Pixel circuit, driving method thereof, display device and display panel thereof

Abstract

The application discloses a pixel circuit and a driving method thereof, and a display device and a display panel thereof. The pixel circuit comprises a first thin film transistor for transmitting a data voltage; a second thin film transistor connected with the first thin film transistor at a node for providing a driving current; a light emitting element for emitting light under the driving of the driving current; and a compensation module connected between a first power voltage and a ground and connected with the node, for storing a threshold voltage of the second thin film transistor at the node in a threshold voltage acquisition stage, superimposing the threshold voltage and a voltage related to the data voltage as a driving voltage and storing the driving voltage at the node in a gray scale voltage writing stage, and providing the driving voltage to the second thin film transistor to make it generate the driving current in a light emitting stage. The first power voltage is in a high resistance state in the threshold voltage acquisition stage and the gray scale voltage writing stage, which not only can solve the problem of uneven display brightness of the display panel caused by manufacturing process, but also can reduce power consumption.

Description

Technical Field

[0001] This invention relates to the field of display technology, and in particular to a pixel circuit and its driving method, as well as a display device and its display panel. Background Technology

[0002] OLED (Organic Light-Emitting Diode) is an emerging flat panel display device. Due to its advantages such as self-illumination, high contrast, and wide color gamut, as well as its simple manufacturing process, low cost, low power consumption, and ease of realizing flexible displays, it has broad application prospects.

[0003] In existing technologies, the luminous intensity of an organic light-emitting diode (OLED) is determined by the data voltage VDATA, the power supply voltage VDD, and the threshold voltage Vth of the driving transistor that drives the OLED. Due to manufacturing process factors, the threshold voltage Vth of the driving transistors fabricated on a large-area glass substrate varies, resulting in differences in brightness between adjacent pixel circuits even when the same data voltage VDATA is input.

[0004] To solve the above problems, existing technologies employ... Figures 1a-1b The pixel circuit shown compensates for the threshold voltage Vth of the driving transistor, but Figure 1a The pixel circuit of the 6T1C shown has too many components, which reduces the PPI (Pixels Per Inch) of the display panel. Figure 1b The 4T2C pixel circuit shown has a brief current flow through the light-emitting element in stages other than the light-emitting stage. This not only affects the display effect but also increases the power consumption of the pixel circuit.

[0005] Therefore, a new pixel circuit needs to be proposed to solve the above problems. Summary of the Invention

[0006] In view of the above problems, the purpose of the present invention is to provide a pixel circuit and its driving method, as well as a display device and its display panel, which can not only solve the problem of uneven display brightness of the display panel caused by the manufacturing process, but also reduce power consumption.

[0007] According to one aspect of the present invention, a pixel circuit is provided, comprising a first thin-film transistor for transmitting a data voltage; a second thin-film transistor connected to the first thin-film transistor at a node for providing a driving current based on a node voltage of the node and a first power supply voltage; a light-emitting element for emitting light under the drive current; and a compensation module connected between the first power supply voltage and ground, and connected to the node, for storing a threshold voltage of the second thin-film transistor at the node during a threshold voltage acquisition phase, superimposing the threshold voltage and a voltage related to the data voltage into a driving voltage at the node during a grayscale voltage writing phase, and providing the driving voltage to the second thin-film transistor during an emission phase to generate a driving current, wherein the data voltage is set to the grayscale voltage during the grayscale voltage writing phase, and the first power supply voltage is in a high-impedance state during both the threshold voltage acquisition phase and the grayscale voltage writing phase.

[0008] Optionally, the pixel circuit further includes a preset stage prior to the threshold voltage acquisition stage and a reset stage prior to the preset stage. The compensation module is configured to reset the node voltage to the data voltage in the reset stage and charge the node voltage to the data voltage in the preset stage, wherein the data voltage is set to an initial voltage in the reset stage and the data voltage is set to a preset voltage in the preset stage.

[0009] Optionally, the first power supply voltage is in a high-impedance state during the reset phase and the preset phase.

[0010] Optionally, the initial voltage has a ground voltage.

[0011] Optionally, the preset voltage is greater than the grayscale voltage.

