A Micro-LED pixel driving circuit and driving method thereof

Abstract

The present invention discloses a Micro-LED pixel driving circuit and a driving method thereof, wherein the driving circuit comprises: a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a seventh transistor, an eighth transistor, a first capacitor, a second capacitor and a micro-light emitting diode; the present invention improves the display effect.

Description

Technical Field

[0001] The present invention relates to the field of display technology, and in particular to a Micro-LED pixel driving circuit and a driving method thereof. Background Art

[0002] Micro-LED display technology is a self-luminous display technology composed of an array of micron-scale semiconductor light-emitting units. It combines new display technology with light-emitting diode (LED) technology and has the advantages of high efficiency, low power consumption, high integration and high stability. Compared with traditional liquid crystal displays (LCD) and organic light-emitting diode (OLED) displays, Micro-LED can be applied to display screens of various sizes due to its small size, high flexibility, and easy disassembly and merging, and has more unique advantages in certain display effects. Micro-LED display technology is widely used in automotive displays, flexible displays, transparent displays, wearable devices, etc.

[0003] However, Micro-LED display technology faces many challenges in practical applications, among which the choice of driving mode is particularly critical. Micro-LED driving technology can be divided into passive matrix driving (PM) and active matrix driving (AM) according to different driving modes. The advantages of passive driving are relatively simple structure, low technical threshold and maturity, and low cost. However, since passive driving adopts a row-by-row scanning gating method, only one row of pixels is lit at the same time, while other rows of pixels are off, which will cause the average brightness of the display to decrease, especially when the number of rows increases, the brightness decrease is more obvious. To offset this problem, high voltage and high current are often required, but this will affect the luminous efficiency and service life of the device. In contrast, each pixel of the active driving method is equipped with an independent driving circuit, which is usually composed of multiple thin film transistors (TFT) or complementary metal oxide semiconductors (CMOS) and capacitors. By utilizing the storage characteristics of capacitors, active driving can avoid the use of large pulse driving voltage or current in passive driving, thereby improving the luminous efficiency and life of the device. However, traditional active driving circuits, such as 2T1C pixel driving circuits, are very sensitive to changes in the threshold voltage and mobility of transistors. As the working time goes by, these changes may cause the pixel light emission to be unstable, which in turn causes uneven light emission and inconsistent brightness between pixels, ultimately reducing the product yield. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a Micro-LED pixel driving circuit and a driving method thereof, which realizes a PWM driving mode, a threshold voltage and a VDD IR drop compensation, so as to solve the problems existing in the background technology.

[0005] Technical solution: A Micro-LED pixel driving circuit described in the present invention includes: a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a seventh transistor, an eighth transistor, a first capacitor, a second capacitor and a micro-light-emitting diode; wherein the gate of the first transistor is connected to one end of the first capacitor, namely, node A; the gate of the first transistor is respectively connected to the drain of the seventh transistor and the source of the second transistor through node A; the drain of the first transistor is connected to the source of the third transistor, and the source of the first transistor is connected to the power supply voltage; the gate of the second transistor is connected to the scan control signal, and the drain of the second transistor is connected to the source of the third transistor; the gate of the third transistor is connected to the enable control signal, and the drain of the third transistor is connected to the anode of the micro-light-emitting diode; the cathode of the micro-light-emitting diode is connected to a low voltage; the gate of the fourth transistor is connected to the initial voltage control signal, the source of the fourth transistor is connected to the initial voltage, and the drain of the fourth transistor is respectively connected to the drain of the fifth transistor and the drain of the sixth transistor through the other end of the first capacitor; the gate of the fifth transistor is connected to the reference voltage control signal, and the source of the fifth transistor is connected to the reference voltage; the gate of the sixth transistor is connected to the data voltage control signal, and the source of the sixth transistor is connected to the data voltage.

[0006] Furthermore, it also includes: the gate of the seventh transistor is connected to one end of the second capacitor, namely, node B, and the source of the seventh transistor is connected to the power supply voltage; the gate of the eighth transistor is connected to the PWM voltage control signal, the drain of the eighth transistor is connected to the gate of the seventh transistor through node B, and the source of the eighth transistor is connected to the PWM initialization voltage; one end of the second capacitor is connected to the scanning voltage.

[0007] Furthermore, the scanning control signal , Enable control signal , initial voltage control signal , reference voltage control signal , data voltage control signal , PWM voltage control signal and scanning voltage All are provided by external timing controller.

[0008] Furthermore, the driving timing of the Micro-LED pixel driving circuit includes: an initialization stage, a threshold voltage generation stage, a compensation stage and a light-emitting stage.

