Pixel driving circuit and driving method based on oxide semiconductor thin film transistor

Abstract

The invention discloses a pixel driving circuit and driving method based on an oxide semiconductor thin film transistor, the pixel driving circuit comprises a PWM module and a constant-current driving module connected with the PWM module, in the PWM module, a high-gain inverter is used for improving the circuit response speed, and in the constant-current driving module, the high-gain inverter is used for improving the circuit response speed. The current capacity of the circuit is improved by using the driving transistor made of a channel material with high carrier mobility, and meanwhile, the PWM module and the constant-current driving module both comprise threshold compensation circuits, so that the influence of device characteristic degradation on the circuit performance is reduced. According to the invention, through PWM modulation and threshold voltage compensation, the display brightness is controlled while the display color is ensured not to deviate, and the display quality is improved.

Description

Technical Field

[0001] The present invention belongs to the field of display technology, and in particular relates to a pixel driving circuit and a driving method based on an oxide semiconductor thin film transistor. Background Art

[0002] Micro-LED (μLED) has become a research hotspot for the next generation of display technology due to its outstanding features such as high brightness, high efficiency, high speed, high stability and high contrast. Pulse amplitude modulation (PAM) is usually used in traditional LED pixel driving circuits, in which grayscale is represented according to the driving current level. However, it is difficult to use PAM in μLED displays because the change in the driving current of μLED will cause the emission wavelength to shift and cause image distortion. To solve the above problems, μLED needs to use pulse width modulation (PWM) for pixel driving. PWM has high grayscale expression capabilities while avoiding the problem of wavelength shift.

[0003] Oxide semiconductor materials are ideal materials for making thin-film transistors (TFTs) for μLED pixel driving circuits due to their high carrier mobility, low preparation temperature, good electrical uniformity, transparency to visible light and low cost.

[0004] However, during the pixel driving process, the oxide semiconductor TFT will inevitably experience positive and negative gate voltage stress, which will cause its device characteristics, especially the threshold voltage, to shift, resulting in unsatisfactory display effects. Therefore, it is necessary to compensate for the degradation of device characteristics. In addition, due to the limited current driving capability and switching speed of TFT, it is necessary to use a switching circuit unit to improve the response speed, and use a channel material with high carrier mobility to improve the current capability of the circuit. Summary of the invention

[0005] Purpose of the invention: In order to solve the problems existing in the above-mentioned prior art, the present invention provides a pixel driving circuit and driving method based on oxide semiconductor thin film transistors.

[0006] Technical solution: The present invention provides a pixel driving circuit based on an oxide semiconductor thin film transistor, comprising a PWM module and a constant current driving module connected to the PWM module.

[0007] Furthermore, the PWM module includes a first transistor, a second transistor, a coupling capacitor and an inverter; the gate of the first transistor is connected to the first scan signal SCAN1, and the drain is connected to the first data signal V DATA1 , the source is connected to one end of the coupling capacitor, and the source of the first transistor is marked as point A, the gate of the second transistor is connected to the enable signal EM, and the drain is connected to the ramp signal V SWEEP, the source is connected to point A, the other end of the coupling capacitor is marked as point B, point B is connected to the input end of the inverter, the output end of the inverter is marked as point C, and the PWM signal is output to the constant current drive module.

[0008] Furthermore, the inverter includes third to fifth transistors, the gate of the third transistor is connected to the first scan signal SCAN1, the source is connected to point C, and the drain is connected to point B; the drain of the fourth transistor is connected to the power supply voltage VDD, and the gate and source are both connected to point C; the drain of the fifth transistor is connected to point C, the gate is connected to point B, and the source is grounded.

[0009] Further, the constant current driving module includes sixth to eleventh transistors, a light-emitting component and a storage capacitor; the drain of the sixth transistor is connected to one end of the light-emitting component, the gate is connected to the second scan signal SCAN2, the source is connected to the drain of the seventh transistor, and the drain of the eighth transistor; the other end of the light-emitting component is connected to the power supply voltage VDD; the gate of the seventh transistor is connected to the second scan signal SCAN3, the source is connected to the gate of the eighth transistor and one end of the storage capacitor, the other end of the storage capacitor is grounded, the source of the eighth transistor is connected to the source of the ninth transistor and the drain of the tenth transistor; the drain of the ninth transistor is connected to the second data signal V DATA2 , the gate is connected to the first scan signal SCAN1; the source of the tenth transistor is connected to the drain of the eleventh transistor, the gate is connected to the enable signal EM, the source of the eleventh transistor is grounded, and the gate is connected to the PWM module.

