A μLED unit circuit, light emitting control method and pixel device

Abstract

The present application relates to a μLED unit circuit, a light-emitting control method and a pixel circuit thereof, which belongs to the field of semiconductor technology and solves the problem that the existing GOA circuit has limited driving speed and that multiple openings when the resolution is high result in a longer period of time that cannot be used for light emission. The μLED unit circuit includes: a PWM signal generation circuit, a light-emitting control circuit and a μLED, wherein the PWM signal generation circuit generates a PWM signal with different pulse widths based on a light-emitting control signal and a comparison reference signal, and the comparison reference signal is a linearly decreasing ramp signal; the light-emitting control circuit includes a driving transistor, and the on-time of the driving transistor is controlled based on PWM signals with different pulse widths to provide a driving current; and the μLED controls the light-emitting time of the μLED based on the driving current. The combination of PAM and PWM driving modes within the pixel is realized, which is compatible with the traditional driving mode and satisfies the digital control of high grayscale.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a μLED unit circuit, a light emitting control method thereof, and a pixel device. Background Art

[0002] In recent years, due to the advantages of μLED over AMOLED (Active-matrix organic light emitting diode), such as smaller device size, faster response speed, higher luminous efficiency, stronger stability and longer service life, the display application field based on μLED has developed rapidly and attracted more and more attention. In this field, oxide thin film transistor (TFT, Thin Film Transistor) materials represented by amorphous indium gallium zinc oxide (a-IGZO) have become important materials for large-size active μLED displays due to their advantages such as transparency, bendability, low production temperature and low cost. At present, there are two most critical issues to be solved for active μLED display technology:

[0003] 1. μLED mass transfer technology: In order to reduce costs and maximize the advantages of μLED, μLED mass transfer technology is critical.

[0004] 2. Design of μLED grayscale expansion. Since the IV characteristic curve of μLED is very steep, that is, the change of the voltage between the two electrodes corresponding to the low grayscale current to the high grayscale current of μLED is very small, such as Figure 1 As shown, the gray scale is difficult to develop through the traditional analog voltage drive (PAM) method.

[0005] In the μLED display circuit based on n-type a-IGZO thin film transistors, most of the existing technologies use the traditional 2T1C pixel circuit with micro silicon-based CMOS driver to achieve high grayscale display (reference Figure 2 ). In addition, digital pulse width modulation (PWM) driving has also received widespread attention. PWM driving is to control the brightness perceived by the human eye by controlling the time the μLED emits light. Under the conditions of the same drive current and the same refresh frequency, the greater the proportion of the μLED light emission time to the total refresh time, the higher the brightness perceived by the human eye. In this way, precise control of grayscale brightness can be achieved (refer to Figure 3 ).

[0006] The above-mentioned prior art has the following technical defects: the active μLED display technology based on micro silicon-based CMOS drive is relatively expensive, and the use of PAM drive means that the drive circuit requires an extremely fast clock signal to meet the extremely high voltage resolution. At the same time, the use of CMOS drive has an adverse effect on the flexibility, transparency, and thickness of the panel. Using the PWM scheme, the drive control signal can be generated by the surface drive circuit (GOA). The PWM scheme divides each frame display time into n subframes of equal proportion. Each pixel unit needs to be turned on once in each subframe time. Each time the data voltage input by the IC determines whether the μLED emits light at the time corresponding to the subframe. This method can achieve a higher grayscale, but the GOA circuit driving speed is limited. When the resolution is high, multiple turns on result in a longer part of the time being unable to be used for light emission, thereby limiting the increase in the number of grayscales. Summary of the invention

[0007] In view of the above analysis, the embodiments of the present application aim to provide a μLED unit circuit, a light-emitting control method and a pixel device thereof, so as to solve the problem that the existing GOA circuit has limited driving speed. When the resolution is high, multiple activations result in a longer period of time that cannot be used for light emission, thereby limiting the improvement of the number of grayscale levels.

[0008] On the one hand, the embodiment of the present application provides a μLED unit circuit including: a PWM signal generating circuit, a light emitting control circuit and a μLED, wherein the PWM signal generating circuit is used to receive a light emitting control signal and a comparison reference signal and generate a PWM signal with different pulse widths based on the light emitting control signal and the comparison reference signal, wherein the comparison reference signal is a linearly decreasing ramp signal; the light emitting control circuit includes a driving transistor, which is used to receive the PWM signals with different pulse widths from the PWM signal generating circuit and control the on-time of the driving transistor based on the PWM signals with different pulse widths to provide a driving current; and the μLED is used to receive the driving current from the light emitting control circuit and control the light emitting time of the μLED based on the driving current. .

[0009] The beneficial effects of the above technical solution are as follows: According to the μLED unit circuit provided in the embodiment of the present application, through the circuit structure and working mode of the present application, the combination of PAM and PWM driving modes in the pixel can be realized, which is compatible with the traditional driving mode and meets the digital control of high grayscale. For 60Hz 2k resolution display applications, the modulatable luminous time of the present application can reach more than 75% of the entire refresh time, and 12bit grayscale can be achieved.

[0010] Based on further improvements of the above circuit, the PWM signal generating circuit includes a reset circuit, a compensation circuit and an inverter, wherein the reset circuit is used to receive a reset signal and initialize the μLED unit circuit; the inverter is connected to the output end of the reset circuit and is used to control the conduction of the transistor in the inverter based on the comparison between the input terminal voltage of the inverter and the power supply input terminal voltage to generate a PWM signal with different pulse widths; and the compensation circuit is used to compensate for the input terminal voltage of the inverter and the power supply input terminal voltage.

[0011] Based on further improvement of the above circuit, the reset circuit includes a first transistor, wherein the gate of the first transistor receives the reset signal, the source of the first transistor is connected to the reference power supply voltage, and the drain of the first transistor is connected to the input end of the inverter.

