment, assuming that the luminous brightness produced by the light-emitting device OLED when the driving current flows into the light-emitting device OLED is L, the total time that the driving current flows into the current control module 2 and the total time that the driving current flows into the light-emitting device OLED in the light-emitting stage The time ratio is a:b, then the visual brightness of the light-emitting device OLED is thus visible, by adjusting the ratio of the total time the driving current flows into the current control module 2 during the light-emitting phase and the total time the driving current flows into the light-emitting device OLED, The adjustment of the visual brightness of the light-emitting device OLED can be realized.
It can be seen that the driving current of the driving transistor DTFT is related to the stable voltage Vref' and the data voltage Vdata provided by the fifth power supply terminal, and has nothing to do with the threshold voltage Vth of the driving transistor DTFT, so that the driving current flowing through the light-emitting device OLED can be avoided Affected by threshold voltage non-uniformity and drift.
[0085] In addition, it has been found in practical applications that although the fourth transistor T4 is in an off state, there will be a leakage current in the fourth transistor T4, which will drive the light-emitting device OLED to generate weak light, that is, the light-emitting device OLED will appear Problem with false lighting. To solve this problem, the present invention controls the second control signal to be at a low level, so that the seventh transistor T7 is turned on, so that the ground voltage is written into the first pole of the light-emitting device OLED, and at this time, the first pole of the light-emitti...
Abstract
The invention discloses a pixel circuit, a pixel driving method, and a display device. The pixel circuit comprises a driving transistor, a capacitor, a data writing module, and a current control module. In a luminous phase process, under control of a second control signal input by a second control signal input line, the current control module is used to control a ratio between total time of a driving current flowing to the current control module and the total time of the driving current flowing to a luminous device, and then the visual brightness of the luminous device is controlled. By adopting a technical scheme provided by the invention, when data voltage input by a data line is not changed, the current control module is used to adjust the ratio between the total time of the driving current flowing to the current control module and the total time of the driving current flowing to the luminous device, and therefore the adjustment of the visual brightness of the luminous device is realized. A number of Gamma data in a driving chip is effectively reduced, and the data processing speed of the driving chip is accelerated.
Application Domain
Static indicating devices
Technology Topic
Display deviceDriving current +3
Image
Examples
- Experimental program(4)
Example Embodiment
[0051] Example one
[0052] figure 1 This is a schematic diagram of the circuit structure of a pixel circuit provided in the first embodiment of the present invention, such as figure 1 As shown, the pixel circuit includes: a driving transistor DTFT, a capacitor C, a data writing module 1, a current control module 2, and a light emitting device OLED. The data writing module 1 is connected to the first terminal of the capacitor C, the second terminal of the capacitor C is connected to the control electrode of the driving transistor DTFT, the first electrode of the driving transistor DTFT is connected to the first power terminal, and the second terminal of the driving transistor DTFT Connected with the first pole of the light emitting device OLED, the current control module 2 is connected with the first pole and the second power terminal of the light emitting device OLED, and the second pole of the light emitting device OLED is connected with the second power terminal.
[0053] The data writing module 1 is used to write the data voltage provided by the data line Data to the first end of the capacitor C under the control of the first control signal input from the first control signal input line SC_1 during the data writing stage .
[0054] The driving transistor DTFT is used to generate a driving current under the control of the voltage at the second end of the capacitor C during the light-emitting phase.
[0055] The current control module 2 is used to control the total time of the driving current flowing into the current control module 2 and the driving current flowing into the light emitting device under the control of the second control signal input from the second control signal input line SC_2 during the light-emitting phase The ratio of the total time of the OLED to control the visual brightness of the light-emitting device OLED.
[0056] The working process of the pixel circuit provided in this embodiment will be described in detail below.
[0057] In the data writing phase, the data writing module 1 inputs a data voltage to the first terminal of the capacitor C, and at this time, the voltage of the second terminal of the capacitor C rises to a certain value through the bootstrap effect.