[0009] Further, the initialization stage is as follows: Scan control signal , Enable control signal , data voltage control signal , Scanning voltage Provides high potential, initial voltage control signal , reference voltage control signal , PWM voltage control signal Provides low potential.

[0010] Furthermore, the threshold voltage generation stage is as follows: the initial voltage control signal , Scan control signal , Enable control signal , data voltage control signal , Scanning voltage Provides high potential, reference voltage control signal , PWM voltage control signal Provides low potential.

[0011] Furthermore, the initial voltage control signal , reference voltage control signal , Scan control signal , Enable control signal , Scanning voltage Provide high potential, data voltage control signal , PWM voltage control signal Provides low potential.

[0012] Furthermore, the light-emitting stage is as follows: the initial voltage control signal , Scan control signal , reference voltage control signal , PWM voltage control signal Provide high potential to enable control signal , data voltage control signal Provide low potential, scan voltage It decreases linearly from high potential to low potential.

[0013] A driving method of a Micro-LED pixel driving circuit according to the present invention is based on the Micro-LED pixel driving circuit and comprises the following steps:

[0014] (1) Initialization phase, scanning control signal , Enable control signal , data voltage control signal , Scanning voltage Provides high potential, initial voltage control signal , reference voltage control signal , PWM voltage control signal Provide a low potential, the fourth transistor, the fifth transistor, and the eighth transistor are all turned on, and the first transistor, the second transistor, the third transistor, the sixth transistor, and the seventh transistor are all turned off. At this time, the voltage at node A is the initial voltage , the voltage at node B is the PWM initialization voltage , at this time the voltage difference between the two ends of the second capacitor is .

[0015] (2) Threshold voltage generation stage, initial voltage control signal , Scan control signal , Enable control signal , data voltage control signal , Scanning voltage Provides high potential, reference voltage control signal , PWM voltage control signal Provide a low potential, the second transistor, the fifth transistor, and the eighth transistor are all turned on, and the first transistor, the third transistor, the fourth transistor, the sixth transistor, and the seventh transistor are all turned off. At this time, the voltage value at node A is , so that the driving current has nothing to do with the threshold voltage of the driving tube. At this time, the voltage difference between the two ends of the first capacitor is ;

[0016] (3) Compensation stage, reference voltage control signal , Scan control signal , Enable control signal , Scanning voltage Provide high potential, data voltage control signal , PWM voltage control signal Provide a low potential. The sixth transistor and the eighth transistor are both turned on, and the first transistor, the second transistor, the third transistor, the fourth transistor, the fifth transistor, and the seventh transistor are all turned off. At this time, the voltage across the first capacitor remains unchanged, and the voltage at one end of the first capacitor is becomes , so the voltage at point A becomes , so that the subsequent driving current size has nothing to do with the power supply voltage;

[0017] (4) Light-emitting stage, initial voltage control signal , Scan control signal , reference voltage control signal , PWM voltage control signal Provide high potential to enable control signal , data voltage control signal Provide low potential, scan voltage The third transistor and the sixth transistor are turned on, the first transistor, the second transistor, the fourth transistor, the fifth transistor, the sixth transistor, and the eighth transistor are all turned off, and the seventh transistor is turned off. The voltage drops from closed to open. At this time, the voltage difference between the two ends of the second capacitor is ,along with When the voltage at point B decreases, When the seventh transistor is turned on, point A is connected to the power supply voltage , the first transistor T1 is turned off.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the present invention adopts a compensation circuit, generates a threshold voltage and a power supply voltage by connecting capacitor C1 and a transistor diode, and realizes a threshold voltage and VDD I-Rdrop compensation effect, so that the driving current is not affected by the driving tube threshold voltage and VDD IR drop, thereby improving the display effect, and realizes pulse width modulation of the pixel driving circuit by capacitor C2, and enables the Micro-LED to display different gray levels by controlling the width of the pulse. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a circuit diagram of a traditional 2T1C pixel driving circuit;

[0020] Figure 2 A circuit diagram of an 8T2C pixel driving circuit for Micro-LED driving according to the present invention;

[0021] Figure 3 This is a timing diagram of the 8T2C pixel driving circuit for Micro-LED driving of the present invention;

[0022] Figure 4 A schematic diagram of a circuit in the initialization phase of the pixel driving method of the present invention;

[0023] Figure 5 A circuit diagram of a threshold voltage generation stage in a pixel driving method of the present invention;

[0024] Figure 6 is a circuit diagram of the compensation stage in the pixel driving method of the present invention;

[0025] Figure 7 It is a circuit diagram of the light emitting stage in the pixel driving method of the present invention. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0027] like Figure 1As shown in the figure, the traditional 2T1C pixel driving circuit is very sensitive to changes in the threshold voltage and mobility of the transistor. As the working time goes by, these changes may cause unstable pixel light emission, which in turn causes uneven light emission and inconsistent brightness between pixels, ultimately reducing the product yield. The 2T1C pixel driving circuit uses pulse amplitude modulation, which is inefficient when driving Micro-LEDs with small currents, and is not conducive to Micro-LEDs displaying different grayscales.