[0012] Based on the further improvement of the above circuit, the inverter includes a fourth transistor, a fifth transistor and a sixth transistor connected as an inverter, and the μLED unit circuit also includes a first capacitor, wherein the gate of the fourth transistor receives the light-emitting control signal, the source of the fourth transistor is connected to the first power supply voltage, and the drain of the fourth transistor is the power input terminal and connected to the source of the sixth transistor; the gate of the sixth transistor is the input terminal of the inverter and receives the comparison reference signal via the first capacitor, the drain of the sixth transistor is the output terminal of the inverter and connected to the source of the fifth transistor; and the gate of the fifth transistor receives the light-emitting control signal, and the drain of the fifth transistor is connected to the reference power supply voltage, wherein the first power supply voltage is less than the reference power supply voltage.

[0013] Based on further improvements of the above circuit, the compensation circuit includes a second transistor and a third transistor, wherein the gate of the second transistor is used to receive a row scan signal, the source of the second transistor is connected to the gate of the sixth transistor, and the drain of the second transistor is connected to the output end of the inverter; and the gate of the third transistor is used to receive the row scan signal, the source of the third transistor is connected to the drain of the fourth transistor and the source of the sixth transistor, and the drain of the third transistor receives a PWMD signal, wherein the PWMD signal is a voltage value that changes according to the luminous brightness of the μLED.

[0014] Based on further improvement of the above circuit, the light-emitting control circuit includes an edge improvement circuit and a driving circuit, wherein the edge correction circuit is used to receive the PWM signals of different pulse widths and the light-emitting control signal and correct the edge steepness of the PWM signals of different pulse widths; and the driving circuit is used to control the conduction time of the driving transistor based on the corrected PWM signals of different pulse widths to provide the driving current.

[0015] Based on further improvement of the above circuit, the edge correction circuit includes a seventh transistor, an eighth transistor and a second capacitor, wherein the gate of the seventh transistor is connected to the output end of the inverter and receives a second power supply voltage via the second capacitor, the source of the seventh transistor is connected to the drain of the eighth transistor, and the drain of the seventh transistor is connected to the drain of the ninth transistor; and the gate of the eighth transistor receives the light-emitting control signal, and the source of the eighth transistor receives the second power supply voltage.

[0016] Based on further improvements of the above circuit, the driving circuit includes the ninth transistor, the tenth transistor and the third capacitor, the tenth transistor being the driving transistor, wherein the gate of the ninth transistor receives the row scanning signal, the source of the ninth transistor receives the PAMD signal, and the PAMD signal is the voltage value when the luminous brightness is the highest; the source of the tenth transistor is connected to the second power supply voltage, the gate of the tenth transistor is connected to the drain of the seventh transistor and the drain of the ninth transistor; and one end of the third capacitor is connected to the second power supply voltage, and the other end of the third capacitor is connected to the drain of the seventh transistor and the drain of the ninth transistor, wherein the second power supply voltage is greater than the first power supply voltage and greater than the reference power supply voltage.

[0017] Based on further improvements of the above circuit, the cathode of the μLED is connected to the drain of the driving transistor and the anode of the μLED is used to receive the light control signal; or the anode of the μLED is connected to the drain of the driving transistor and the cathode of the μLED is used to receive a third power supply voltage.

[0018] Based on further improvement of the above circuit, the first transistor to the tenth transistor are N-type TFT transistors.

[0019] On the other hand, an embodiment of the present application provides a pixel device, comprising m×n μLED unit circuits according to the above embodiments.

[0020] On the other hand, an embodiment of the present application provides a μLED light-emitting control method, characterized in that it includes a comparative light-emitting step, wherein the comparative light-emitting step includes: generating PWM signals with different pulse widths based on a light-emitting control signal EM1 and a comparison reference signal SWEEP, wherein the comparison reference signal SWEEP is a linearly decreasing ramp signal; receiving the PWM signals with different pulse widths and controlling the on-time of a driving transistor based on the PWM signals with different pulse widths to provide a driving current; and receiving the driving current from the light-emitting control circuit and controlling the light-emitting time of the μLED based on the driving current.

[0021] Based on the further improvement of the above method, the driving current is:

[0022]

[0023] Among them, the μ, C ox and represents the mobility, unit area gate dielectric capacitance and channel width-to-length ratio of the driving transistor respectively, PAMD is the voltage value when the luminous brightness is the highest, V LED is the voltage of the μLED, and V th10 is the threshold voltage of the driving transistor.

[0024] Based on a further improvement of the above method, before the comparative light-emitting step, it also includes an initialization step and a row scanning step, wherein the initialization step initializes the μLED unit circuit of the pixel device based on the reset signal RESET; and the row scanning step, after the initialization step, scans the μLED unit circuit of the pixel device row by row based on the row scanning signal SN.

[0025] Based on a further improvement of the above method, the initialization step includes: providing the reset signal RESET to the gate of the first transistor T1, the first transistor T1 is turned on, so that the source of the first transistor T1 is connected to the reference power supply voltage REF to set the drain of the first transistor T1 to the reference power supply voltage REF, wherein the reset signal is a low level.

[0026] Based on a further improvement of the above method, the row scanning step includes: providing the row scanning signal SN to the gates of the second transistor T2 and the third transistor T3, the second transistor T2, the third transistor T3, and the sixth transistor T6 are turned on, so that the source of the sixth transistor T6 is connected to the PWMD signal via the third transistor T3 and is set to PWMD, and the drain of the sixth transistor T6 is connected to the gate of the sixth transistor T6 via the second transistor T2, so that the drain voltage of the sixth transistor T6 and the gate voltage of the sixth transistor T6 are PWMD-|V th6 |, wherein the PWMD signal is a voltage value that changes according to the luminous brightness of the μLED; providing a row scan signal SN to the gate of the ninth transistor T9, so that the ninth transistor T9 is turned on, so as to set the gate of the driving transistor to PAMD via the ninth transistor T9, wherein PAMD is a voltage value when the luminous brightness of the μLED is the highest, and the row scan signal SN is a low level.

