A pixel circuit, a display panel and a display device
By adding an eighth thin-film transistor T8 and a Voffset signal line to the 7T1C structure, the red pixel can be turned on at low gray levels, solving the problem of the light-emitting element's color being too green at low gray levels and improving the display effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BOE TECHNOLOGY GROUP CO LTD
- Filing Date
- 2023-07-28
- Publication Date
- 2026-05-19
AI Technical Summary
In low grayscale conditions, red pixels of the light-emitting element are difficult to light up, resulting in a greenish tint to the displayed color and affecting the display effect.
Based on the original 7T1C structure, an eighth thin-film transistor T8 and a Voffset signal line are added. The eighth thin-film transistor T8 is turned on for voltage compensation when the gray level is low, so as to ensure that the red pixel can be lit up at low gray levels.
It improves the display effect of display devices at low grayscale and solves the problem of green color deviation caused by the difficulty in activating red pixels.
Smart Images
Figure CN116863862B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of display technology, and in particular to a pixel circuit, a display panel, and a display device. Background Technology
[0002] Currently, the material properties of light-emitting elements make it difficult for red pixels to light up at low grayscale levels, resulting in slow response and a greenish tint in the displayed color. This leads to display problems such as ghosting and poor image quality.
[0003] Therefore, improving the red pixel response capability of light-emitting elements is crucial for enhancing the display effect of low grayscale, but no effective solution has yet been proposed for this problem. Summary of the Invention
[0004] In view of this, this application provides a pixel circuit, a display panel, and a display device to solve the technical problem that red pixels are difficult to light up under low grayscale conditions of light-emitting elements.
[0005] In a first aspect, embodiments of this application provide a pixel circuit, including: a light-emitting driving circuit, a light-emitting element, an eighth thin-film transistor, and a constant voltage terminal; wherein, the light-emitting driving circuit provides a driving current to the light-emitting element; the first electrode of the eighth thin-film transistor is connected to the light-emitting element, the control electrode of the eighth thin-film transistor is connected to the data signal line of the light-emitting driving circuit, and the second electrode of the eighth thin-film transistor is connected to the constant voltage terminal.
[0006] In one possible implementation, the threshold voltage of the eighth thin-film transistor is less than the difference between a first voltage and a second voltage; the first voltage is the activation voltage of the red pixel of the light-emitting element; and the second voltage is the voltage at a constant voltage terminal.
[0007] In one possible implementation, the voltage of the data signal line of the light-emitting driving circuit is greater than or equal to a first voltage, and the eighth thin-film transistor is turned on.
[0008] In one possible implementation, the voltage of the data signal line of the light-emitting driving circuit is less than the first voltage, and the eighth thin-film transistor is turned off.
[0009] In one possible implementation, the eighth thin-film transistor is an N-type thin-film transistor.
[0010] In one possible implementation, the light-emitting driving circuit includes seven thin-film transistors and a storage capacitor.
[0011] Secondly, embodiments of this application provide a display panel including the pixel circuit described in the above embodiments.
[0012] Thirdly, embodiments of this application provide a display device, including: a brightness adjustment component, a voltage adjustment module, and a display panel as described in the above embodiments;
[0013] The brightness adjustment component is configured to generate a brightness adjustment signal in response to a brightness adjustment operation.
[0014] The voltage adjustment module is configured to adjust the voltage of the data signal line of the light-emitting driving circuit of the pixel circuit of the display panel according to the brightness adjustment signal.
[0015] In one possible implementation, when the voltage of the data signal line is greater than or equal to a first voltage, the eighth thin-film transistor in the pixel circuit of the display panel is turned on; the constant voltage terminal in the pixel circuit of the display panel compensates the voltage of the light-emitting driving circuit, thereby illuminating the red pixel of the light-emitting element; the first voltage is the activation voltage of the red pixel of the light-emitting element.
[0016] In one possible implementation, when the voltage of the data signal line is less than a first voltage, the eighth thin-film transistor in the pixel circuit of the display panel is turned off.