[0012] Optionally, a first terminal of the first thin-film transistor receives the data voltage, a second terminal of the first thin-film transistor is connected to the node, and a control terminal of the first thin-film transistor receives a first control signal; a first terminal of the second thin-film transistor receives the first power supply voltage, a second terminal of the second thin-film transistor provides the drive current, and a control terminal of the second thin-film transistor is connected to the node; a first terminal of the light-emitting element receives the drive current, and a second terminal of the light-emitting element receives a second power supply voltage, wherein the first power supply voltage is greater than the second power supply voltage.

[0013] Optionally, the compensation module includes: a first capacitor and a second capacitor, which are connected sequentially between the node and ground; a third thin-film transistor, whose first end receives the first power supply voltage, whose second end is connected to the node, and whose control end receives a second control signal; and a fourth thin-film transistor, whose first end is connected to the common node of the first capacitor and the second capacitor, whose second end is grounded, and whose control end receives a third control signal.

[0014] According to a second aspect of the present invention, a display panel is provided, comprising a plurality of pixel circuits as described above arranged in an array.

[0015] According to a third aspect of the present invention, a display device is provided, comprising: a display panel as described above; and a source drive circuit for providing a data voltage to the display panel.

[0016] According to a fourth aspect of the present invention, a method for driving a pixel circuit is provided for driving the pixel circuit as described in any one of claims 1-7, comprising:

[0017] During the reset phase, the first thin-film transistor and the fourth thin-film transistor are turned on. The first thin-film transistor transmits the initial voltage, which serves as the data voltage, to a node to reset the node voltage of the node, as well as the first capacitor and the second capacitor, to the initial voltage.

[0018] In the preset phase, the first thin-film transistor and the fourth thin-film transistor are turned on, and the data voltage is set to a preset voltage to charge the node voltage to the preset voltage, thereby turning on the second thin-film transistor;

[0019] During the threshold voltage acquisition phase, the third thin-film transistor, the second thin-film transistor, and the fourth thin-film transistor are turned on to discharge the node voltage to the threshold voltage of the second thin-film transistor.

[0020] During the grayscale voltage writing stage, the first thin-film transistor and the second thin-film transistor are turned on, and the data voltage is set to the grayscale voltage so that the node voltage is the driving voltage formed by the superposition of the threshold voltage and the voltage related to the grayscale voltage.

[0021] During the light-emitting phase, the second thin-film transistor provides a driving current according to the driving voltage and the first power supply voltage to drive the light-emitting element to emit light.

[0022] The first power supply voltage is in a high-impedance state during the reset phase, the preset phase, the threshold voltage acquisition phase, and the grayscale voltage writing phase.

[0023] The pixel circuit, driving method, display device, and display panel provided in this invention solve the problem of uneven display caused by differences in the distribution of the threshold voltage of the second thin-film transistor due to manufacturing process in the threshold voltage acquisition stage. This is achieved by storing the threshold voltage of the second thin-film transistor in a node during the threshold voltage acquisition stage, superimposing the threshold voltage and a voltage related to the grayscale voltage into a driving voltage stored in the node during the grayscale voltage writing stage, and providing a driving current independent of its threshold voltage to drive the light-emitting element to emit light during the light-emitting stage based on the driving voltage and the first power supply voltage. Furthermore, this pixel circuit requires only 4T2C, which, compared to the 6T1C structure of the prior art, can improve the PPI of the display panel. The first power supply voltage is in a high-impedance state during all stages except the light-emitting stage, preventing transient current flow through the light-emitting element that could cause brief light emission and affect the display effect. It also reduces the power consumption of the pixel circuit, making it significantly lower than the 4T2C structure of the prior art. Attached Figure Description

[0024] The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0025] Figures 1a-1b A circuit diagram of a prior art pixel circuit is shown;

[0026] Figure 2 A circuit connection diagram of a pixel circuit according to an embodiment of the present invention is shown;

[0027] Figure 3 A signal timing diagram of a pixel circuit according to an embodiment of the present invention is shown. Detailed Implementation

[0028] Various embodiments of the invention will now be described in more detail with reference to the accompanying drawings. In the various drawings, the same elements or modules are indicated by the same or similar reference numerals. For clarity, the various parts in the drawings are not drawn to scale.