[0058] In the light-emitting phase, the driving transistor DTFT generates a driving current. According to the saturation driving current formula I of the driving transistor DTFT, it can be obtained:
[0059] I=K*(Vgs-Vth) 2
[0060] =K*(Vdata'-Vdd-Vth) 2
[0061] Among them, K is a constant, Vgs is the gate-source voltage of the driving transistor DTFT, Vth is the threshold voltage of the driving transistor DTFT, Vdd is the working voltage provided by the first power supply terminal, and Vdata' is the voltage of the second terminal of the capacitor C during the light-emitting phase Voltage.
[0062] During the entire light-emitting phase, the driving transistor DTFT will continue to output the driving current, and the magnitude of the driving current remains unchanged. The current control module 2 in the present invention can control the driving current to flow into the current control module 2 or flow into the light emitting device OLED under the control of the second control signal input from the second control signal input line SC_2.
[0063] Optionally, in this embodiment, the light-emitting stage includes: a number of alternately arranged light-emitting sub-stages and non-light-emitting sub-stages; the current control module 2 is specifically used to write the second voltage provided by the second power terminal during the non-light-emitting sub-stage Into the first pole of the light emitting device OLED, at this time the voltages of the first pole and the second pole of the light emitting device OLED (both are second voltages) are equal (there is no current between the first pole and the second pole of the light emitting device OLED) , The driving current flows into the current control module 2.
[0064] More specifically, in the non-light-emitting sub-phase, the driving current flows into the current control module 2, and no current flows through the light-emitting device OLED, and the light-emitting device OLED does not emit light; in the light-emitting sub-phase, the driving current flows into the light-emitting device OLED, Then the light emitting device OLED emits light. During the entire light-emitting phase, by controlling the ratio of the total time that the driving current flows into the current control module 2 to the total time that the driving current flows into the light-emitting device OLED, the visual brightness of the light-emitting device OLED can be adjusted.
[0065] In this embodiment, it is assumed that when the driving current flows into the light-emitting device OLED, the light-emitting brightness generated by the light-emitting device OLED is L, the ratio of the total time that the driving current flows into the current control module 2 in the light-emitting phase to the total time that the driving current flows into the light-emitting device OLED Is a:b, the visual brightness of the light-emitting device OLED is It can be seen that by adjusting the ratio of the total time that the driving current flows into the current control module 2 and the total time that the driving current flows into the light-emitting device OLED during the light-emitting phase, the visual brightness of the light-emitting device OLED can be adjusted.
[0066] It can be seen from the above that in the present invention, the ratio of the total time that the driving current flows into the current control module 2 and the total time that the driving current flows into the light-emitting device OLED can be adjusted under the condition that the data voltage does not change, so Realize the adjustment of the visual brightness of the light-emitting device OLED. Therefore, the technical solution of the present invention can effectively reduce the amount of Gamma data in the driver chip and increase the data processing speed of the driver chip.
[0067] Optionally, in this embodiment, the pixel circuit further includes: a reset module 3, a threshold compensation module 4, and a light emission control module 6. Among them, the reset module 3, the reset module 3 are connected to the first end of the capacitor C and the second end of the capacitor C, and the threshold compensation module 4 is connected to the second end of the capacitor C and the second pole of the driving transistor DTFT; light emission control module 6 is connected to the second pole of the driving transistor DTFT and the first pole of the light emitting device OLED.
[0068] The reset module 3 is used to reset the first end of the capacitor C and the second end of the capacitor C under the control of the reset control signal input from the reset control signal input line Reset during the reset stage.
[0069] The threshold compensation module 4 is used to combine the threshold voltage of the driving transistor DTFT and the first voltage provided by the first power terminal under the control of the first control signal input from the first control signal input line SC_1 during the threshold compensation stage Write to the second end of the capacitor C, thereby eliminating the influence of the drift of the threshold voltage of the driving transistor DTFT on the driving current.