[0010] Furthermore, all transistors are N-type thin film transistors, which include a first oxide semiconductor and a second oxide semiconductor, and the mobility of the second oxide semiconductor is higher than that of the first oxide semiconductor.

[0011] Furthermore, the light emitting component adopts μLED, the drain of the sixth transistor is connected to the cathode of the μLED, and the anode of the μLED is connected to the power supply voltage VDD.

[0012] Furthermore, it is characterized in that:

[0013] In the initialization stage, the enable signal EM and the first scan signal SCAN1 are set to a low level, and the second scan signal SCAN2 and the third scan signal SCAN3 are set to a high level;

[0014] In the threshold compensation stage, the enable signal EM and the second scan signal SCAN2 are set to a low level, and the first scan signal SCAN1 and the third scan signal SCAN3 are set to a high level;

[0015] In the light-emitting stage, the enable signal EM and the second scan signal SCAN2 are set to a high level, and the first scan signal SCAN1 and the third scan signal SCAN3 are set to a low level. DATA1 The value of the signal adjusts the time when the PWM signal outputs a high level, thereby adjusting the light-emitting time of the light-emitting device; by adjusting V DATA2 The driving current is adjusted according to the value of , thereby ensuring that the display color does not shift while controlling the display brightness of the light-emitting device.

[0016] Beneficial effects: The present application reduces the fluctuation of the driving current through a threshold compensation circuit and adjusts the light-emitting time through a PWM module, thereby achieving control of the display brightness while ensuring that the display color does not shift, thereby improving the display quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 FIG. 4 is a schematic diagram of the overall circuit of this embodiment.

[0018] Figure 2 FIG. 4 is a driving timing diagram of the pixel driving circuit in this embodiment.

[0019] Figure 3 PWM signal waveform diagram of the pixel driving circuit of this embodiment.

[0020] Figure 4 is a driving current waveform diagram of the pixel driving circuit of this embodiment. DETAILED DESCRIPTION

[0021] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0022] The circuit diagram of the pixel driving circuit based on oxide semiconductor thin film transistor of this embodiment is as follows: Figure 1 As shown, the pixel driving circuit includes a PWM module 10 and a constant current 6T1C driving module 20 , and the PWM module 10 is electrically connected to the constant current 6T1C driving module 20 .

[0023] The PWM module 10 includes a first transistor T1 , a second transistor T2 , a coupling capacitor C1 and an inverter 100 .

[0024] The gate of the first transistor T1 receives a first scan signal SCAN1, the source of the first transistor T1 is connected to the first end of the coupling capacitor C1, and the drain of the first transistor T1 receives a first data signal V DATA1 , the first data signal V DATA1In the threshold compensation stage, the first end of the coupling capacitor C1 is written via the first transistor T1.

[0025] The gate of the second transistor T2 receives the enable signal EM, the source of the second transistor T2 is connected to the first end of the coupling capacitor C1, and the drain of the second transistor T2 receives the ramp signal V SWEEP , the ramp signal V SWEEP In the light emitting stage, the first end of the coupling capacitor C1 is written via the second transistor T2.

[0026] The first end of the inverter 100 is connected to the second end of the coupling capacitor C1 , and the second end of the inverter 100 is connected to the constant current 6T1C driving module 20 .

[0027] The first end of the coupling capacitor is recorded as a first circuit node A, and the second end of the coupling capacitor is recorded as a second circuit node B.

[0028] The first end of the inverter is recorded as a second circuit node B, and the second end of the inverter is recorded as a third circuit node C.

[0029] The inverter includes a third transistor T3, a fourth transistor T4, and a fifth transistor T5.

[0030] The gate of the third transistor T3 is used to receive the first scan signal SCAN1, the drain of the fourth transistor T4 receives the power supply voltage VDD, and the source of the fifth transistor is grounded (GND).

[0031] The drain of the third transistor T3 and the gate of the fifth transistor T5 are both connected to the second end of the coupling capacitor C1.

[0032] The source of the third transistor T3 , the gate of the fourth transistor T4 , the source of the fourth transistor T4 and the drain of the fifth transistor T5 are all connected to the constant current 6T1C driving module 20 .

[0033] The constant current 6T1C driving module 20 includes: a sixth transistor T6, a seventh transistor T7, a storage capacitor C2, an eighth transistor T8, a ninth transistor T9, a tenth transistor T10, and an eleventh transistor T11.

