Novel electro-optical device and driving method

Abstract

The invention provides a high-resolution and consistent micro-oled pixel driving circuit and method, and the circuit is characterized in that a signal line with a reset switch transmits step initialization voltage and data voltage to a relay line through a transmission capacitor (CS1), and the relay line is connected with the input end of a whole column of pixel circuits at the same time. The pixel circuit includes: a light emitting element; an N-type driving transistor that causes the light-emitting element to emit light; a first switching tube (WS) for controlling data voltage writing; the second switch tube (AZ2) controls the driving tube to work in a saturation region; the third switch tube (DS) is connected with the drain electrode of the driving tube and the power supply; a fourth switching tube (AZ1) for discharging the anode of the light-emitting element; and the storage capacitor stores the threshold voltage and the data voltage. The pixel circuit is matched with a control signal of a driving circuit, the non-uniform threshold voltage of a transistor and the degradation of the voltage of a storage capacitor can be effectively compensated, so that the brightness of an OLED display picture is uniform, and high contrast is realized.

Description

Technical Field

[0001] This invention relates to the field of display technology, and more specifically, to a pixel driving circuit and method. Background Technology

[0002] With the continuous development of display technology and semiconductor processes, Organic Light-Emitting Diodes (OLEDs) have been widely used in display fields such as mobile phones, home appliances, and automobiles due to their characteristics of self-illumination, wide viewing angle, fast display, fast response, and ability to be fabricated on flexible substrates. Currently, OLEDs typically employ active matrix driving, configured as follows: pixel circuits, composed of light-emitting elements and their driving circuits, are located at each intersection of multiple horizontal scan lines and multiple vertical data lines (signal lines) on the display panel. These pixel circuits are arranged along both the horizontal and vertical directions. Each pixel has a storage capacitor used to store the data voltage applied to the gate of the driving transistor according to the pixel's grayscale. Therefore, the driving transistor can also provide current to the light-emitting element based on the gate-source voltage during the data writing phase, and the light-emitting element emits light with brightness according to the grayscale level.

[0003] However, slight differences in the threshold voltage (hereinafter referred to as Vth) of the driving transistors between different pixel circuits in the display panel due to process variations, or drift of the threshold voltage of the driving transistors in the pixel circuit over time, can cause differences in the current of the OLED light-emitting elements in each pixel circuit. This results in poor uniformity of display brightness and degraded image quality. To prevent image quality degradation, it is necessary to compensate for changes in Vth.

[0004] A traditional Vth compensation method couples the gate and drain of the driving transistor to the data signal supply line, disconnects it after the initial voltage is applied, and the driving transistor remains in diode connection mode. Its gate voltage decays to Vth and is held by the storage capacitor until the data writing phase. However, due to parasitic capacitance on the data signal supply line, these parasitic capacitances are simultaneously charged or discharged during the compensation operation, which prolongs the compensation cycle. If the time required to charge or discharge the parasitic capacitors is not considered, the compensation may become insufficient. Patent Document 1 provides a circuit structure with a "relay line" that replaces the signal supply line, coupling multiple pixels vertically and holding charge during Vth correction for each pixel, thereby achieving high-speed driving.

[0005] However, the configuration in Patent Document 1 requires five MOSFETs (of which the driving transistors are P-type) and one capacitor as components to form a pixel circuit, which places a high demand on the number of components, making high-definition layout difficult. At the same time, P-type transistors have a narrow data voltage input range and are accompanied by severe IR drop; in contrast, while N-type transistors have a wide data voltage input range, their drains are usually connected to the power supply, making them incompatible with existing pixel circuit structures with compensation functions.

[0006] The purpose of this technology is to provide an electro-optic device and driving method that not only accelerates threshold compensation operation, but also achieves better consistency and a wider input data voltage range by using NMOS as the driving transistor. Pixels in the same row can share a single switch (DS) that connects the power supply and the gate of the driving transistor. Therefore, an external row driver can be used to replace its function, compensating for the threshold voltage variation of the transistor with fewer components and avoiding high power consumption.