[0027] Based on the further improvement of the above method, the comparison light emission step further includes: providing the light emission control signal EM1 to the gates of the fourth transistor T4 and the fifth transistor T5 and providing the comparison reference signal SWEEP to the gate of the sixth transistor T6 via the capacitor, turning on the fourth transistor T4, the fifth transistor T5 and the sixth transistor T6 and connecting them as an inverter, so that the source of the sixth transistor T6 is the power input terminal of the inverter and is connected to the first power supply voltage VGL via the fourth transistor T4, so that the voltage of the power input terminal of the inverter is the first power supply voltage VGL; the gate of the sixth transistor T6 is the input terminal of the inverter and the voltage of the power input terminal of the inverter is PWMD+V th6 -ΔSWEEP; the drain of the sixth transistor T6 is the output end of the inverter and is connected to the reference power supply voltage REF via the fifth transistor T5, so that the voltage at the output end of the inverter is at a high level and the seventh transistor T7 remains cut off, wherein the size of the sixth transistor T6 is larger than the size of the fifth transistor T5, and the light emitting control signal EM1 is a pulse signal.

[0028] Based on further improvement of the above method, the comparative light emission step further includes: turning on the driving transistor T10 so that the gate voltage of the driving transistor T10 maintains the PAMD signal, and the source of the driving transistor T10 is connected to the first power supply voltage VDD to provide the driving current so that the μLED starts to emit light.

[0029] Based on the further improvement of the above method, the comparison light-emitting step further comprises: when the comparison reference signal SWEEP is linearly increased so that the voltage PWMD+V th6 -ΔSWEEP is greater than VGH+V th6 When the sixth transistor T6 is turned off to raise the voltage of the output terminal of the inverter to REF, the seventh transistor T7 is turned on to transmit the first power supply voltage VDD to the gate of the driving transistor T10 or set the gate of the driving transistor T10 to the first power supply voltage VDD, and the driving transistor T10 is turned off so that the μLED stops emitting light.

[0030] Based on a further improvement of the above method, the light-emitting control signal EM2 is provided to the eighth transistor T8, the eighth transistor T8 and the driving transistor T10 are turned on, so that the gate voltage of the driving transistor T10 maintains the PAMD signal, and the source of the driving transistor T10 is connected to the first power supply voltage VDD to provide the driving current, so that the μLED starts to emit light, wherein the light-emitting control signal EM2 and the light-emitting control signal EM1 are pulse signals, and the rising edge of the light-emitting control signal EM2 lags behind the rising edge of the light-emitting control signal EM1.

[0031] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0032] 1. Through the circuit structure and working mode of this application, the combination of PAM (Pulse Amplitude Modulation) and PWM driving mode in the pixel can be realized, which is compatible with the traditional driving mode and meets the digital control of high grayscale. For 60Hz 2k resolution display applications, the modulatable luminous time of this application can reach more than 75% of the entire refresh time, and 12-bit grayscale can be achieved.

[0033] 2. The connection mode of T3, T2 and T6 forms a diode connection structure. In the Vth compensation stage, the source voltage of T6 is fixed, and the gate is discharged through T6, so that the threshold voltage of T6 can be detected, ensuring that the comparison light-emitting stage is independent of the threshold voltage of T6. This avoids the positive bias stress (PBS, Positive bias stress) caused by the positive bias voltage on the threshold voltage of T6, which causes the comparison result to drift.

[0034] 3. In the comparative luminescence stage, T4, T5 and T6 are connected as an inverter. By comparing the voltage between the input terminal of the inverter (point A) and the power input terminal (point D), PWM signals with different pulse widths can be generated at the output terminal of the inverter (point B).

[0035] 4. By controlling the size of the PWMD analog voltage value, the opening time of T6 can be controlled. The opening time of T6 can control the level of point B, thereby controlling the start time of T7, and then controlling the opening time of T10, and finally realizing the control of the light-emitting time of μLED and realizing PWM control of light-emitting brightness.

[0036] In the present application, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present application will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present application. The purpose and other advantages of the present application can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings are only for the purpose of illustrating specific embodiments and are not to be considered as limiting the present application. The same reference symbols denote the same components throughout the accompanying drawings.

[0038] Figure 1 The μLED current-voltage transfer curve obtained for the traditional analog voltage driving circuit.

[0039] Figure 2 It is an active μLED display for existing micro silicon-based CMOS.

[0040] Figure 3 It is a PWM driving solution for existing μLED high grayscale display.

[0041] Figure 4 1 is a circuit structure diagram and a timing diagram of a μLED unit circuit according to an embodiment of the present application.

[0042] Figure 5 is a circuit structure diagram of the initialization stage of the μLED unit circuit according to an embodiment of the present application.

[0043] Figure 6 is a circuit structure diagram of the row scanning stage (also called the data input compensation stage) of the μLED unit circuit according to an embodiment of the present application.

[0044] Figure 7 is a circuit structure diagram of a μLED unit circuit in a comparative light-emitting stage according to an embodiment of the present application.

[0045] Figure 8 is a timing diagram of different light emitting control signals of the μLED unit circuit according to an embodiment of the present application.

[0046] Fig. 9 1 is a PAM and PWM step-by-step input circuit diagram and a timing diagram of a μLED unit circuit according to an embodiment of the present application.

[0047] Fig.10 1 is a circuit structure diagram and a timing diagram of a μLED unit circuit according to an optional embodiment of the present application. DETAILED DESCRIPTION

[0048] The preferred embodiments of the present application are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present application and are used together with the embodiments of the present application to illustrate the principles of the present application, and are not used to limit the scope of the present application.

[0049] A specific embodiment of the present application discloses a μLED unit circuit, including a PWM signal generating circuit, a light emitting control circuit and a μLED. Figure 4 , the μLED unit circuit is described in detail.