[0029] It should be understood that, in the following description, "circuit" may include single or combined hardware circuits, programmable circuits, state machine circuits, and / or elements capable of storing instructions executed by the programmable circuit. When an element or circuit is said to be "connected" to another element or "connected" between two nodes, it may be directly coupled or connected to the other element, or there may be intermediate elements; the connection between elements may be physical, logical, or a combination thereof. Conversely, when an element is said to be "directly coupled to" or "directly connected" to another element, it means that there are no intermediate elements between them.

[0030] Furthermore, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0031] This invention provides a display device, which includes a display panel and a source driving circuit that provides data voltage to the display panel. The display panel includes a plurality of pixel circuits arranged in an array, and each pixel circuit receives the data voltage provided by the source driving circuit through a corresponding data line.

[0032] Figure 2 A circuit connection diagram of a pixel circuit according to an embodiment of the present invention is shown. See also Figure 2 The pixel circuit includes thin-film transistor T1, thin-film transistor T2, compensation module 10, and light-emitting element 20.

[0033] The first terminal of the thin-film transistor T1 receives the data voltage VDATA, and the second terminal of the thin-film transistor T1 is connected to node A via the compensation module 10. The control terminal of the thin-film transistor T1 receives the control signal G1. The switching on and off of the thin-film transistor T1 is controlled by the control signal G1, which is used to transmit the data voltage VDATA to node A when it is on.

[0034] The compensation module 10 is connected between the first power supply voltage ELVDD and ground GND. It receives the data voltage VDATA through node A. During the threshold voltage acquisition stage, it stores the threshold voltage Vth of the thin-film transistor T2 in node A. During the grayscale voltage writing stage following the threshold voltage acquisition stage, it superimposes the threshold voltage Vth and the voltage related to the data voltage VDATA to form a driving voltage, which is stored in node A. Finally, during the light emission stage following the grayscale voltage writing stage, it provides the driving voltage to the control terminal of the thin-film transistor T2. In the threshold voltage acquisition stage, the data voltage is the grayscale voltage Vgary corresponding to the grayscale data.

[0035] The first terminal of the thin-film transistor T2 receives the first power supply voltage ELVDD (emission layer VDD), the second terminal of the thin-film transistor T2 is connected to the first terminal of the light-emitting element 20, and the control terminal of the thin-film transistor T2 is connected to node A. The thin-film transistor T2 is the driving transistor of the pixel circuit, and its conduction and cutoff are controlled by the driving voltage. It is used to provide a driving current Ids according to the driving voltage and the first power supply voltage ELVDD during the light-emitting stage to drive the light-emitting element 20 to emit light.

[0036] The first terminal of the light-emitting element 20 is connected to the second terminal of the thin-film transistor T2, and the second terminal of the light-emitting element 20 is connected to the second power supply voltage ELVSS (emission layer VSS). The light-emitting element 20 is, for example, an organic light-emitting diode (OLED), with its first terminal being the anode of the OLED and its second terminal being the cathode of the OLED. It is understood that the light-emitting element 20 of the present invention is not limited to OLED, but can also be an LED, etc.

[0037] The compensation module 10 includes a thin-film transistor T3, a thin-film transistor T4, a capacitor C1, and a capacitor C2. The first terminal of the thin-film transistor T3 receives a first power supply voltage ELVDD. The second terminal of the thin-film transistor T3 is connected to the first terminal of the capacitor C1, i.e., node A. The control terminal of the thin-film transistor T3 receives a control signal G2. The second terminal of the capacitor C1 is connected to the first terminal of the capacitor C2, and the second terminal of the capacitor C2 is grounded to GND. The first terminal of the thin-film transistor T4 is connected to the second terminal of the capacitor C1, and the second terminal of the thin-film transistor T4 is grounded to GND. The control terminal of the thin-film transistor T4 receives a control signal G3.

[0038] In this embodiment, thin-film transistors T1-T4 are all N-type thin-film transistors, where the first terminal can be the drain and the second terminal can be the source. Of course, thin-film transistors T1-T4 can also all be P-type thin-film transistors, or some can be N-type and some P-type. This can be achieved by simply changing the port polarities of the selected types of thin-film transistors T1-T4 in the connections according to the port polarities of the thin-film transistors T1-T4 in this embodiment.

[0039] Figure 3 A signal timing diagram of a pixel circuit according to an embodiment of the present invention is shown. See also Figure 3A single light-emitting cycle of a pixel circuit includes a reset phase ①, a preset phase ②, a threshold voltage catch phase ③, a grayscale voltage write phase ④, and an emission phase ⑤. In phases ①-④, the first power supply voltage ELVDD is in a high-impedance state (HIZ), at which time no current flows through thin-film transistors T2-T3. In emission phase ⑤, the first power supply voltage ELVDD is greater than the second power supply voltage ELVSS.

