This application claims priority to Chinese patent application No. 202010092739.5 filed with the CNIPA on Feb. 14, 2020, disclosure of which is incorporated herein by reference in its entirety.
The present application relates to the field of display technology and, for example, to a pixel circuit, a method for driving the pixel circuit, and a display panel.
A Micro Light Emitting Diode (Micro-LED) display apparatus has been paid more and more attention because of miniaturization of Light Emitting Diode (LED) and higher luminance, luminous efficiency and lower power consumption than an Organic Light Emitting Diode (OLED) display device.
The Micro-LED has low luminous efficiency in a case of working at low current density. The luminous wavelength is different from that of high grayscale level, which causes the color shift of the display color of the Micro-LED display device apparatus. When the Micro-LED display apparatus displays, the Micro-LED display apparatus can be driven to emit light by using a pulse-width modulation (PWM) signal and digital driving mode through a power supply, thus improving the color shift problem. Thus, the data signal and the PWM signal of the power supply need to be synchronized accurately, which made the design of the driving circuit for Micro-LED very complicated.
The present application provides a pixel circuit, a method for driving a pixel circuit and a display panel to reduce the design complexity of the driver circuit to improve the color shift problem.
In the first aspect, embodiments of the present application provide a pixel circuit including a data write module, a storage module, a drive module, and a light emitting device.
The drive module includes a first control terminal and a second control terminal. The data write module is configured to write, at a data write stage, a data signal into the first control terminal of the drive module, the storage module is configured to maintain a potential of the first control terminal, the second control terminal is electrically connected to a PWM signal input terminal of the pixel circuit, and at a light emission stage, the second control terminal is configured to control the drive module to provide discontinuous current according to a PWM signal input from the PWM signal input terminal, and the light emitting device emits light in response to the discontinuous drive current.
In the second aspect, embodiments of the present disclosure further include a method for driving a pixel circuit. The pixel circuit includes a data write module, a storage module, a drive module and a light emitting device, where the drive module includes a first control terminal and a second control terminal. The method includes steps described below.
At a data write stage, the data write module of the pixel circuit writes a data signal into a first control terminal of the drive module of the pixel circuit, and the storage module maintains a voltage of the first control terminal of the drive module.
At a light emission stage, the second control terminal of the drive module controls the drive module to provide discontinuous drive current according to a PWM signal input from a PWM signal input terminal, and the light emitting device emits light in response to the discontinuous drive current.
In a third aspect, embodiments of the present application further provide a display panel including the pixel circuit of any embodiments of the present application.
An embodiment of the present application provides a pixel circuit.
Exemplarily, the first control terminal 131 of the drive module 130 receives a data signal at the data write stage, and maintains the data voltage of the first control terminal 131 through the storage module 120. The second control terminal 132 inputs the PWM signal of Vpwm. The PWM signal has a first level and a second level. The first level of the PWM signal and the second level of the PWM signal directly affect the transfer characteristic curve of the drive module 130, so that the drive module 130 is in turned on or turned off respectively when the PWM signal outputs different levels. Exemplarily, the drive module 130 may include a dual-gate N-type transistor.
Vgate2 is a voltage applied to the top gate, CACT is a capacitor when the active layer is drained, CGI2 is a capacitor of the second gate insulation layer, and CGI1 is a capacitor of the first gate insulation layer. Thus, the charge coupling effect between the bottom gate 402 and the top gate 406 is indicated when a channel of the dual-gate N-type transistor is completely drained.
Table 1 shows the material and thickness of various film layers of the dual-gate N-type transistor. On this basis, different constant bias voltages are applied to the top gate of the dual-gate N-type transistor, and the change of the transfer curve of the dual-gate N-type transistor is tested.
Table 2 shows the material and thickness of various film layers of another dual-gate N-type transistor. The difference from Table 1 is that the thickness of the second gate insulation layer is 500 nm.
Table 3 shows the material and thickness of various film layers of another dual-gate N-type transistor. The difference from Table 1 is that the thickness of the first gate insulation layer is 150 nm.