[0050] refer to Figure 4 The PWM signal generating circuit is used to receive the light emitting control signal EM and the comparison reference signal SWEEP and generate PWM signals with different pulse widths based on the light emitting control signal EM and the comparison reference signal SWEEP, wherein the comparison reference signal SWEEP is a linearly decreasing ramp signal. The PWM signal generating circuit includes a reset circuit, a compensation circuit and an inverter, wherein the reference signal SWEEP is a linearly decreasing ramp signal. Figure 4 and Figure 5 , a reset circuit is used to receive a reset signal RESET and initialize the μLED unit circuit; reference Figure 4 and Figure 7 , an inverter connected to the output terminal of the reset circuit and used to control the conduction of the transistor in the inverter based on the comparison between the input terminal voltage of the inverter (i.e., point A) and the power input terminal voltage (i.e., point D) to generate a PWM signal with different pulse widths; and a reference Figure 4 and Figure 6, a compensation circuit is used to compensate the input terminal voltage of the inverter (i.e., point A) and the power input terminal voltage (i.e., point D). In an embodiment, the reset circuit includes a first transistor T1, wherein the gate of the first transistor T1 receives a reset signal RESET, the source of the first transistor T1 is connected to the reference power supply voltage REF, and the drain of the first transistor T1 (i.e., point A) is connected to the input terminal of the inverter. The inverter includes a fourth transistor T4, a fifth transistor T5 and a sixth transistor T6 connected as an inverter, and the μLED unit circuit also includes a first capacitor C1, wherein the gate of the fourth transistor T4 receives a light-emitting control signal EM, the source of the fourth transistor T4 is connected to the first power supply voltage VGL, and the drain of the fourth transistor T4 is the power input terminal (i.e., point D) and is connected to the source of the sixth transistor T6; the gate of the sixth transistor T6 is the input terminal of the inverter (i.e., point A) and receives the comparison reference signal SWEEP via the first capacitor C1, the drain of the sixth transistor T6 is the output terminal of the inverter (i.e., point B) and is connected to the source of the fifth transistor T5; and the gate of the fifth transistor T5 receives the light-emitting control signal EM, and the drain of the fifth transistor T5 is connected to the reference power supply voltage REF, wherein the first power supply voltage VGL is less than the reference power supply voltage REF. The compensation circuit includes a second transistor T2 and a third transistor T3, wherein the gate of the second transistor T2 is used to receive a row scan signal SN, the source of the second transistor T2 is connected to the gate of the sixth transistor T6, and the drain of the second transistor T2 is connected to the output end (i.e., point B) of the inverter; and the gate of the third transistor T3 is used to receive the row scan signal SN, the source of the third transistor T3 is connected to the drain of the fourth transistor T4 and the source of the sixth transistor T6, and the drain of the third transistor T3 receives a PWMD signal, wherein the PWMD signal is a voltage value that changes according to the light emitting brightness of the μLED. For example, the first transistor T1 to the sixth transistor T6 are N-type TFT transistors.

[0051] refer to Figure 4 The light emitting control circuit includes a driving transistor, namely, a tenth transistor T10, which is used to receive PWM signals of different pulse widths from a PWM signal generating circuit and control the on-time of the driving transistor based on the PWM signals of different pulse widths to provide a driving current. The light emitting control circuit includes an edge improvement circuit and a driving circuit, wherein the edge correction circuit is used to receive PWM signals of different pulse widths and a light emitting control signal EM and correct the edge steepness of the PWM signals of different pulse widths (refer to Figure 4The edge correction circuit includes a seventh transistor T7, an eighth transistor T8, and a second capacitor C2, wherein the gate of the seventh transistor T7 is connected to the output terminal of the inverter (i.e., point B) and receives the second power supply voltage VDD via the second capacitor C2, the source of the seventh transistor T7 is connected to the drain of the eighth transistor T8, and the drain of the seventh transistor T7 is connected to the drain of the ninth transistor T9 (i.e., point C); and the gate of the eighth transistor T8 receives the light emitting control signal EM, and the source of the eighth transistor T8 receives the second power supply voltage VDD. The driving circuit includes a ninth transistor T9, a tenth transistor T10 and a third capacitor C3, wherein the tenth transistor T10 is a driving transistor, wherein the gate of the ninth transistor T9 receives a row scanning signal SN, the drain of the ninth transistor T9 (i.e., point C) is connected to the drain of the seventh transistor T7, and the source of the ninth transistor T9 receives a PAMD signal, which is a voltage value when the luminous brightness is the highest; the source of the tenth transistor T10 is connected to a second power supply voltage VDD, the gate of the tenth transistor T10 is connected to the drain of the seventh transistor T7 and the drain of the ninth transistor T9 (i.e., point C); and one end of the third capacitor C3 is connected to the second power supply voltage VDD, and the other end of the third capacitor C3 is connected to the drain of the seventh transistor T7 and the drain of the ninth transistor T9, wherein the second power supply voltage VDD is greater than the first power supply voltage VGL and greater than the reference power supply voltage REF. For example, the seventh transistor T7 to the tenth transistor T10 are N-type TFT transistors.

[0052] refer to Figure 4 , the μLED is used to receive a driving current from the light emitting control circuit and control the light emitting time of the μLED based on the driving current. Figure 4 , the cathode of the μLED is connected to the drain of the driving transistor and the anode of the μLED is used to receive the light emission control signal EM. In an optional embodiment, reference Fig.10 The anode of the μLED is connected to the drain of the driving transistor T10 and the cathode of the μLED is used to receive the third power supply voltage VSS. For example, the driving transistor is an N-type TFT transistor.

[0053] Compared with the prior art, in the μLED unit circuit provided in this embodiment, through the circuit structure and working mode of this application, the combination of PAM (Pulse Amplitude Modulation) and PWM driving mode in the pixel can be realized, which is compatible with the traditional driving mode and meets the digital control of high grayscale. For 60Hz 2k resolution display applications, the modulatable luminous time of this application can reach more than 75% of the entire refresh time, and 12-bit grayscale can be achieved.

[0054] Another specific embodiment of the present application discloses a pixel device, including m×n μLED unit circuits described according to the above embodiments.

[0055] Another specific embodiment of the present application discloses a μLED light emission control method including an initialization step, a row scanning step, and a comparison light emission step. Figures 5 to 7 The μLED light emission control method is described in detail.

[0056] refer to Figure 5 , an initialization step, initializing the μLED unit circuit of the pixel device based on the reset signal RESET. In an embodiment, the initialization step includes: providing the reset signal RESET to the gate of the first transistor T1, turning on the first transistor T1, so that the source of the first transistor T1 is connected to the reference power supply voltage REF to set the drain of the first transistor T1 to the reference power supply voltage REF, wherein the reset signal RESET is at a low level.