[0070] The light emitting control module 6 is used to make the first electrode of the driving transistor DTFT and the first electrode of the light emitting device OLED conduct under the control of the light emitting control signal input from the light emitting control signal input line EM during the light emitting phase; and During the writing phase, the threshold compensation phase, and the reset phase, the second pole of the driving transistor DTFT and the first pole of the light emitting device OLED are disconnected, thereby preventing the driving current from flowing into the light emitting device OLED and causing the light emitting device OLED to emit light incorrectly.
[0071] Optionally, the pixel circuit further includes: a voltage stabilizing module 5, which is connected to the first end of the capacitor C; the voltage stabilizing module 5 is used to input the voltage on the third control signal input line SC_3 during the light-emitting phase Under the control of the third control signal, the fifth voltage provided by the fifth power terminal is written to the first terminal of the capacitor C to maintain the stability of the voltage at the first terminal of the capacitor C, thereby ensuring the voltage at the second terminal of the capacitor C The stability of the driving transistor DTFT effectively ensures the stability of the driving current output by the driving transistor DTFT in the light-emitting phase (the magnitude of the driving current remains unchanged).
[0072] The first embodiment of the present invention provides a pixel circuit, which can adjust the total time for the driving current to flow into the current control module during the light-emitting phase and the total time that the driving current flows to the light-emitting by the current control module under the condition that the data voltage input by the data line does not change. The ratio of the total time of the device, so as to realize the adjustment of the visual brightness of the light-emitting device. The technical scheme of the present invention can effectively reduce the amount of Gamma data in the drive chip and improve the data processing speed of the drive chip.
Example Embodiment
[0073] Example two
[0074] figure 2 This is a schematic diagram of the circuit structure of a pixel circuit provided in the second embodiment of the present invention, such as figure 2 As shown, the pixel circuit is an embodiment of the pixel circuit provided in the first embodiment. Wherein, optionally, the reset module 3 includes: a first transistor T1 and a second transistor T2, the control electrode of the first transistor T1 is connected to the reset control signal input line Reset, and the first electrode of the first transistor T1 is connected to the third power terminal Connected, the second electrode of the first transistor T1 is connected to the second terminal of the capacitor C, the control electrode of the second transistor T2 is connected to the reset control signal input line Reset, and the first electrode of the second transistor T2 is connected to the fourth power terminal, The second terminal of the second transistor T2 is connected to the first terminal of the capacitor C.
[0075] Optionally, the threshold compensation module 4 includes: a third transistor T3, the control electrode of the third transistor T3 is connected to the first control signal input line SC_1, the first electrode of the third transistor T3 is connected to the second end of the capacitor C, The second pole of the three transistor T3 is connected to the second pole of the driving transistor DTFT.
[0076] Optionally, the light emission control module 6 includes a fourth transistor T4, the control electrode of the fourth transistor T4 is connected to the light emission control signal input line EM, the first electrode of the fourth transistor T4 is connected to the first electrode of the driving transistor DTFT, The second pole of the four-transistor T4 is connected to the first pole of the light emitting device OLED.
[0077] Optionally, the voltage stabilizing module 5 includes: a fifth transistor T5, the control electrode of the fifth transistor T5 is connected to the third control signal input line SC_3, the first electrode of the fifth transistor T5 is connected to the fifth power terminal, and the fifth transistor The second pole of T5 is connected to the first terminal of the capacitor C.
[0078] Optionally, the data writing module 1 includes: a sixth transistor T6, the control electrode of the sixth transistor T6 is connected to the first control signal input line SC_1, the first electrode of the sixth transistor T6 is connected to the data line Data, and the sixth transistor The second pole of T6 is connected to the first end of the capacitor C.
[0079] Optionally, the current control module 2 includes: a seventh transistor T7, the control electrode of the seventh transistor T7 is connected to the second control signal line, the first electrode of the seventh transistor T7 is connected to the second power supply terminal, and the The second pole is connected to the first pole of the light emitting device OLED.