[0007] Patent documents Patent Document 1: CN 112567448 A Summary of the Invention

[0008] A novel electro-optic device and driving method are achieved through the following technical solution: A novel electro-optical device includes: a signal line; a relay line; a scan line; a power supply line providing a path for current discharge; a transmission capacitor coupled between the signal line and the relay line; a pixel circuit disposed corresponding to the relay line and the scan line; and a driving circuit for driving the pixel circuit. The pixel circuit includes: First transistor (WS), second transistor (AZ2), third transistor (DS), fourth transistor (AZ1), driving transistor, storage capacitor (CS2), OLED; The drain of the driving transistor is connected to the source of the second transistor and the drain of the third transistor, the gate is connected to the drain of the first transistor and terminal A of the storage capacitor, and the source is connected to the source of the fourth transistor and the anode of the light-emitting diode. The driving transistor is used to drive the OLED to emit light, and terminal B of the storage capacitor is connected to the power supply line AVSS. The drain of the first transistor is connected to the gate of the driving transistor and the A terminal of the storage capacitor. The gate is connected to the first scan control line S1, and the source is connected to the drain of the fourth transistor and the relay line. The first transistor acts as a switch to transmit the initial voltage and data level to the gate of the driving transistor during the initialization phase and the data writing phase, respectively. The drain of the second transistor is connected to the source of the first transistor and the relay line, the gate is connected to the second scan control line S2, and the source is connected to the source of the third transistor and the drain of the driving transistor. When the second transistor is turned on, the driving transistor is connected in a diode configuration, so that the circuit can generate the threshold voltage of the first transistor itself during the compensation phase and record it. The drain of the third transistor is connected to the drain of the driving transistor and the source of the second transistor. The gate is connected to the third scan control line S3, and the source is connected to the power supply. The third transistor is not fully turned on during the initialization phase, and controls the current from the power supply through the driving transistor to the power supply line (AVSS) and initializes the gate voltage of the driving transistor. It is fully turned on during the light emission phase. The drain of the fourth transistor is connected to the source of the driving transistor and the anode of the OLED, the gate is connected to the fourth scan control line S4, and the source is connected to the power supply line. The fourth transistor is used to discharge the current of the OLED anode.

[0009] The driving method for the pixel circuit of the novel electro-optic device described above includes the following steps: (1) Initialization phase: The driving circuit turns on the first transistor, the second transistor and the fourth transistor in the pixel circuit. The third transistor is not fully turned on in this phase, and the initial voltage of the power supply is written into the gate of the driving transistor through the first transistor, the second transistor and the third transistor. (2) Compensation stage: The driving circuit cuts off the third transistor in the corresponding pixel circuit to correct the threshold voltage of the driving transistor, which is recorded by the storage capacitor; (3) Data writing stage: When the driving circuit turns on the first transistor and the fourth transistor in the corresponding pixel circuit, the data voltage is written to the storage capacitor in the form of a step signal through the transmission capacitor. At this time, the gate voltage of the driving transistor is theoretically the sum of the threshold voltage of the driving transistor and the data voltage. (4) During the light-emitting stage, the driving circuit turns on the third transistor in the corresponding pixel circuit, and the power supply generates a corresponding current through the corresponding third transistor and the driving transistor according to the storage capacitor voltage and enters the OLED. Attached Figure Description

[0010] The subject matter of this invention is specifically pointed out in the claims of this patent application, and patent protection is clearly sought therein. A better understanding of the relevant structure and implementation method of the invention, as well as its objects, features, and advantages, can be obtained by referring to the following detailed description and accompanying drawings. Although not shown, the electro-optical device includes a display panel and control circuitry for controlling the operation of the display panel. The display panel includes a plurality of pixel circuits and driving circuitry for driving the pixel circuits. The plurality of pixel circuits and driving circuitry included in the display panel are formed on a silicon substrate, and organic light-emitting diodes (OLEDs) are used as an example of light-emitting elements in the pixel circuits.

[0011] Figure 1 It is a new type of pixel circuit and driving circuit for an electro-optical device.

[0012] Figure 2 yes Figure 1 The signal timing diagram. Detailed Implementation

[0013] In the following detailed description, specific details are set forth in order to provide a full understanding of the invention. However, those skilled in the art will recognize that the invention may also be practiced with other similar details. Example

[0014] like Figure 1 As shown, the present invention discloses a novel electro-optic device and driving method. The pixel circuit includes a driving transistor, a first transistor WS, a second transistor AZ2, a third transistor DS, a fourth transistor AZ1, a storage capacitor CS2, and a light-emitting diode OLED. The driving circuit includes a signal line Vsig, a transmission gate, a reset transistor OFS, a transmission capacitor CS1, a first scan line S1, a second scan line S2, a third scan line S3, a fourth scan line S4, a power supply line AVDD, a power supply line AVSS, and a relay line.