[0028] The embodiment of the present invention provides a pixel driving circuit of a Micro-LED, such as Figure 2 to Figure 7 As shown, it includes: a first transistor T1, a second transistor T2, a third transistor T3, a fourth transistor T4, a fifth transistor T5, a sixth transistor T6, a seventh transistor T7 and an eighth transistor T8, a first capacitor C1, a second capacitor C2 and a micro light emitting diode Micro-LED.

[0029] The specific connection mode is as follows: the gate of the first transistor T1 is connected to one end of the first capacitor C1, namely, the node A; the gate of the first transistor T1 is respectively connected to the drain of the seventh transistor T7 and the source of the second transistor T2 through the node A; the drain of the first transistor T1 is connected to the source of the third transistor T3, and the source of the first transistor T1 is connected to the power supply voltage; the gate of the second transistor T2 is connected to the scan control signal, and the drain of the second transistor T2 is connected to the source of the third transistor T3; the gate of the third transistor T3 is connected to the enable control signal, and the drain of the third transistor T3 is connected to the anode of the micro-light emitting diode Micro-LED; the cathode of the micro-light emitting diode Micro-LED is connected to the low voltage; the gate of the fourth transistor T4 is connected to the initial voltage control signal, the source of the fourth transistor T4 is connected to the initial voltage, and the drain of the fourth transistor T4 is respectively connected to the drain of the fifth transistor T5 and the drain of the sixth transistor T6 through the other end of the first capacitor C1; the gate of the fifth transistor T5 is connected to the reference voltage control signal, and the source of the fifth transistor T5 is connected to the reference voltage; the gate of the sixth transistor T6 is connected to the data voltage control signal, and the source of the sixth transistor T6 is connected to the data voltage. The gate of the seventh transistor T7 is connected to one end of the second capacitor C2, i.e., node B, and the source of the seventh transistor T7 is connected to the power supply voltage; the gate of the eighth transistor T8 is connected to the PWM voltage control signal, the drain of the eighth transistor T8 is connected to the gate of the seventh transistor T7 through node B, and the source of the eighth transistor T8 is connected to the PWM initialization voltage; one end of the second capacitor C2 is connected to the scan voltage;

[0030] The transistor of the Micro-LED driving circuit can be a thin film transistor (TFT) or a silicon-based complementary metal oxide semiconductor (silicon-based CMOS). Scanning control signal , Enable control signal , initial voltage control signal , reference voltage control signal , data voltage control signal , PWM control signal , and scanning voltage All are provided by external timing controller.

[0031] like Figure 3 As shown, the scan control signal , Enable control signal , initial voltage control signal , reference voltage control signal , data voltage control signal , PWM control signal and scanning voltage After combination, it corresponds to the initialization stage, the threshold voltage generation stage, the compensation stage, and the light emitting stage.

[0032] The embodiment of the present invention further provides a driving method of a Micro-LED pixel driving circuit, comprising the following steps: Figure 2 The 8T2C Micro-LED pixel driver circuit is shown in the initialization stage. Figure 3 and Figure 4 , scan control signal , Enable control signal , data voltage control signal , Scanning voltage Provides high potential, initial voltage control signal , reference voltage control signal , PWM voltage control signal Provide a low potential, the fourth transistor T4, the fifth transistor T5, and the eighth transistor T8 are all turned on, the first transistor T1, the second transistor T2, the third transistor T3, the sixth transistor T6, and the seventh transistor T7 are all turned off, and the voltage at the node A is the initial voltage , the voltage at node B is the PWM initialization voltage , at this time the voltage difference between the two ends of the second capacitor C2 is .