[0040] See Figure 2 as well as Figure 3 During the reset phase ①, control signals G1 and G3 are both high, control signal G2 is low, and the data voltage VDATA is set to the ground voltage GND, i.e., 0V. Then, thin film transistors T1 and T4 are both turned on, thin film transistor T3 is turned off, the voltage at the second terminal of thin film transistor T1, i.e., the voltage at node A, is reset to 0V, and the voltages of capacitors C1 and C2 are also reset to 0V. At this time, since the voltage at node A is 0V, thin film transistor T2 is turned off.

[0041] In the preset stage ②, control signals G1 and G3 are both high level, control signal G2 is low level, and the data voltage VDATA is set to the preset voltage Vofs. Then, thin film transistors T1 and T4 are both turned on, thin film transistor T3 is turned off, and capacitor C1 is charged to the preset voltage Vofs, that is, node A is charged to the preset voltage Vofs. At this time, since the preset voltage Vofs is greater than the threshold voltage Vth, thin film transistor T2 is turned on.

[0042] In the threshold voltage catch (Vth catch) stage ③, control signal G1 is low and control signals G2-G3 are high. Therefore, thin film transistor T1 is turned off, and thin film transistors T3 and T4 are both turned on. At this time, thin film transistor T3 connects the first terminal and the control terminal of thin film transistor T2, making thin film transistor T2 equivalent to a diode to discharge node A until the voltage of node A is equal to the threshold voltage Vth of thin film transistor T2. In this stage, since the control terminal voltage of thin film transistor T2 is never less than its threshold voltage Vth, thin film transistor T2 remains in the conducting state.

[0043] In the grayscale voltage writing stage ④, control signal G1 is high, control signals G2-G3 are low, and the data voltage VDATA is set to the grayscale voltage Vgary. Therefore, thin-film transistor T1 is turned on, while thin-film transistors T3 and T4 are turned off. At this time, the voltage across capacitor C1, i.e., the voltage at node A, is Vth + Vgary * C2 / (C1 + C2). Therefore, thin-film transistor T2 remains on. The grayscale voltage Vgary is less than the preset voltage Vofs.

[0044] During the light-emitting stage ⑤, control signals G1-G3 are all low, so thin-film transistors T1, T3, and T4 are all off. At this time, the first power supply voltage ELVDD is no longer in a high-impedance state, and the voltage at node A remains Vth + Vgary*C2 / (C1 + C2). Thin-film transistor T2 remains on, providing a drive current Ids to the light-emitting element 20 to drive it to emit light. Since the voltage across capacitor C2 is Vgary*C1 / (C1 + C2) at this time, the drive current provided by thin-film transistor T2... Where K is the intrinsic conductivity factor of thin-film transistor T2.

[0045] According to the formula, during the light-emitting stage ⑤, the driving current Ids provided by the thin-film transistor T2 to the light-emitting element 20 is independent of its threshold voltage Vth. Therefore, the distribution difference of the threshold voltage Vth of the thin-film transistor T2 caused by the manufacturing process is eliminated, which can make the display brightness of the display panel uniform and improve the display effect of the display panel.

[0046] The pixel circuit, driving method, display device, and display panel provided in this invention solve the problem of uneven display caused by the distribution difference of the threshold voltage Vth of the thin-film transistor T2 due to the manufacturing process. This is achieved by storing the threshold voltage Vth of the thin-film transistor T2 at node A during the threshold voltage acquisition stage, superimposing the threshold voltage Vth and the voltage related to the grayscale voltage Vgary into a driving voltage at node A during the grayscale voltage writing stage, and providing a driving current Ids independent of its threshold voltage Vth according to the driving voltage and the first power supply voltage ELVDD during the light-emitting stage to drive the light-emitting element 20 to emit light. Furthermore, this pixel circuit requires only 4T2C, which, compared to the 6T1C structure of the prior art, can improve the PPI of the display panel. The first power supply voltage ELVDD is in a high-resistance state during all stages except the light-emitting stage, preventing transient current flow through the light-emitting element and its impact on the display effect. This also reduces the power consumption of the pixel circuit, making it more power-efficient than the 4T2C structure of the prior art.