[0057] refer to Figure 6 , a row scanning step, after the initialization step, scanning the μLED unit circuit of the pixel device row by row based on the row scanning signal SN. In an embodiment, the row scanning step includes: providing the row scanning signal SN to the gates of the second transistor T2 and the third transistor T3, the second transistor T2, the third transistor T3, and the sixth transistor T6 are turned on, so that the source of the sixth transistor T6 is connected to the PWMD signal via the turned-on third transistor T3 and is set to PWMD, and the drain of the sixth transistor T6 is connected to the gate of the sixth transistor T6 via the second transistor T2, so that the drain voltage of the sixth transistor T6 and the gate voltage of the sixth transistor T6 are PWMD-|V th6 |, wherein the PWMD signal is a voltage value that changes according to the luminous brightness of the μLED; the row scan signal SN is provided to the gate of the ninth transistor T9, so that the ninth transistor T9 is turned on, so as to set the gate of the driving transistor to PAMD via the ninth transistor T9, wherein PAMD is the voltage value when the luminous brightness of the μLED is the highest, and the row scan signal SN is at a low level.

[0058] refer to Figure 7 The comparison light-emitting step includes: generating PWM signals with different pulse widths based on the light-emitting control signal EM1 and the comparison reference signal SWEEP, wherein the comparison reference signal SWEEP is a linearly decreasing ramp signal; receiving PWM signals with different pulse widths and controlling the on-time of the driving transistor based on the PWM signals with different pulse widths to provide a driving current; and receiving the driving current from the light-emitting control circuit and controlling the light-emitting time of the μLED based on the driving current. The driving current is:

[0059]

[0060] Among them, μ, C ox and They represent the mobility of the driving transistor, the gate dielectric capacitance per unit area, and the channel width-to-length ratio, respectively. PAMD is the voltage value when the luminous brightness is the highest. V LED is the voltage of the μLED, and V th10 is the threshold voltage of the driving transistor T10.

[0061] refer to Figure 8 The comparison light-emitting step further includes: providing the light-emitting control signal EM1 to the gates of the fourth transistor T4 and the fifth transistor T5 and providing the comparison reference signal SWEEP to the gate of the sixth transistor T6 via the capacitor, turning on the fourth transistor T4, the fifth transistor T5 and the sixth transistor T6 and connecting them as an inverter, so that the source of the sixth transistor T6 is the power input terminal of the inverter (i.e., point A) and is connected to the first power supply voltage VGL via the fourth transistor T4, so that the voltage of the power input terminal of the inverter is the first power supply voltage VGL; the gate of the sixth transistor T6 is the input terminal of the inverter and the voltage of the power input terminal of the inverter (i.e., point D) is PWMD+V th6 -ΔSWEEP; the drain of the sixth transistor T6 is the output terminal of the inverter (i.e., point B) and is connected to the reference power supply voltage REF via the fifth transistor T5, so that the voltage at the output terminal of the inverter is at a high level and the seventh transistor T7 remains cut off, wherein the size of the sixth transistor T6 is larger than the size of the fifth transistor T5, and the light-emitting control signal EM1 is a pulse signal. The comparative light-emitting step further includes: turning on the driving transistor T10 so that the gate voltage of the driving transistor T10 maintains the PAMD signal, and the source of the driving transistor T10 is connected to the first power supply voltage VDD to provide a driving current so that the μLED starts to emit light. The comparative light-emitting step further includes: when the comparative reference signal SWEEP is linearly increased so that the voltage PWMD+V th6 -ΔSWEEP is greater than VGH+V th6When the sixth transistor T6 is turned off to raise the voltage of the output terminal of the inverter to REF, the seventh transistor T7 is turned on to transmit the first power supply voltage VDD to the gate of the driving transistor T10 or set the gate of the driving transistor T10 to the first power supply voltage VDD, and the driving transistor T10 is turned off so that the μLED stops emitting light.

[0062] refer to Figure 7 and Figure 8 , the light-emitting control signal EM2 is provided to the eighth transistor T8, the eighth transistor T8 and the driving transistor T10 are turned on, so that the gate voltage of the driving transistor T10 maintains the PAMD signal, and the source of the driving transistor T10 is connected to the first power supply voltage VDD to provide a driving current, so that the μLED starts to emit light, wherein the light-emitting control signal EM2 and the light-emitting control signal EM1 are pulse signals, and the rising edge of the light-emitting control signal EM2 lags behind the rising edge of the light-emitting control signal EM1.

[0063] refer to Figure 4 , the pixel device includes a plurality of rows of μLED unit circuits. Figure 4 and Figure 5 , the initialization step (1) in the timing diagram initializes multiple rows of μLED unit circuits at the same time. Figure 4 and Figure 6 , the row scanning step (2) in the timing diagram includes scanning the pixel device row by row, for example, the row scanning signal SN is provided to the first row to scan the first row, the row scanning signal SN+1 is provided to the second row to scan the second row, etc. The row scanning step includes performing row scanning (2), for example, the row scanning signal. Figure 4 and Figure 7 , the comparative light-emitting step (3) in the timing diagram controls the pixel device to emit light.

[0064] Fig. 9 The initialization step (1) is the same as Figure 4 and Figure 5 The initialization step (1) in is exactly the same. Fig. 9 Comparison of luminescence step (4) with Figure 4 and Figure 7 The comparative luminescence step (3) in is exactly the same. Fig. 9 The row scanning steps for each row of μLED unit circuits include Fig. 9 The PWAD input stage (2) in the figure sets point D to PWAD and the PAMD input stage (3) sets point C to PAMD. In addition, the time delay of SN relative to SNN is related to the number of scan lines, and the specific time is SN scan pulse width * number of scan lines. The time delay of SN+1 relative to SNN+1 is the same as the time delay of SN relative to SNN. Compared with Figure 4 The timing diagram in Fig. 9 The timing diagram in FIG. 1 sets point C to PAMD through additional row scanning signals SNN, SNN+1, etc. For example, SN and SNN are used for row scanning of the first row of μLED unit circuits. SN+1 and SNN+1 are used for row scanning of the first row of μLED unit circuits.

[0065] refer to Fig.10 In an optional embodiment, the anode of the μLED is connected to the drain of the driving transistor T10 and the cathode of the μLED is used to receive the third power supply voltage VSS. Fig.10 , the light emitting control signal EM is an inverted signal of the third power supply voltage VSS.