[0080] The working process of the pixel circuit provided in this embodiment will be described in detail below with reference to the accompanying drawings. Among them, the first power terminal provides a working voltage with a magnitude of Vdd; the second power terminal provides a ground voltage with a magnitude of Vss; the third power terminal provides a reset voltage with a magnitude of Vint; the fourth power terminal provides a reference voltage, Its size is Vref; the fifth power supply terminal provides a stable voltage whose size is Vref'; the threshold voltage of the driving transistor DTFT is Vth (when the driving transistor DTFT is a P-type transistor, Vth is generally a negative value); and the data voltage is Vdata.
[0081] image 3 for figure 2 The working timing diagram of the pixel circuit shown, such as image 3 As shown, the working process of the pixel circuit includes the following three stages: a reset stage t1, a data writing stage t2 (the threshold compensation stage and the threshold compensation stage are performed simultaneously), and a light-emitting stage t3.
[0082] In the reset phase t1, the reset control signal in the reset control signal input line Reset is at low level, the light emission control signal in the light emission control signal input line EM is at high level, and the first control signal is input to the first control signal in the line SC_1 At a high level, the second control signal in the second control signal input line SC_2 is at a low level, and the third control signal in the third control signal input line SC_3 is at a high level.
[0083] Since the reset control signal is at a low level, the first transistor T1 and the second transistor T2 are both turned on. At this time, the reset voltage is written to the second terminal of the capacitor C through the first transistor T1, and the voltage of the N1 node is Vint; the reference voltage is written to the first terminal of the capacitor C through the second transistor T2, and the voltage of the N2 node is Vref .
[0084] It should be noted that although there is a current output in the driving transistor DTFT at this time, since the light emission control signal is at a high level, the fourth transistor T4 is turned off, and the current output by the driving transistor DTFT cannot pass through the fourth transistor T4.
[0085] In addition, it is found in practical applications that although the fourth transistor T4 is in the off state, there will be a leakage current in the fourth transistor T4, which will drive the light-emitting device OLED to generate weak light, that is, the light-emitting device OLED may emit light incorrectly. problem. In order to solve this problem, the present invention controls the second control signal to be at a low level, so that the seventh transistor T7 is turned on, so that the ground voltage is written to the first pole of the light emitting device OLED. The voltage of one pole and the second pole are equal, and the leakage current generated in the fourth transistor T4 can only flow out through the seventh transistor T7, and cannot flow to the light-emitting device OLED, thereby effectively preventing the light-emitting device OLED from emitting light incorrectly.
[0086] In the data writing phase and the threshold compensation phase t2, the reset control signal in the reset control signal input line Reset is at high level, the light emission control signal in the light emission control signal input line EM is at high level, and the first control signal input line SC_1 The first control signal in the second control signal input line SC_2 is at a low level, and the third control signal in the third control signal input line SC_3 is at a high level.
[0087] Since the reset control signal is at a high level, the first transistor T1 and the second transistor T2 are both in an off state. At the same time, since the first control signal in the first control signal input line SC_1 is at a low level, the third transistor T3 and the sixth transistor T6 are both turned on, and the data voltage is written to the capacitor through the sixth transistor T6. At the first end of C, the potential of node N2 is Vdata; and since the third transistor T3 is turned on, the operating voltage starts to charge the node N1 through the driving transistor DTFT and the third transistor T3. When the voltage of node N1 is charged to Vdd+ At Vth, the driving transistor DTFT is turned off. At this time, there is a voltage difference Vdata-Vdd-Vth across the capacitor C.
[0088] It should be noted that in the process of charging the N1 node, although a leakage current will be generated in the fourth transistor T4, since the seventh transistor T7 remains in the on state, the leakage current will not flow into the light-emitting device OLED. In this stage, the light-emitting device OLED will not have the problem of false light emission.