[0047] As described above, these embodiments of the present invention do not exhaustively describe all details, nor do they limit the invention to specific embodiments. Clearly, many modifications and variations can be made based on the above description. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to effectively utilize the invention and its modifications. The scope of protection of this invention should be determined by the scope defined in the claims and their equivalents.

Claims

1. A pixel circuit, comprising: a first thin film transistor configured to transmit a data voltage; a second thin film transistor connected to a node with the first thin film transistor, configured to provide a driving current according to a node voltage of the node and a first power voltage; a light emitting element configured to emit light under driving of the driving current; a compensation module connected between the first power voltage and a ground and connected to the node, configured to store a threshold voltage of the second thin film transistor in the node in a threshold voltage acquisition stage, to store a driving voltage obtained by superimposing the threshold voltage and a voltage related to the data voltage in the node in a gray scale voltage writing stage, and to provide the driving voltage to the second thin film transistor to make it generate the driving current in a light emitting stage, wherein the data voltage is set as a gray scale voltage in the gray scale voltage writing stage, and the first power voltage is in a high resistance state in both the threshold voltage acquisition stage and the gray scale voltage writing stage, the pixel circuit further comprises a preset stage before the threshold voltage acquisition stage, and a reset stage before the preset stage, and the compensation module is configured to reset the node voltage to the data voltage in the reset stage, and to charge the node voltage to the data voltage in the preset stage, wherein the data voltage is set as an initial voltage in the reset stage, and the data voltage is set as a preset voltage in the preset stage.

2. The pixel circuit of claim 1, wherein, the first power voltage is in a high resistance state in the reset stage and the preset stage.

3. The pixel circuit of claim 1, wherein, the initial voltage has a ground voltage.

4. The pixel circuit of claim 3, wherein, the preset voltage is greater than the gray scale voltage. 5.The pixel circuit of claim 1, wherein a first end of the first thin film transistor receives the data voltage, a second end of the first thin film transistor is connected to the node, and a control end of the first thin film transistor receives a first control signal; a first end of the second thin film transistor receives the first power voltage, a second end of the second thin film transistor provides the driving current, and a control end of the second thin film transistor is connected to the node; a first end of the light emitting element receives the driving current, and a second end of the light emitting element receives a second power voltage, wherein the first power voltage is greater than the second power voltage.

6. The pixel circuit of claim 1, wherein, the compensation module comprises: a first capacitor and a second capacitor connected between the node and the ground in sequence; a third thin film transistor having a first end receiving the first power voltage, a second end connected to the node, and a control end receiving a second control signal; a fourth thin film transistor having a first end connected to a common node of the first capacitor and the second capacitor, a second end grounded, and a control end receiving a third control signal. 7.A display panel, comprising a plurality of pixel circuits as claimed in any one of claims 1-6 arranged in an array. 8.A display device, comprising: the display panel as claimed in claim 7; and a source driving circuit configured to provide a data voltage to the display panel. 9.A driving method of a pixel circuit, configured to drive the pixel circuit as claimed in any one of claims 1-6, comprising: In the reset stage, the first thin film transistor and the fourth thin film transistor are turned on, and an initial voltage as a data voltage is transmitted to a node by the first thin film transistor to reset a node voltage of the node and the first capacitor and the second capacitor to the initial voltage; In the preset stage, the first thin film transistor and the fourth thin film transistor are turned on, and the data voltage is set to a preset voltage to charge the node voltage to the preset voltage, so that the second thin film transistor is turned on; In the threshold voltage acquisition stage, the third thin film transistor, the second thin film transistor and the fourth thin film transistor are turned on to discharge the node voltage to a threshold voltage of the second thin film transistor; In the gray scale voltage writing stage, the first thin film transistor and the second thin film transistor are turned on, and the data voltage is set to a gray scale voltage, so that the node voltage is a driving voltage obtained by superimposing the threshold voltage and a voltage related to the gray scale voltage; In the light emitting stage, the second thin film transistor provides a driving current according to the driving voltage and a first power supply voltage to drive the light emitting element to emit light, wherein the first power supply voltage is in a high resistance state in the reset stage, the preset stage, the threshold voltage acquisition stage and the gray scale voltage writing stage.

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