[0066] In the following, reference will be made to Figures 4 to 10 , the μLED light emission control method is described in detail by means of a specific example.

[0067] The present application provides a novel pixel circuit suitable for high grayscale μLED display, which combines PAM with PWM drive, performs analog voltage to digital pulse width conversion inside the pixel, and is compatible with traditional analog voltage drive circuit design. The IC has low complexity and greatly reduces the cost. The scanning signal can be realized through the GOA circuit, which only needs to be turned on once per frame time, and as much time as possible is used for light control. Compared with the prior art, the performance of the active μLED display circuit is further improved, and high grayscale display is further realized.

[0068] refer to Figure 4 The circuit of this application consists of three capacitors (C1, C2 and C3) and ten TFTs, of which T10 is a driving TFT to control the brightness of the μLED. The control signals are the reset signal RESET, the row scan signal SN, the light control signal EM and the comparison reference signal SWEEP, of which the EM and SWEEP signals are global signals, and the RESET and SN are multiplexed signals, that is, the current level SN signal can serve as the next level RESET signal. The high level of the control signal is VGH, and the low level is VGL. In addition, the power supply VDD (VGH>VDD>VGL), the reference voltage REF (VGH>REF>PWMD), the data signals PAMD and PWMD are required. The working mode can be divided into three stages:

[0069] Initialization phase

[0070] RESET is at a high level to turn on T1; SN is at a low level to turn off T2, T3 and T9; EM is at a low level to turn off T4, T5 and T8, and turn off the μLED to prevent flickering; the SWEEP signal remains at a high level, and the circuit state is as follows Figure 5 The voltage (VA) at point A is set to REF.

[0071] Data Input Compensation Phase

[0072] RESET goes low to turn off T1; SN goes high to turn on T2, T3, and T9. The voltage at point D (VD) is set to PWMD. T2 and T6 form a diode connection. VA discharges until T6 turns off. Eventually, VA and the voltage at point B (VB) stabilize at PWMD - V th6 ; T9 turns on, and the voltage at point C (VC) is set to PAMD. EM remains low to turn off T4, T5, and T8, and at the same time turns off the μLED to prevent flickering; the SWEEP signal remains high, as Figure 6 . The compensation process in this phase ensures that during the subsequent comparison and emission phase, the drift of the threshold voltage of T6 will not affect the switching state of T6.

[0073] Comparison and Emission Phase

[0074] RESET goes low to turn off T1; SN is low to turn off T2, T3, and T9; EM goes high to turn on T4, T5, and T8, and at the same time EM sets the anode of the μLED high, as Figure 7 . Due to the effect of the storage capacitor C3, VC always remains at PAMD. The magnitude of PAMD controls the drive current of T10, that is, controls the brightness of the μLED. According to the transistor saturation current formula:

[0075]

[0076] The current I in this phase can be obtained as: OLED The current magnitude is:

[0077]

[0078] where μ, C ox and represent the mobility of T10, the gate dielectric capacitance per unit area, and the channel width-to-length ratio respectively. The SWEEP signal starts to linearly change from high to low. Through the capacitive coupling effect of C1, VA gradually linearly decreases (VA = PWMD + V th - ΔSWEEP). The source voltage of T6 is VGL (VGL < PWMD + V th ). At the beginning of the comparison and emission phase, VA is greater than VGL, T6 turns on. The size of T6 is larger than that of T5, making VB low. T7 remains off, and the μLED current remains the above magnitude. As the SWEEP signal further decreases, VA gradually becomes less than VGL + V th , that is, PWMD - ΔSWEEP < VGL, B gradually rises to REF, thus turning on T7, transmitting VDD to point C, turning off T10, and the μLED stops emitting light. The above comparison node is independent of the threshold voltage of T6 and is only related to the magnitude of PWMD and the slope of SWEEP.

[0079] Through the above working process, it can be known that by controlling the size of the PWMD analog voltage value, the time when T6 is turned on can be controlled. The level of point B can be controlled during the T6 turn-on time, thereby controlling the start time of T7, and then controlling the turn-on time of T10, and finally realizing the control of the light-emitting time of the μLED, and achieving the purpose of PWM control of the light-emitting brightness. For example, the larger the PWMD, the longer the T6 turn-on time, the longer the B point maintains a low level, the shorter the T7 turn-on time, the longer the T10 turn-on time, and the longer the light-emitting time. Therefore, the pixel circuit successfully combines PAM with PWM to achieve grayscale expansion.

[0080] In addition, the above definitions of the various elements and methods are not limited to the various specific structures, shapes or methods mentioned in the embodiments.

[0081] 1. One end of C2 is connected to B, and the other end can be connected to VDD or any other DC power supply; one end of C3 is connected to C, and the other end can be connected to VDD or any other DC power supply.

[0082] 2. The rising edge of the T5 gate signal EM may affect the voltage increase at point B due to parasitic effects, thus causing T7 to be turned on incorrectly. In order to avoid the influence of point C, the above circuit uses T8 for protection. If the parasitic capacitance of the transistor is small and the panel parasitic effect is not obvious, T8 can be removed and the source of T7 can be directly connected to VDD.

[0083] 3. The rising edge of the T5 gate signal EM may affect the voltage at point B due to parasitic effects, thus causing T7 to turn on incorrectly, so T8 is needed for protection. The gate of T8 can directly use the EM signal, or use the EM2 signal with a longer pulse width than the low-level EM signal, to completely avoid the voltage change at point B under the influence of the EM rising edge from affecting point C, thus achieving better protection effect. The relationship between the two signals is as follows: Figure 8 shown.

[0084] 4. PAMD and PWMD can be input simultaneously through two data signal lines according to the above working process, or they can be input successively through one data signal line (DATA). The corresponding circuit diagram and timing diagram for sequential input are as follows: Fig. 9 shown.

[0085] 5. μLED can also adopt the structure of connecting the anode to T10 and introducing VSS control to the cathode to prevent flickering. The circuit structure and timing diagram are as follows: Fig.10 shown.

[0086] 6. The RESET signal that controls initialization can also be used as a global signal to control all pixels to be initialized at the same time and then perform data input compensation row by row.

[0087] 7. This application is also applicable to other n-type TFT devices.