Table 4 shows the material and thickness of various film layers of another dual-gate N-type transistor. The difference from Table 1 is that the first gate insulation layer is made of SiNx/SiO2 material.
Table 5 shows the material and thickness of various film layers of another dual-gate N-type transistor. The difference from Table 1 is that the material of the first gate insulation layer is CYTOP with the thickness of 300 nm, the thickness of the active layer is 20 nm, and the material of the second gate insulation layer is polydimethylsiloxane (PDMS) with the thickness of 600 nm.
When the drive module 130 includes the dual-gate N-type transistor, the first control terminal 131 is the first gate, and the second
d control terminal 132 is the second gate. The data voltage is written into the first gate, and the PWM signal is written into the second gate.
IOLED is the current flowing through the dual-gate N-type transistor, μ is the carrier mobility of the dual-gate N-type transistor, W and L are a channel width of the dual-gate N-type transistor and a channel length of the dual-gate N-type transistor, respectively, VGS is the voltage difference between the gate of the dual-gate N-type transistor and the source of the double-gate N-type transistor, and VTH is the threshold voltage of the dual-gate N-type transistor.
When the PWM signal is output at a low level, the threshold voltage of the dual-gate N-type transistor shifts in a positive direction, that is, the threshold voltage of the dual-gate N-type transistor increases, so that the threshold voltage of the dual-gate N-type transistor is greater than the voltage difference between the gate of the dual-gate N-type transistor and the source of the dual-gate N-type transistor, the dual-gate N-type transistor is turned off, and a drive current is not connected, thereby the light emitting device 140 does not emit light. Therefore, it is possible to adjust the output time of the PWM signal at the high level by adjusting the duty cycle of the PWM signal, and then the light emitting time of the light emitting device 140 can be adjusted. When the light emitting time of the light emitting device 140 is adjusted through the duty cycle of the PWM signal, the first control terminal 131 of the drive module 140 maintains the data voltage, so that the data voltage does not need to be synchronized with the duty cycle of the light emitting device 140 controlled by the PWM signal, therefore, the design complexity of the driver circuit for driving the pixel circuit to work can be reduced, and then the manufacturing cost of the display panel can be reduced.
It is to be noted that the operation process of the dual-gate N-type transistor is exemplarily described above. In other embodiments, the drive module 130 may also include a dual-gate P-type transistor. When the PWM signal is output at high level, a threshold voltage of the dual-gate P-type transistor shifts in a positive direction, that is, the threshold voltage of the dual-gate P-type transistor increases, so that the threshold voltage of the dual-gate P-type transistor is greater than a voltage difference between a gate of the dual-gate P-type transistor and a source of the dual-gate P-type transistor, the dual-gate P-type transistor is turned off, and a drive current is not generated, thereby the light emitting device 140 does not emit light. When the PWM signal is output at a low level, a threshold voltage of the dual-gate P-type transistor shifts in a negative direction, that is, the threshold voltage of the dual-gate P-type transistor decreases, so that the threshold voltage of the dual-gate P-type transistor is smaller than a voltage difference between a gate of the dual-gate P-type transistor and a source of the dual-gate P-type transistor, the dual-gate P-type transistor is turned on, and a drive current is generated, thus driving the light emitting device 140 to emit light.