[0015] The drain of the driving transistor is connected to the source of the second transistor AZ2 and the drain of the third transistor DS. The gate is connected to the drain of the first transistor WS and the A terminal of the storage capacitor CS2. The source is connected to the source of the fourth transistor AZ1 and the anode of the light-emitting diode OLED. The driving transistor is used to drive the OLED to emit light. The B terminal of the storage capacitor CS2 is connected to the power supply line AVSS. The drain of the first transistor WS is connected to the gate of the driving transistor and the A terminal of the storage capacitor CS2. The gate is connected to the first scan control line S1, and the source is connected to the drain of the fourth transistor AZ1 and the relay line. The first transistor WS acts as a switch to transmit the initial voltage and data level to the gate of the driving transistor during the initialization phase and the data writing phase, respectively. The drain of the second transistor AZ2 is connected to the source of the first transistor WS and the relay line, the gate is connected to the second scan control line, and the source is connected to the source of the third transistor DS and the drain of the driving transistor. When the second transistor AZ2 is turned on, the driving transistor is connected in a diode configuration, so that its gate voltage can be attenuated to the threshold voltage of the driving transistor itself during the compensation phase and recorded by the storage capacitor CS2. The drain of the third transistor DS is connected to the drain of the driving transistor and the source of the second transistor AZ2. The gate is connected to the third scan control line S3, and the source is connected to the power supply. The third transistor DS is not fully turned on during the initialization phase, and controls the current from the power supply through the driving transistor to the power supply line AVSS and initializes the gate voltage of the driving transistor. It is fully turned on during the light emission phase. The drain of the fourth transistor AZ1 is connected to the source of the driving transistor and the anode of the OLED, the gate is connected to the fourth scan control line S4, and the source is connected to the power supply line. The fourth transistor AZ1 is used to discharge the current of the OLED anode.

[0016] The pixel driving circuit is implemented through the following steps: (1) Initialization stage: The first scan control line S1, the second scan control line S2 and the fourth scan control line S4 are at high level, the third scan control line S3 is close to high level, the first transistor WS, the second transistor AZ2 and the fourth transistor AZ1 are turned on, the third transistor DS is not fully turned on in this stage, and the initial voltage of the power supply is written to the gate of the driving transistor through the first transistor WS, the second transistor AZ2 and the third transistor DS. (2) Compensation Stage: The first scan control line S1, the second scan control line S2, the third scan control line S3, and the fourth scan control line S4 are all at a high level. The first transistor WS, the second transistor AZ2, and the fourth transistor AZ1 are turned on, while the third transistor DS is turned off during this stage. The gate voltage of the driving transistor naturally decays from the initial voltage to its threshold voltage Vth, which is recorded by the storage capacitor CS2. During this stage, the transistor OFS is turned on and the transmission gate is turned off. At this time, the relay line is short-circuited, so the time required for charging or discharging the parasitic capacitance of the relay line is shortened, and the Vth compensation time is shortened. (3) Data writing stage: The first scan control line S1, the third scan control line S3 and the fourth scan control line S4 are all at high level, the second scan control line S2 is at low level, the first transistor WS and the fourth transistor AZ1 are turned on, the second transistor AZ2 and the third transistor DS are turned off in this stage, and the data voltage Vdata is written to the storage capacitor CS2 in the form of a step signal through the transmission capacitor CS1. At this time, the gate voltage of the driving transistor is theoretically the sum of the driving transistor threshold voltage Vth and the step data voltage Vdata × CS1 / (CS1 + CS2) after voltage division by the capacitor. (4) Light emission stage: The first scan control line S1, the second scan control line S2, the third scan control line S3 and the fourth scan control line S4 are all at low level. The third transistor DS is turned on. The first transistor WS, the second transistor AZ2 and the fourth transistor AZ1 are turned off in this stage. At this time, the gate-source voltage of the driving transistor VGS = Vth + VDATA × CS1 / (CS1 + CS2) and the current formula of the driving transistor is Id = K(VGS - VTH)^2, where K is a fixed process parameter. Substituting VGS into the current formula, we can get Id = K(VDATA × CS1 / (CS1 + CS2))^2. From the current formula, we can see that the current flowing through the light-emitting diode OLED is independent of the threshold voltage Vth of the driving transistor.

[0017] While certain features and one implementation of the invention have been described herein, many modifications, substitutions, variations, and equivalents will be apparent to those skilled in the art. Therefore, the scope of protection of this invention is determined by the appended claims.