[0088] In addition, since the manufacturing process of the N-type TFT transistor does not require a crystallization step and thus does not require high-cost crystallization process manufacturing equipment, the cost of the N-type TFT transistor is low and the N-type TFT transistor is suitable for small screens, such as tablet computers and monitors.

[0089] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0090] 1. Through the circuit structure and working mode of this application, the combination of PAM (Pulse Amplitude Modulation) and PWM driving mode in the pixel can be realized, which is compatible with the traditional driving mode and meets the digital control of high grayscale. For 60Hz 2k resolution display applications, the modulatable luminous time of this application can reach more than 75% of the entire refresh time, and 12-bit grayscale can be achieved.

[0091] 2. The connection mode of T3, T2 and T6 forms a diode connection structure. In the Vth compensation stage, the source voltage of T6 is fixed, and the gate is discharged through T6, so that the threshold voltage of T6 can be detected, ensuring that the comparison light-emitting stage is independent of the threshold voltage of T6. This avoids the positive bias stress (PBS, Positive bias stress) caused by the positive bias voltage on the threshold voltage of T6, which causes the comparison result to drift.

[0092] 3. In the comparative luminescence stage, T4, T5 and T6 are connected as an inverter. By comparing the voltage between the input terminal of the inverter (point A) and the power input terminal (point D), PWM signals with different pulse widths can be generated at the output terminal of the inverter (point B).

[0093] 4. By controlling the size of the PWMD analog voltage value, the opening time of T6 can be controlled. The opening time of T6 can control the level of point B, thereby controlling the start time of T7, and then controlling the opening time of T10, and finally realizing the control of the light-emitting time of μLED and realizing PWM control of light-emitting brightness.

[0094] Those skilled in the art will appreciate that all or part of the processes of the above-mentioned embodiments can be implemented by instructing related hardware through a computer program, and the program can be stored in a computer-readable storage medium, wherein the computer-readable storage medium is a disk, an optical disk, a read-only storage memory, or a random access memory, etc.

[0095] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed in the present application should be covered within the protection scope of the present application.

Claims

1. A μLED unit circuit, characterized in that: include: PWM signal generating circuit, light emitting control circuit and μLED, wherein: The PWM signal generating circuit is used to receive a light-emitting control signal and a comparison reference signal and generate a PWM signal with different pulse widths based on the light-emitting control signal and the comparison reference signal, wherein the comparison reference signal is a linearly decreasing ramp signal; The light emitting control circuit includes a driving transistor for receiving the PWM signals of different pulse widths from the PWM signal generating circuit and controlling the on-time of the driving transistor based on the PWM signals of different pulse widths to provide a driving current; and The μLED is configured to receive the driving current from the light emitting control circuit and control the light emitting time of the μLED based on the driving current, The light emitting control circuit includes an edge correction circuit and a driving circuit, wherein the edge correction circuit is used to receive the PWM signals with different pulse widths and the light emitting control signal and correct the edge steepness of the PWM signals with different pulse widths; and the driving circuit is used to control the on-time of the driving transistor based on the corrected PWM signals with different pulse widths to provide the driving current; Wherein, the edge correction circuit includes a seventh transistor, an eighth transistor and a second capacitor, wherein the gate of the seventh transistor is connected to the output end of the inverter in the PWM signal generating circuit and receives a second power supply voltage via the second capacitor, the source of the seventh transistor is connected to the drain of the eighth transistor, and the drain of the seventh transistor is connected to the drain of the ninth transistor; and the gate of the eighth transistor receives the light emitting control signal, and the source of the eighth transistor receives the second power supply voltage.

2. The μLED unit circuit according to claim 1, characterized in that: The PWM signal generating circuit comprises a reset circuit, a compensation circuit and the inverter, wherein: The reset circuit is used to receive a reset signal and initialize the μLED unit circuit; The inverter is connected to the output terminal of the reset circuit and is used to control the conduction of the transistor in the inverter based on the comparison between the input terminal voltage of the inverter and the power input terminal voltage to generate PWM signals with different pulse widths; and The compensation circuit is used to compensate the input terminal voltage of the inverter and the power input terminal voltage.

3. The μLED unit circuit according to claim 2, characterized in that: The reset circuit comprises a first transistor, wherein The gate of the first transistor receives the reset signal, the source of the first transistor is connected to a reference power supply voltage, and the drain of the first transistor is connected to an input terminal of the inverter.

4. The μLED unit circuit according to claim 3, characterized in that: The inverter includes a fourth transistor, a fifth transistor, and a sixth transistor connected as an inverter, and the μLED unit circuit also includes a first capacitor, wherein, The gate of the fourth transistor receives the light emitting control signal, the source of the fourth transistor is connected to the first power supply voltage, and the drain of the fourth transistor is the power supply input terminal and connected to the source of the sixth transistor; The gate of the sixth transistor is the input terminal of the inverter and receives the comparison reference signal via the first capacitor, and the drain of the sixth transistor is the output terminal of the inverter and connected to the source of the fifth transistor; and The gate of the fifth transistor receives the light emitting control signal, and the drain of the fifth transistor is connected to the reference power supply voltage, wherein the first power supply voltage is lower than the reference power supply voltage.

5. The μLED unit circuit according to claim 4, characterized in that: The compensation circuit includes a second transistor and a third transistor, wherein: The gate of the second transistor is used to receive a row scanning signal SN, the source of the second transistor is connected to the gate of the sixth transistor, and the drain of the second transistor is connected to the output end of the inverter; and The gate of the third transistor is used to receive the row scan signal SN, the source of the third transistor is connected to the drain of the fourth transistor and the source of the sixth transistor, and the drain of the third transistor receives a PWMD signal, wherein the PWMD signal is a voltage value that changes according to the luminous brightness of the μLED.

6. The μLED unit circuit according to claim 5, characterized in that: The driving circuit includes the ninth transistor, the tenth transistor and a third capacitor, the tenth transistor is the driving transistor, wherein: The gate of the ninth transistor receives the row scanning signal SN, and the source of the ninth transistor receives the PAMD signal, where the PAMD signal is a voltage value when the light emission brightness is the highest; A source of the tenth transistor is connected to the second power supply voltage, and a gate of the tenth transistor is connected to a drain of the seventh transistor and a drain of the ninth transistor; and One end of the third capacitor is connected to the second power supply voltage, and the other end of the third capacitor is connected to the drain of the seventh transistor and the drain of the ninth transistor, wherein the second power supply voltage is greater than the first power supply voltage and greater than the reference power supply voltage.