[0089] At the light emission step t3, the reset control signal in the reset control signal input line Reset is at a high level, the light emission control signal in the light emission control signal input line EM is at a low level, and the first control signal is input to the first control signal in the line SC_1 At a high level, the third control signal in the third control signal input line SC_3 is at a low level.
[0090] It should be noted that, in this embodiment, the light-emitting phase t3 includes a number of light-emitting sub-phases t31 and non-light-emitting sub-phases t32 alternately arranged. Wherein, in the light-emitting sub-phase t31, the second control signal in the second control signal input line SC_2 is at a high level; in the non-light-emitting sub-phase t32, the second control signal in the second control signal input line SC_2 is at a low level Level.
[0091] In the light-emitting sub-phase t31, since the third control signal in the third control signal input line SC_3 is at a low level, the fifth transistor T5 is turned on, and the stable voltage Vref' is written to the first capacitor C through the fifth transistor T5. The voltage at the N2 node is Vref'. At the same time, since the reset control signal in the reset control signal input line Reset is at a high level and the first control signal in the first control signal input line SC_1 is at a high level, the first transistor T1 and the third transistor T3 are both Off, that is, the second terminal of the capacitor C is in a floating state. At this time, the capacitor C will produce a bootstrap effect to maintain the inconvenience of the voltage difference between the two ends of the capacitor C, and the voltage at the second end of the capacitor C jumps to Vdd+Vth+Vref'-Vdata.
[0092] According to the saturated driving current formula I of the driving transistor DTFT, we can get:
[0093] I=K*(Vgs-Vth) 2
[0094] =K*(Vdd+Vth+Vref'-Vdata-Vdd-Vth) 2
[0095] =K*(Vref'-Vdata) 2
[0096] It can be seen that the driving current of the driving transistor DTFT is related to the stable voltage Vref' and the data voltage Vdata provided by the fifth power terminal, and is not related to the threshold voltage Vth of the driving transistor DTFT, which can prevent the driving current flowing through the light emitting device OLED from being subject to the threshold voltage. Influence of unevenness and drift.
[0097] Because the second control signal in the second control signal input line SC_2 is at a high level, the seventh transistor T7 is turned off, and the driving current output by the driving transistor DTFT flows into the light-emitting device OLED, and the light-emitting device OLED starts to emit light. It should be noted that when the data voltage is a fixed value, the driving current output by the driving transistor DTFT is also a fixed value. At this time, the luminous brightness of the light-emitting device OLED under the action of the driving current can be measured through preliminary experiments. .
[0098] In the non-light emitting sub-phase t32, since the second control signal in the second control signal input line SC_2 is at a low level, the seventh transistor T7 is turned on, and the driving current output by the driving transistor DTFT flows out through the seventh transistor T7, and the light emitting device OLED does not emit light.
[0099] During the entire light-emitting phase, by controlling the ratio of the total time that the driving current flows into the current control module 2 to the total time that the driving current flows into the light-emitting device OLED, the visual brightness of the light-emitting device OLED can be adjusted. Specifically, by controlling the duty cycle of the second control signal, the ratio of the total time that the driving current flows into the current control module 2 and the total time that the driving current flows into the light-emitting device OLED can be controlled.
[0100] For the convenience of description, define a light-emitting sub-phase and a non-light-emitting sub-phase to form a light-emitting period. The second control signal is at a high level in the light-emitting sub-phase, and the second control signal is at a low level in the non-light-emitting sub-phase. If it is desired to realize the total time and driving current of the driving current flowing into the current control module 2 during the entire light-emitting phase The ratio of the total time flowing into the light-emitting device OLED is a:b, and the ratio of the time when the second control signal is at a low level to the time at a high level can be adjusted to a:b in one light-emitting period. The duty cycle of the control signal is
[0101] It should be noted that during the entire light-emitting phase, the light-emitting device OLED switches between the light-emitting state and the non-light-emitting state many times. Due to the fast switching frequency, the human eye will feel the light emission under the effect of the human eye's visual persistence. The device OLED is continuously emitting light, that is, the flicker of the light-emitting device OLED is not felt.