Claims

1. An electro-optical device, comprising: signal line; Repeater; Scan lines; Power supply lines provide a path for current discharge; A transmission capacitor is coupled between the signal line and the relay line; Pixel circuits are provided corresponding to the relay lines and the scan lines; A driving circuit drives the pixel circuit. The pixel circuit includes: First transistor (WS), second transistor (AZ2), third transistor (DS), fourth transistor (AZ1), driving transistor, storage capacitor (CS2), OLED; The drain of the driving transistor is connected to the source of the second transistor and the drain of the third transistor, the gate is connected to the drain of the first transistor and terminal A of the storage capacitor, and the source is connected to the source of the fourth transistor and the anode of the light-emitting diode. The driving transistor is used to drive the OLED to emit light, and terminal B of the storage capacitor is connected to the power supply line AVSS. The drain of the first transistor is connected to the gate of the driving transistor and the A terminal of the storage capacitor. The gate is connected to the first scan control line S1, and the source is connected to the drain of the fourth transistor and the relay line. The first transistor acts as a switch to transmit the initial voltage and data level to the gate of the driving transistor during the initialization phase and the data writing phase, respectively. The drain of the second transistor is connected to the source of the first transistor and the relay line, the gate is connected to the second scan control line S2, and the source is connected to the source of the third transistor and the drain of the driving transistor. When the second transistor is turned on, the driving transistor is connected in a diode configuration, so that the circuit can generate the threshold voltage of the first transistor itself during the compensation phase and record it. The drain of the third transistor is connected to the drain of the driving transistor and the source of the second transistor. The gate is connected to the third scan control line S3, and the source is connected to the power supply. The third transistor is not fully turned on during the initialization phase, and controls the current from the power supply through the driving transistor to the power supply line (AVSS) and initializes the gate voltage of the driving transistor. It is fully turned on during the light emission phase. The drain of the fourth transistor is connected to the source of the driving transistor and the anode of the OLED, the gate is connected to the fourth scan control line S4, and the source is connected to the power supply line. The fourth transistor is used to discharge the current of the OLED anode.

2. The electro-optical device according to claim 1, characterized in that, The transistors described above are complementary metal-oxide-semiconductor (CMOS) transistors; the light-emitting element is a micro-OLED.

3. The driving circuit according to claim 1, characterized in that... Includes the following steps: (1) Initialization phase: The driving circuit turns on the first transistor, the second transistor and the fourth transistor in the pixel circuit. The third transistor is not fully turned on in this phase, and the initial voltage of the power supply is written into the gate of the driving transistor through the first transistor, the second transistor and the third transistor. (2) Compensation stage: The driving circuit cuts off the third transistor in the corresponding pixel circuit to correct the threshold voltage of the driving transistor, which is recorded by the storage capacitor; (3) Data writing stage: When the driving circuit turns on the first transistor and the fourth transistor in the corresponding pixel circuit, the data voltage is written to the storage capacitor in the form of a step signal through the transmission capacitor. At this time, the gate voltage of the driving transistor is theoretically the sum of the threshold voltage of the driving transistor and the data voltage. (4) Light emission stage: The driving circuit turns on the third transistor in the corresponding pixel circuit, and the power supply enters the OLED through the corresponding third transistor and the driving transistor according to the storage capacitor voltage.

4. The pixel circuit according to claim 1, characterized in that, The third transistor is a PMOS. The level of the third scan control line in step (1) should not be too high or too low (e.g., 4.35V). The third transistor should be operated in the linear region so that the gate voltage of the driving transistor can be initialized normally to complete the threshold correction. The current from the power supply through the third transistor, the driving transistor and the fourth transistor to the power supply line should be low enough to have a small impact on the total power consumption.

5. The pixel circuit according to claim 1, characterized in that, The level used to provide a current discharge path is set such that the fourth transistor is turned on in steps (1) and (2), while the light-emitting element is quenched.

6. The pixel circuit according to claim 1, characterized in that, The storage capacitor and the transmission capacitor are metal-insulator-metal type capacitors, wherein the storage capacitor and the transmission capacitor are multilayer capacitors.

7. The pixel circuit according to claim 1, characterized in that, To further save pixel circuit area, the third transistor can be placed outside the pixel circuit, and the conduction timing of the driving transistor is controlled by an external row drive power supply, with its function and requirements being consistent with those described in step (1).

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