[0017] The pixel circuit of this application can activate the red pixel when the light-emitting element is at a low grayscale, thus solving the technical problem of the light-emitting element having a greenish tint at low grayscale. Attached Figure Description
[0018] Figure 1 This is a functional structure diagram of the pixel circuit in an embodiment of this application;
[0019] Figure 2 This is a detailed circuit diagram of the pixel circuit in an embodiment of this application;
[0020] Figure 3 This is a timing diagram of the pixel circuit in an embodiment of this application;
[0021] Figure 4 This is a functional structure diagram of a display device according to an embodiment of this application. Detailed Implementation
[0022] Various embodiments and features of this application are described herein with reference to the accompanying drawings.
[0023] It should be understood that various modifications can be made to the embodiments described herein. Therefore, the above description should not be considered as limiting, but merely as an example of embodiments. Other modifications within the scope and spirit of this application will be apparent to those skilled in the art.
[0024] The accompanying drawings, which are included in and form part of this specification, illustrate embodiments of the present application and, together with the general description of the present application given above and the detailed description of the embodiments given below, serve to explain the principles of the present application.
[0025] These and other features of this application will become apparent from the following description of preferred forms of embodiments given as non-limiting examples, with reference to the accompanying drawings.
[0026] It should also be understood that although this application has been described with reference to some specific examples, those skilled in the art can certainly implement many other equivalent forms of this application.
[0027] The above and other aspects, features and advantages of this application will become more apparent when taken in conjunction with the accompanying drawings and in view of the following detailed description.
[0028] Specific embodiments of this application are described thereafter with reference to the accompanying drawings; however, it should be understood that the claimed embodiments are merely examples of this application, which can be implemented in various ways. Well-known and / or repeated functions and structures are not described in detail to avoid unnecessary or redundant details that could obscure the application. Therefore, the specific structural and functional details claimed herein are not intended to be limiting, but merely serve as the basis and representative basis for the claims to teach those skilled in the art to use this application in a variety of substantially any suitable detailed structures.
[0029] This specification may use the phrases “in one embodiment,” “in another embodiment,” “in yet another embodiment,” or “in other embodiments,” all of which may refer to one or more of the same or different embodiments according to this application.
[0030] First, a brief introduction to the design concept of the embodiments of this application will be given.
[0031] Unlike traditional rigid screens, flexible screens do not use rigid glass as a substrate. Instead, they use organic materials as a flexible base. Through thin-film encapsulation technology and a protective film adhered to the back of the panel, the panel becomes bendable and less prone to breakage. Compared to traditional screens, flexible screens offer significant advantages, including being thinner and lighter, consuming less power, and thus improving device battery life.
[0032] The light-emitting element of flexible screens is an organic light-emitting diode (OLED). The main direction for improving flexible screens is to reduce power consumption. It is necessary to consider the response capability of the light-emitting element and the differences in R / G / B light-emitting materials. The influence of device crosstalk determines that the above two characteristics are contradictory. Therefore, how to improve the response capability of the light-emitting element while keeping the crosstalk level of the light-emitting element unchanged and the relative difference of monochromaticity before and after reliability is small has become a major challenge for the improvement of flexible screens.
[0033] One specific problem is that when the organic light-emitting diode is in a low grayscale, the red pixels are not lit while the green pixels are lit, resulting in a greenish tint and poor display effect of the flexible screen.
[0034] To address this, this application utilizes the LTPO (Low Temperature Polycrystalline Oxide) process to provide a pixel circuit with an 8T1C (8 thin-film transistors, 1 capacitor C) structure. An eighth thin-film transistor T8 and a Voffset constant voltage signal line are added to the anode of the original 7T1C (7 thin-film transistors, 1 capacitor C) circuit. At low grayscale levels, the eighth thin-film transistor T8 is turned on, allowing the voltage of the Voffset signal line to compensate for the light emission of the organic light-emitting diode. At high grayscale levels, the eighth thin-film transistor T8 is turned off, without affecting the original 7T1C circuit. The function of the eighth thin-film transistor T8 is as a control switch for voltage compensation.
[0035] In this application, the pixel circuit turns on the eighth thin-film transistor T8 at low grayscale levels to compensate the anode of the 7T1C circuit with the voltage of the Voffset signal line, thereby activating the red pixel at low grayscale levels and solving the technical problem of greenish color caused by the difficulty in activating the red pixel at low grayscale levels; thus improving the display effect of the display device.