[0033] Entering the threshold voltage generation stage, the initial voltage control signal , Scan control signal , Enable control signal , data voltage control signal , Scanning voltage Provides high potential, reference voltage control signal , PWM voltage control signal Provide a low potential, the second transistor T2, the fifth transistor T5, and the eighth transistor T8 are all turned on, the first transistor T1, the third transistor T3, the fourth transistor T4, the sixth transistor T6, and the seventh transistor T7 are all turned off, and the voltage value at the node A is , so that the driving current has nothing to do with the threshold voltage of the driving tube. At this time, the voltage difference between the two ends of the first capacitor C1 is .

[0034] Entering the compensation phase, the reference voltage control signal , Scan control signal , Enable control signal , Scanning voltage Provide high potential, data voltage control signal , PWM voltage control signal Provide a low potential. The sixth transistor T6 and the eighth transistor T8 are both turned on, and the first transistor T1, the second transistor T2, the third transistor T3, the fourth transistor T4, the fifth transistor T5, and the seventh transistor T7 are all turned off. At this time, the voltage across the first capacitor C1 remains unchanged, and the voltage at one end of the first capacitor C1 is becomes , so the voltage at point A becomes , making the subsequent driving current independent of the power supply voltage.

[0035] Entering the light-emitting stage, the initial voltage control signal , Scan control signal , reference voltage control signal , PWM voltage control signal Provide high potential to enable control signal , data voltage control signal Provide low potential, scan voltage The third transistor T3 and the sixth transistor T6 are turned on, and the first transistor T1, the second transistor T2, the fourth transistor T4, the fifth transistor T5, the sixth transistor T3, and the eighth transistor T8 are all turned off. At this time, the driving current formula is:

[0036] ;

[0037] ;

[0038] ;

[0039] in, is the driving current of the Micro-LED pixel circuit, is the carrier mobility, is the gate oxide layer capacitance, W and L are the width and length of the driver tube, is the power supply voltage, is the reference voltage, is the data voltage, is the driver threshold voltage.

[0040] It can be seen that the size of the drive current is only related to the driver tube mobility, gate capacitance, device size, and reference voltage. And data voltage related to the threshold voltage and supply voltage The seventh transistor T7 is independent of the threshold voltage and VDD IR drop compensation. The voltage drops from closed to open. At this time, the voltage at point B is affected by the second capacitor C2. ,along with Drop, voltage Also decreases when When the seventh transistor T7 is turned on, point A is connected to the power supply voltage ,at this time , the first transistor T1 is turned off, the light-emitting phase ends, and the control and The relationship between the two can control the duty cycle of PWM, thereby controlling the Micro-LED to display different grayscales.

Claims

1. A Micro-LED pixel driving circuit, characterized in that: include: A first transistor (T1), a second transistor (T2), a third transistor (T3), a fourth transistor (T4), a fifth transistor (T5), a sixth transistor (T6), a seventh transistor (T7), an eighth transistor (T8), a first capacitor (C1), a second capacitor (C2) and a micro-light emitting diode (Micro-LED); wherein the gate of the first transistor (T1) is connected to one end of the first capacitor (C1), i.e., node A; the gate of the first transistor (T1) is connected to the drain of the seventh transistor (T7) and the source of the second transistor (T2) through node A; the drain of the first transistor (T1) is connected to the source of the third transistor (T3), and the source of the first transistor (T1) is connected to a power supply voltage; the gate of the second transistor (T2) is connected to a scan control signal, and the drain of the second transistor (T2) is connected to the source of the third transistor (T3); The gate of the third transistor (T3) is connected to the enable control signal, the drain of the third transistor (T3) is connected to the anode of the micro-light emitting diode (Micro-LED); the cathode of the micro-light emitting diode (Micro-LED) is connected to the low voltage; the gate of the fourth transistor (T4) is connected to the initial voltage control signal, the source of the fourth transistor (T4) is connected to the initial voltage, and the drain of the fourth transistor (T4) is respectively connected to the drain of the fifth transistor (T5) and the drain of the sixth transistor (T6) through the other end of the first capacitor (C1); the gate of the fifth transistor (T5) is connected to the reference voltage control signal, and the source of the fourth transistor (T4) is connected to the initial voltage. The source of the transistor (T5) is connected to a reference voltage; the gate of the sixth transistor (T6) is connected to a data voltage control signal, and the source of the sixth transistor (T6) is connected to the data voltage; the gate of the seventh transistor (T7) is connected to one end of the second capacitor (C2), i.e., node B, and the source of the seventh transistor (T7) is connected to a power supply voltage; the gate of the eighth transistor (T8) is connected to a PWM voltage control signal, the drain of the eighth transistor (T8) is connected to the gate of the seventh transistor (T7) through node B, and the source of the eighth transistor (T8) is connected to a PWM initialization voltage; and one end of the second capacitor (C2) is connected to a scan voltage.