In addition, the luminance of the light emitting device 140 is the average luminance of the light emitting device 140 in one cycle of the PWM signal. For example, if the drive current flowing through the light emitting device 140 is I0, the corresponding luminance is L0, and if the duty cycle of the PWM signal is 11, the luminance L of the light emitting device 140 is L=L0*η. Therefore, the light emitting device 140 can be made to emit light with a stable color under the higher luminous efficiency. Then the average luminance of the light emitting device 140 is adjusted by adjusting the duty cycle η of the PWM signal, so that the average luminance of the light emitting device 140 is in a reasonable range, and the corresponding relationship between the luminance of the light-emitting device 140 and the grayscale level is satisfied. Exemplarily,
In a solution of this embodiment, the PWM signal is provided to the second control terminal of the drive module through the PWM signal input terminal, so that the drive module provides discontinuous drive current to the light emitting device, thereby controlling the light emitting time of the light emitting device. When the light emitting time of the light emitting device 140 is adjusted through the duty cycle of the PWM signal, the first control terminal of the drive module maintains the data voltage, so that the data voltage does not need to be synchronized with the duty cycle of the light emitting device controlled by the PWM signal, therefore, the design complexity of the driver circuit for driving the pixel circuit to work can be reduced, and then the manufacturing cost of the display panel can be reduced. At the same time, the light emitting device works in a drive current region with high luminous efficiency and stable light emitting color, and the luminance of the light emitting device corresponds to the low current and the low grayscale level through a PWM signal modulation, so that the luminance corresponding to different grayscale level can be satisfied when the light emitting device works in a region with high luminous efficiency and stable luminous color.
Exemplarily, referring to
At a data write stage, the data signal input from Vdata controlled by the Scan1 of the pixel circuit is written into the first control terminal 131 of the drive module 130 through the data write module 110, and the data signal of the first control terminal 131 is maintained through the storage module 120.
At a light emission stage, Scan1 of the pixel circuit controls the data write module 110 to stop writing the data voltage, and the PWM signal of Vpwm controls the drive module 130 to provide the discontinuous current, thereby controlling the light emitting time of the light emitting device 140.
Exemplarily,
At a first stage t1, scanl is at high level, the first transistor T1 is turned on, the data voltage is written into the gate of the drive transistor Tdr through the first transistor T1, and the data voltage is maintained through the storage capacitor Cst.
At a second stage t2, scanl is at high level, the first transistor T1 is turned off. At the same time, the first gate of the drive transistor Tdr is at the high level. When the pwm signal is at the high level, the drive transistor Tdr is turned on. When the pwm signal is the low level, the drive transistor Tdr is turned off. Therefore, the on time of the drive transistor Tdr is controlled by the duty cycle of the pwm signal, and the duty cycle of the pwm signal t can control the time when the drive transistor Tdr provides the drive current to the light emitting device 140, thereby controlling the light emitting time of the light emitting device 140.
It is to be noted that the drive current of the drive transistor Tdr is related to the value of the data voltage. As shown in
Exemplarily, the reset module 150 resets the anode of the light emitting device 140 while the data write module 110 writes the data voltage into the drive module 130, so as to avoid the residual voltage after the light emitting device 140 emits light in the previous frame affecting the luminance of the light emitting device 140 in the current frame.
Exemplarily, referring to
Exemplarily,
At a reset stage and the data write stage t3, scanl is at high level, the first transistor T1 and the second transistor T2 are turned on, the data voltage is written into the gate of the drive transistor Tdr through the first transistor T1, and the data voltage is maintained through the storage capacitor Cst. The reference signal vref input from the reference signal input terminal Vref is written to the anode of the light emitting device 140 through the second transistor T2, and the light emitting device 140 is reset.
At the light emission stage t4, scanl is at high level, and the first transistor T1 and the second transistor T2 are turned off. At the same time, the first gate of the drive transistor Tdr is at the high level. When the pwm signal is at the high level, the drive transistor Tdr is turned on. When the pwm signal is at low level, the drive transistor Tdr is turned off. Therefore, the on time of the drive transistor Tdr is controlled by the duty cycle of the pwm signal, the duty cycle of the pwm signal can control the time when the drive transistor Tdr provides the drive current to the light emitting device 140, thereby controlling the light emitting time of the light emitting device 140.
Exemplarily, before the light emission stage, the sensing control signal turns on the sensor module 160, the current of the drive module 130 is output to ISENSE and is output to an external sensor circuit through ISENSE, and the external sensor circuit compensates the pixel circuit according to the current flowing through the drive module 130.