[0036] After introducing the application scenarios and design concepts of the embodiments of this application, the technical solutions provided by the embodiments of this application will be described below.
[0037] like Figure 1 As shown, this application provides a pixel circuit, including: a light-emitting driving circuit, a light-emitting element, an eighth thin-film transistor, and a constant voltage terminal; wherein, the light-emitting driving circuit provides a driving current for the light-emitting element; the first electrode of the eighth thin-film transistor is connected to the light-emitting element, the control electrode of the eighth thin-film transistor is connected to the data signal line of the light-emitting driving circuit, and the second electrode of the eighth thin-film transistor is connected to the constant voltage terminal.
[0038] For example, such as Figure 2 As shown, the light-emitting driving circuit adopts a 7T1C circuit structure, namely seven thin-film transistors (TFTs) and one storage capacitor (C). The light-emitting element is an organic light-emitting diode (OLED).
[0039] It is particularly important to note that for a thin-film transistor, the first electrode can be either the drain or the source. When the first electrode is the drain, the second electrode can be the source, and vice versa. In the thin-film transistor of this embodiment, the first electrode is the drain, the second electrode is the source, and the control electrode is the gate.
[0040] exist Figure 2 In the light-emitting driving circuit, the connection relationships of each component are as follows:
[0041] The control electrode of the first thin-film transistor T1 receives the reset signal Reset_P; the first electrode of the first thin-film transistor T1 is connected to the first initial voltage Vint1 (negative voltage); the second electrode of the first thin-film transistor T1 is connected to one end of the capacitor Cst; the other end of the capacitor Cst is connected to the first power supply terminal VDD.
[0042] The control electrode of the fifth thin-film transistor T5 receives the control light emission signal EM, the second electrode of the fifth thin-film transistor T5 is connected to the first power supply terminal VDD, and the first electrode of the fifth thin-film transistor T5 is connected to the second electrode of the third thin-film transistor T3.
[0043] The control electrode of the third thin-film transistor T3 is connected between the capacitor Cst and the first thin-film transistor T1; the first electrode of the third thin-film transistor T3 is connected to the second electrode of the sixth thin-film transistor T2.
[0044] The control electrode of the sixth thin-film transistor T6 receives the control light emission signal EM, the first electrode of the sixth thin-film transistor T6 is connected to the organic light-emitting diode OLED, and the organic light-emitting diode OLED is connected to the second power supply terminal VSS.
[0045] The control electrode of the second thin-film transistor T2 receives the first gate signal Gate_N, and the first electrode of the second thin-film transistor T2 is connected between the access point of T3 and the first thin-film transistor T1; the second electrode access point of the second thin-film transistor T2 is located between the third thin-film transistor T3 and the sixth thin-film transistor T6.
[0046] The control electrode of the fourth thin-film transistor T4 is connected to the second gate signal Gate_P. The first electrode of the fourth thin-film transistor T4 is connected between the fifth thin-film transistor T5 and the third thin-film transistor T3. The second electrode of the fourth thin-film transistor T4 is connected to the data signal line (the voltage is represented by Vdata); where Vdata ranges from 1 to 6.8V; it is used to control the switching of the third thin-film transistor T3.
[0047] The control electrode of the seventh thin-film transistor T7 receives the second gate signal Gate_P; the second electrode of the seventh thin-film transistor T7 is connected between the sixth thin-film transistor T6 and the organic light-emitting diode OLED; and the first electrode of the seventh thin-film transistor T7 is connected to the second initial voltage Vint2 (negative voltage).
[0048] Based on the above 7T1C circuit structure, specifically, as follows: Figure 2 As shown, in this embodiment, the first electrode of the eighth thin-film transistor T8 is connected between the seventh thin-film transistor T7 and the organic light-emitting diode OLED; the control electrode of the thin-film transistor is connected to the data signal line, and the constant voltage terminal is the VOffset signal line that provides a constant voltage; the second electrode of the thin-film transistor is connected to the VOffset signal line.
[0049] When the eighth thin-film transistor T8 and VOffset signal lines are not connected, the operating timing of the light-emitting driving circuit is as follows:
[0050] First stage (reset stage): The control electrode of the first thin film transistor T1 receives the reset signal Reset_P, and the first thin film transistor T1 turns on. The control electrode of the third thin film transistor T3 receives the first initial voltage Vinit1, and the third thin film transistor T3 turns on.