[0034] The gate of the sixth transistor T6 receives the second scan signal SCAN2 , and the drain of the sixth transistor T6 is connected to the cathode of the component to be illuminated. In this embodiment, the component to be illuminated is a μLED.

[0035] The gate of the seventh transistor T7 receives the third scan signal SCAN3 , the drain of the seventh transistor T7 , the source of the sixth transistor T6 and the drain of the eighth transistor T8 are connected, and the connection point is recorded as a node E.

[0036] The source of the seventh transistor T7 and the gate of the eighth transistor T8 are connected to the first end of the storage capacitor C2; the source of the eighth transistor T8 and the source of the ninth transistor T9 are connected to the drain of the tenth transistor T10. The source of the ninth transistor T9 is recorded as node F.

[0037] A second terminal of the storage capacitor C2 is connected to the ground GND.

[0038] The gate of the ninth transistor T9 receives the first scan signal SCAN1, and the drain of the ninth transistor T9 receives the second data signal V DATA2 , the second data signal V DATA2 The fifth circuit node F is written via the ninth transistor T9 during the threshold compensation phase.

[0039] A gate of the tenth transistor T10 receives an enable signal EM.

[0040] A gate of the eleventh transistor T11 is connected to the PWM module, and a source of the eleventh transistor T11 is grounded.

[0041] The first end of the storage capacitor C2 is recorded as a fourth circuit node D.

[0042] The transistors of the present application are all N-type thin film transistors, including a first oxide semiconductor (such as IGZO) TFT and a second oxide semiconductor (such as ITO) TFT, wherein the second oxide semiconductor TFT has a higher mobility than the first oxide semiconductor TFT to improve the current capacity of the circuit.

[0043] like Figure 2 As shown, the working cycle of the pixel driving circuit includes an initialization phase, a threshold compensation phase and a light emitting phase, and each working cycle can be used to drive and display one frame of picture.

[0044] In the initialization stage, the enable signal EM and the first scan signal SCAN1 are at a low level, the second scan signal SCAN2 and the third scan signal SCAN3 are at a high level, the power supply voltage charges the circuit node D to VDD via the sixth transistor T6 and the seventh transistor T7, the eighth transistor T8 is turned on, and the power supply voltage charges the circuit node F to VDD-V TH , where V TH is the threshold voltage of the eighth transistor T8.

[0045] In the threshold compensation stage, the enable signal EM and the second scan signal SCAN2 are at low levels, the first scan signal SCAN1 and the third scan signal SCAN3 are at high levels, and the first transistor T1 is turned on to charge the circuit node A to a preset V DATA1 The third transistor T3 is turned on, connecting the input and output nodes of the inverter 100, extracting the inverter flip voltage V T0 , at this time the voltage of node A is V DATA1 , the voltage at node B is V T0 , the voltage difference across the coupling capacitor C1 is V T0 -V DATA1 The seventh transistor T7 and the ninth transistor T9 are turned on, and the circuit node F is discharged to the preset V via the ninth transistor T9. DATA2 , the circuit node D is discharged to V via the seventh, eighth, and ninth transistors. DATA2 +V TH .

[0046] In the light-emitting stage, the enable signal EM is at a high level, the first scanning signal SCAN1 is at a low level, and the ramp signal V SWEEP Write to circuit node A, the voltage at circuit node B becomes V T0 -V DATA1 +V SWEEP , when V SWEEP Signal is less than V DATA1 signal, the voltage at point A is less than the inverter's flip voltage V T0 , so the PWM signal outputs a high level. When V SWEEP Signal greater than V DATA1 signal, the voltage at point A is greater than the inverter's flip voltage V T0 , so the PWM signal outputs a low level, by presetting different V DATA1 The value of the signal can adjust the time when the PWM signal outputs a high level, that is, to achieve the pulse width modulation function. Since the high and low level flip only depends on V DATA1 With V SWEEP The value of is independent of the inverter's flip voltage, so the generated PWM signal is not affected by device threshold degradation.

[0047] In the light-emitting stage, the enable signal EM and the second scan signal SCAN2 are at high levels, the first scan signal SCAN1 and the third scan signal SCAN3 are at low levels, and the voltage at point D remains at V DATA2 +V TH , the voltage at point F is discharged to 0V through the tenth and eleventh transistors, and the current flowing through the μLED depends on the eighth transistor T8. The current size can be expressed as:

[0048]

[0049] in is a constant related to process and drive design, such as μ n is the carrier mobility, C ox is the gate oxide capacitance, is the width-to-length ratio of the transistor. From the above formula, we can see that the driving current I is related to V TH has nothing to do with the V TH The drift of can improve the display quality of the display panel.