2. A Micro-LED pixel driving circuit according to claim 1, characterized in that: Scan control signal , Enable control signal , initial voltage control signal , reference voltage control signal , data voltage control signal , PWM voltage control signal and scanning voltage All are provided by external timing controller.

3. The Micro-LED pixel driving circuit according to claim 1, characterized in that: The driving timing of the Micro-LED pixel driving circuit includes: initialization stage, threshold voltage generation stage, compensation stage and light-emitting stage.

4. A Micro-LED pixel driving circuit according to claim 3, characterized in that: The initialization phase is as follows: Scan control signal , Enable control signal , data voltage control signal , Scanning voltage Provides high potential, initial voltage control signal , reference voltage control signal , PWM voltage control signal Provides low potential.

5. The Micro-LED pixel driving circuit according to claim 3, characterized in that: The threshold voltage generation stage is as follows: the initial voltage control signal , Scan control signal , Enable control signal , data voltage control signal , Scanning voltage Provides high potential, reference voltage control signal , PWM voltage control signal Provides low potential.

6. The Micro-LED pixel driving circuit according to claim 3, characterized in that: The compensation stage is as follows: The initial voltage control signal , reference voltage control signal , Scan control signal , Enable control signal , Scanning voltage Provide high potential, data voltage control signal , PWM voltage control signal Provides low potential.

7. The Micro-LED pixel driving circuit according to claim 3, characterized in that: The specific lighting stage is as follows: initial voltage control signal , Scan control signal , reference voltage control signal , PWM voltage control signal Provide high potential to enable control signal , data voltage control signal Provide low potential, scan voltage It decreases linearly from high potential to low potential.

8. A driving method of the Micro-LED pixel driving circuit according to claim 1, characterized in that: Based on Micro-LED pixel driving circuit, including the following steps: (1) Initialization phase: scanning control signal , Enable control signal , data voltage control signal , Scanning voltage Provides high potential, initial voltage control signal , reference voltage control signal , PWM voltage control signal Provide a low potential, the fourth transistor (T4), the fifth transistor (T5), and the eighth transistor (T8) are all turned on, the first transistor (T1), the second transistor (T2), the third transistor (T3), the sixth transistor (T6), and the seventh transistor (T7) are all turned off, and the voltage value at node A is the initial voltage , the voltage at node B is the PWM initialization voltage , at this time the voltage difference between the two ends of the second capacitor (C2) is ; (2) Threshold voltage generation stage: initial voltage control signal , Scan control signal , Enable control signal , data voltage control signal , Scanning voltage Provides high potential, reference voltage control signal , PWM voltage control signal Provide a low potential, the second transistor (T2), the fifth transistor (T5), and the eighth transistor (T8) are all turned on, the first transistor (T1), the third transistor (T3), the fourth transistor (T4), the sixth transistor (T6), and the seventh transistor (T7) are all turned off, and the voltage value at node A is , so that the driving current has nothing to do with the threshold voltage of the driving tube. At this time, the voltage difference between the two ends of the first capacitor (C1) is ; (3) Compensation stage: reference voltage control signal , Scan control signal , Enable control signal , Scanning voltage Provide high potential, data voltage control signal , PWM voltage control signal Provide a low potential; the sixth transistor (T6) and the eighth transistor (T8) are turned on, and the first transistor (T1), the second transistor (T2), the third transistor (T3), the fourth transistor (T4), the fifth transistor (T5), and the seventh transistor (T7) are turned off; at this time, the voltage across the first capacitor (C1) remains unchanged, and the voltage at one end of the first capacitor (C1) is becomes , so the voltage at point A becomes , so that the subsequent driving current size has nothing to do with the power supply voltage; (4) Light-emitting stage: initial voltage control signal , Scan control signal , reference voltage control signal , PWM voltage control signal Provide high potential to enable control signal , data voltage control signal Provide low potential, scan voltage The potential decreases linearly from a high potential to a low potential; the third transistor (T3) and the sixth transistor (T6) are turned on, the first transistor (T1), the second transistor (T2), the fourth transistor (T4), the fifth transistor (T5), the sixth transistor (T3), and the eighth transistor (T8) are all turned off, and the seventh transistor (T7) is turned on as The voltage drops from closed to open; at this time, the voltage difference across the second capacitor (C2) is ,along with When the voltage at point B decreases, When the seventh transistor (T7) is turned on, point A is connected to the power supply voltage , the first transistor (T1) is turned off.

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