[0102] It can be seen from the above that in the pixel circuit provided by the present invention, the current control module 2 can not only adjust the visual brightness of the display device, but also can effectively avoid the non-light emitting phase (reset phase, data writing phase, threshold compensation phase). ) When the leakage current causes the display device to emit light incorrectly.
[0103] In the light-emitting phase t3, the voltage stabilizing module 5 continues to write a stable voltage to the first end of the capacitor C to stabilize the voltage value of the first end of the capacitor C, so that the voltage value of the second end of the capacitor C can be in a stable state In turn, the driving transistor DTFT can output a stable current, which is beneficial to the subsequent precise control of the visual brightness of the display device.
[0104] In this embodiment, preferably, the third control signal input line SC_3 and the light emission control signal input line EM are the same signal input line. In this case, the number of signal wirings in the pixel circuit can be reduced. The fifth power input terminal and the fourth power input terminal are the same power input terminal. In this case, the number of power ports in the pixel circuit can be reduced.
[0105] It should be noted that, considering that the second control signal used to control the operation of the current control module 2 should have a wider duty cycle adjustment range to control the display device to present different viewing angle brightness, the second control signal in this embodiment The input line SC_2 must be an independent and different from other signal input lines in the display circuit (the reset control signal input line Reset, the light emission control signal in the light emission control signal input line EM is at a high level, the first control signal input line SC_1, The signal routing of the third control signal input line SC_3).
[0106] The second embodiment of the present invention provides a pixel circuit, which can adjust the total time of the driving current flowing into the current control module and the driving current flowing into the light emitting phase through the current control module under the condition that the data voltage input by the data line does not change. The ratio of the total time of the device, so as to realize the adjustment of the visual brightness of the light-emitting device. The technical scheme of the present invention can effectively reduce the amount of Gamma data in the drive chip and improve the data processing speed of the drive chip.
Example Embodiment
[0107] Example three
[0108] Figure 4 This is a flowchart of a pixel driving method provided in the third embodiment of the present invention, such as Figure 4 As shown, the pixel driving method is based on a pixel circuit, and the pixel circuit adopts the pixel circuit in the first embodiment or the second embodiment. For the specific circuit structure, please refer to the description in the first and second embodiments above, and will not be repeated here. . The pixel driving method includes:
[0109] Step S1. In the data writing stage, the data writing module writes the data voltage provided by the data line to the first end of the capacitor under the control of the first control signal input from the first control signal input line.
[0110] Step S2. In the light-emitting phase, the driving transistor generates a driving current under the control of the voltage at the second end of the capacitor; the current control module controls the driving current to flow into the current under the control of the second control signal input from the second control signal input line The ratio of the total time of the control module to the total time of the driving current flowing into the light-emitting device is used to control the visual brightness of the light-emitting device.
[0111] Optionally, the light-emitting stage includes several light-emitting sub-stages and non-light-emitting sub-stages arranged alternately. Step S2 specifically includes:
[0112] Step S201: In the light-emitting sub-phase of the light-emitting phase, the current control module, under the control of the second control signal input from the second control signal input line, disconnects the second power terminal and the first pole of the light-emitting device, The driving current flows into the light emitting device, and the light emitting device emits light.
[0113] Step S202: In the non-light-emitting sub-phase of the light-emitting phase, the current control module writes the second voltage provided by the second power terminal to the light-emitting device under the control of the second control signal input from the second control signal input line The first pole of the LED, so that the driving current flows into the current control module to control the light-emitting device not to emit light.
[0114] For specific descriptions of the foregoing steps, refer to the corresponding content in the foregoing Embodiment 1 and Embodiment 2, which will not be repeated here.
PUM
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