7. The μLED unit circuit according to any one of claims 1 to 6, characterized in that: The cathode of the μLED is connected to the drain of the driving transistor and the anode of the μLED is used to receive the light emitting control signal; or The anode of the μLED is connected to the drain of the driving transistor and the cathode of the μLED is used to receive a third power supply voltage.

8. The μLED unit circuit according to claim 6, characterized in that: The first transistor to the tenth transistor are N-type TFT transistors.

9. A pixel device, characterized in that: The method comprises m×n μLED unit circuits according to any one of claims 1 to 7.

10. A μLED light emission control method, characterized in that: The μLED light emission control method is performed by using the μLED unit circuit according to any one of claims 1 to 8, comprising a comparative light emission step, wherein the comparative light emission step comprises: Generate PWM signals with different pulse widths based on the light emitting control signal EM1 and a comparison reference signal SWEEP, wherein the comparison reference signal SWEEP is a linearly decreasing ramp signal; receiving the PWM signals of different pulse widths and controlling the on-time of the driving transistor based on the PWM signals of different pulse widths to provide a driving current; and The driving current is received from the light emission control circuit and the light emission time of the μLED is controlled based on the driving current.

11. The μLED light emission control method according to claim 10, characterized in that: The driving current is: Among them, the μ, C ox and represents the mobility, unit area gate dielectric capacitance and channel width-to-length ratio of the driving transistor respectively, PAMD is the voltage value when the luminous brightness is the highest, V LED is the voltage of the μLED, and V th10 is the threshold voltage of the driving transistor.

12. The μLED light emission control method according to claim 10, characterized in that: Before the comparative light emitting step, an initialization step and a row scanning step are also included. The initialization step initializes the μLED unit circuit of the pixel device based on a reset signal RESET; and The row scanning step, after the initialization step, scans the μLED unit circuit of the pixel device row by row based on the row scanning signal SN.

13. The μLED light emission control method according to claim 12, characterized in that: The initialization step includes: The reset signal RESET is provided to the gate of the first transistor T1, the first transistor T1 is turned on, so that the source of the first transistor T1 is connected to the reference power supply voltage REF to set the drain of the first transistor T1 to the reference power supply voltage REF, wherein the reset signal is at a low level.

14. The μLED light emission control method according to claim 13, characterized in that: The row scanning step comprises: The row scanning signal SN is provided to the gates of the second transistor T2 and the third transistor T3, and the second transistor T2, the third transistor T3, and the sixth transistor T6 are turned on, so that the source of the sixth transistor T6 is connected to the PWMD signal via the turned-on third transistor T3 and is set to PWMD, and the drain of the sixth transistor T6 is connected to the gate of the sixth transistor T6 via the second transistor T2, so that the drain voltage of the sixth transistor T6 and the gate voltage of the sixth transistor T6 are PWMD-|V th6 |, wherein the PWMD signal is a voltage value that changes according to the light luminance of the μLED; The row scan signal SN is provided to the gate of the ninth transistor T9, so that the ninth transistor T9 is turned on, so as to set the gate of the driving transistor to PAMD through the ninth transistor T9, wherein PAMD is the voltage value when the light brightness of the μLED is the highest, and the row scan signal SN is at a low level.

15. The μLED light emission control method according to claim 14, characterized in that: The step of comparing luminescence further comprises: The light emitting control signal EM1 is provided to the gates of the fourth transistor T4 and the fifth transistor T5, and the comparison reference signal SWEEP is provided to the gate of the sixth transistor T6 via the capacitor, the fourth transistor T4, the fifth transistor T5 and the sixth transistor T6 are turned on and connected as an inverter, so that the source of the sixth transistor T6 is the power input terminal of the inverter and is connected to the first power supply voltage VGL via the fourth transistor T4, so that the voltage of the power input terminal of the inverter is the first power supply voltage VGL; the gate of the sixth transistor T6 is the input terminal of the inverter and the voltage of the power input terminal of the inverter is PWMD+V th6 -ΔSWEEP; the drain of the sixth transistor T6 is the output end of the inverter and is connected to the reference power supply voltage REF via the fifth transistor T5, so that the voltage at the output end of the inverter is at a high level and the seventh transistor T7 remains cut off, wherein the size of the sixth transistor T6 is larger than the size of the fifth transistor T5, and the light emitting control signal EM1 is a pulse signal.

16. The μLED light emission control method according to claim 15, characterized in that: The step of comparing luminescence further comprises: The driving transistor T10 is turned on, so that the gate voltage of the driving transistor T10 maintains the PAMD signal, and the source of the driving transistor T10 is connected to the first power supply voltage VDD to provide the driving current, so that the μLED starts to emit light.

17. The μLED light emission control method according to claim 16, characterized in that: The step of comparing luminescence further comprises: When the comparison reference signal SWEEP increases linearly, the voltage PWMD+V th6 -ΔSWEEP is greater than VGH+V th6 When the sixth transistor T6 is turned off to raise the voltage of the output terminal of the inverter to REF, the seventh transistor T7 is turned on to transmit the first power supply voltage VDD to the gate of the driving transistor T10 or set the gate of the driving transistor T10 to the first power supply voltage VDD, and the driving transistor T10 is turned off so that the μLED stops emitting light.

18. The μLED light emission control method according to claim 15, characterized in that: The light-emitting control signal EM2 is provided to the eighth transistor T8, and the eighth transistor T8 and the driving transistor T10 are turned on, so that the gate voltage of the driving transistor T10 maintains the PAMD signal, and the source of the driving transistor T10 is connected to the first power supply voltage VDD to provide the driving current, so that the μLED starts to emit light, wherein the light-emitting control signal EM2 and the light-emitting control signal EM1 are pulse signals, and the rising edge of the light-emitting control signal EM2 lags behind the rising edge of the light-emitting control signal EM1.

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