[0050] In this embodiment, V DATA1 The luminous time is adjusted by the preset V DATA2 The driving current is adjusted according to the value of , thereby controlling the display brightness while ensuring that the display color does not shift, thereby improving the display quality.

[0051] like Figure 3 As shown, setting different V DATA1 The value of , during the period when the enable signal EM is at a high level, a PWM signal with different duty cycles is obtained.

[0052] Depend on Figure 4 It can be seen that setting different threshold voltage offsets ΔV TH , the obtained driving current changes very little, and the threshold compensation plays an obvious role.

[0053] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

Claims

1. A pixel driving circuit based on an oxide semiconductor thin film transistor, characterized in that: It includes a PWM module and a constant current driving module connected with the PWM module.

2. The pixel driving circuit based on oxide semiconductor thin film transistor according to claim 1, characterized in that: The PWM module includes a first transistor, a second transistor, a coupling capacitor and an inverter; the gate of the first transistor is connected to the first scan signal SCAN1, and the drain is connected to the first data signal V DATA1 , the source is connected to one end of the coupling capacitor, and the source of the first transistor is marked as point A, the gate of the second transistor is connected to the enable signal EM, and the drain is connected to the ramp signal V SWEEP , the source is connected to point A, the other end of the coupling capacitor is marked as point B, point B is connected to the input end of the inverter, the output end of the inverter is marked as point C, and the PWM signal is output to the constant current drive module.

3. The pixel driving circuit based on oxide semiconductor thin film transistor according to claim 2, characterized in that: The inverter includes third to fifth transistors, the gate of the third transistor is connected to the first scan signal SCAN1, the source is connected to point C, and the drain is connected to point B; the drain of the fourth transistor is connected to the power supply voltage VDD, and the gate and source are both connected to point C; the drain of the fifth transistor is connected to point C, the gate is connected to point B, and the source is grounded.

4. The pixel driving circuit based on oxide semiconductor thin film transistor according to claim 2, characterized in that: The constant current driving module includes sixth to eleventh transistors, a light-emitting component and a storage capacitor; the drain of the sixth transistor is connected to one end of the light-emitting component, the gate is connected to the second scan signal SCAN2, the source is connected to the drain of the seventh transistor and the drain of the eighth transistor; the other end of the light-emitting component is connected to the power supply voltage VDD; the gate of the seventh transistor is connected to the second scan signal SCAN3, the source is connected to the gate of the eighth transistor and one end of the storage capacitor, the other end of the storage capacitor is grounded, the source of the eighth transistor is connected to the source of the ninth transistor and the drain of the tenth transistor; the drain of the ninth transistor is connected to the second data signal V DATA2 , the gate is connected to the first scan signal SCAN1; the source of the tenth transistor is connected to the drain of the eleventh transistor, the gate is connected to the enable signal EM, the source of the eleventh transistor is grounded, and the gate is connected to the PWM module.

5. The pixel driving circuit based on oxide semiconductor thin film transistor according to claim 4, characterized in that: All transistors are N-type thin film transistors, which include a first oxide semiconductor and a second oxide semiconductor, and the second oxide semiconductor has higher mobility than the first oxide semiconductor.

6. The pixel driving circuit based on oxide semiconductor thin film transistor according to claim 4, characterized in that: The light emitting component adopts μLED, the drain of the sixth transistor is connected to the cathode of the μLED, and the anode of the μLED is connected to the power supply voltage VDD.

7. The driving method of the pixel driving circuit based on the oxide semiconductor thin film transistor according to claim 4, characterized in that: Specifically: In the initialization stage, the enable signal EM and the first scan signal SCAN1 are set to a low level, and the second scan signal SCAN2 and the third scan signal SCAN3 are set to a high level; In the threshold compensation stage, the enable signal EM and the second scan signal SCAN2 are set to a low level, and the first scan signal SCAN1 and the third scan signal SCAN3 are set to a high level; In the light-emitting stage, the enable signal EM and the second scan signal SCAN2 are set to a high level, and the first scan signal SCAN1 and the third scan signal SCAN3 are set to a low level. DATA1 The value of the signal adjusts the time when the PWM signal outputs a high level, thereby adjusting the light-emitting time of the light-emitting device; by adjusting V DATA2 The driving current is adjusted according to the value of , thereby ensuring that the display color does not shift while controlling the display brightness of the light-emitting device.

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