Exemplarily, referring to
Exemplarily,
At a reset stage and the data write stage t5, scanl is at high level, the first transistor T1 and the second transistor T2 are turned on, the data voltage is written into the gate of the drive transistor Tdr through the first transistor T1, and the data voltage is maintained through the storage capacitor Cst. The reference signal vref input from the reference signal input terminal Vref is written to the anode of the light emitting device 140 through the second transistor T2, and the light emitting device 140 is reset.
At the sensing stage T6, the sensing control signal sense output from the sensing control signal input terminal SENSE is at high level, the third transistor T3 is turned on, and the current of the drive transistor Tdr is output to the external sensing circuit through the third transistor T3. The external circuit adds a compensation signal to the data voltage through data processing, thereby improving the luminous uniformity of the whole display panel.
At the light emission stage t7, scanl is at high level, and the first transistor T1 and the second transistor T2 are turned off. At the same time, the first gate of the drive transistor Tdr is at the high level. When the pwm signal is at the high level, the drive transistor Tdr is turned on. When the pwm signal is at the low level, the drive transistor Tdr is turned off. Therefore, the on time of the drive transistor Tdr is controlled by the duty cycle of the pwm signal, the duty cycle of the pwm signal can control the time when the drive transistor Tdr provides the drive current to the light emitting device 140, thereby controlling the light emitting time of the light emitting device 140.
A method for driving a pixel circuit is further provided in the embodiment of the present application and used for driving the pixel circuit provided by various solutions.
In step S10, at a data write stage, the data write module of the pixel circuit writes a data signal into a first control terminal of the drive module of the pixel circuit, and the storage module maintains a voltage of the first control terminal of the drive module.
In step S20, at a light emission stage, the second control terminal of the drive module controls the drive module to provide discontinuous drive current according to a PWM signal input from a PWM signal input terminal, and the light emitting device emits light in response to the discontinuous drive current.
In the solution of this embodiment, at the data write stage, the data signal is written into the first control terminal of the drive module, and the storage module maintains the voltage of the first control terminal of the drive module, so that the voltage of the first control terminal is maintained at the data signal. Then at the light emission stage, the PWM signal is provided to the second control terminal of the drive module, so that the drive module provides discontinuous drive current to the light emitting device, thereby controlling the light emitting time of the light emitting device. When the light emitting time of the light emitting device 140 is adjusted through the duty cycle of the PWM signal, the first control terminal of the drive module maintains the data voltage, so that the data voltage does not need to be synchronized with the duty cycle of the light emitting device controlled by the PWM signal, therefore, the design complexity of the driver circuit for driving the pixel circuit to work can be reduced, and then the manufacturing cost of the display panel can be reduced. At the same time, the light emitting device works in a drive current region with high luminous efficiency and stable light emitting color, and the luminance of the light emitting device corresponds to the low current and the low grayscale level through a PWM signal modulation, so that the luminance corresponding to different grayscale levels can be satisfied when the light emitting device works in a region with high luminous efficiency and stable luminous color.
An embodiment of the present application further provides a display panel.
Referring to
Exemplarily, the PWM signal line 210 is configured to output a PWM signal to provide the PWM signal to the PWM signal input terminal of the pixel circuit. The output terminal 221 of the gate driver circuit 220 is electrically connected to the scanning signal input terminal of the pixel circuit 101 through the scan line to provide a scanning signal to the pixel circuit 101 line by line, and the pixel circuit 101 is driven line by line. The output terminal 231 of the data driver Circuit 230 is electrically connected to the data signal input terminal of the pixel circuit 101 through the data signal line to provide the data signal to the pixel circuit 101. The pixel circuit 101 can connected to a data signal line corresponding to and electrically connected to the pixel circuit 101 under the action of the scanning signal input from the scan line electrically connected to the pixel circuit 101, and the data signal line transmits the data signal to the corresponding pixel driver circuit 101, thereby achieving a display function of the display apparatus.
Number | Date | Country | Kind |
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202010092739.5 | Feb 2020 | CN | national |
Filing Document | Filing Date | Country | Kind |
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PCT/CN2020/103431 | 7/22/2020 | WO |