[0051] Second stage (compensation stage): The first thin-film transistor T1 is turned off, the control electrode of the second thin-film transistor T2 receives the first gate signal Gate_N, and the second thin-film transistor T2 is turned on; the control electrodes of the fourth thin-film transistor T4 and the seventh thin-film transistor T7 receive the second gate signal Gate_P, and both the fourth thin-film transistor T4 and the seventh thin-film transistor T7 are turned on; the voltage Vdata of the data signal line is written to the third thin-film transistor T3 until the voltage reaches Vdata+Vth3, where Vth3 is the threshold voltage of the third thin-film transistor T3; at the same time, the capacitor Cst is charged.
[0052] The third stage (light emission stage): the fourth thin film transistor T4 and the seventh thin film transistor T7 are turned off, and the second thin film transistor T2 is turned off; the control electrode of the fifth thin film transistor T5 and the control electrode of the sixth thin film transistor receive the light emission signal EM, and the fifth thin film transistor T5 and the sixth thin film transistor T6 are both turned on, then the first power supply terminal VDD and the second power supply terminal VSS are turned on, and the organic light emission diode OLED emits light.
[0053] To activate the red pixel of an OLED at low grayscale, the first step is to adjust the voltage Vdata on the data signal line to obtain the initial voltage Vdata0 for the red pixel. This is a critical voltage: when Vdata is less than Vdata0, the red pixel is lit; as Vdata increases, when Vdata becomes greater than or equal to Vdata0, the red pixel changes from lit to off. Alternatively, when Vdata is greater than or equal to Vdata0, the red pixel is off; as Vdata decreases, when Vdata becomes less than Vdata0, the red pixel changes from off to lit.
[0054] Therefore, in the specific implementation of the pixel circuit, the voltage Voffset of the VOffset signal line can be set to any voltage value less than Vdata0. Once the voltage of the VOffset signal line is determined, the eighth thin-film transistor T8 can be selected, which needs to satisfy the condition that its threshold voltage is greater than the difference between Vdata0 and Voffset.
[0055] Preferably, to reduce leakage current in the third thin-film transistor T3, the second thin-film transistor T2 is an N-type thin-film transistor. The first thin-film transistor T1, the third thin-film transistor T3, the fourth thin-film transistor T4, the fifth thin-film transistor T5, the sixth thin-film transistor T6, and the seventh thin-film transistor T7 are all P-type thin-film transistors. The eighth thin-film transistor T8 is an N-type thin-film transistor.
[0056] The implementation of the pixel circuit in this application requires the addition of a VOffset constant voltage signal trace in the AA (Active Area) region. The process is similar to that of the anode power supply VDD. All designs can be implemented using existing LTPO 7T1C circuits and existing processes. Depending on the actual needs, this design can be added separately to the red or blue pixels without affecting the green pixels.
[0057] As can be seen, since the voltage Voffset is fixed, the voltage Vdata of the data signal line is the voltage that controls the switch of the eighth thin-film transistor T8. That is, when the voltage Vdata of the data signal line is less than Vdata0, the organic light-emitting diode OLED is in a high grayscale and the voltage of the data signal line is at a low potential. At this time, the voltage difference VGS of the eighth thin-film transistor T8 is equal to Vdata minus Voffset. The voltage difference VGS is less than the threshold voltage Vth of the eighth thin-film transistor T8, so the eighth thin-film transistor T8 is normally off. The voltage of the VOffset signal line cannot be written to the anode of the 7T1C circuit. The working timing of the organic light-emitting diode OLED is the same as that of the conventional 7T1C circuit.
[0058] When the voltage Vdata on the data signal line is greater than or equal to Vdata0, the OLED is in a low grayscale, and the voltage on the data signal line is at a high potential. At this time, the voltage difference VGS of the eighth thin-film transistor T8 is greater than the threshold voltage Vth, the eighth thin-film transistor T8 is turned on, and the voltage of the VOffset signal line is written to the anode of the 7T1C circuit, causing the red pixel of the OLED to light up. Tests show that the larger Vdata is, the lower the grayscale and the better the compensation effect.
[0059] Therefore, the threshold voltage Vth of the thin-film transistor is less than the difference between the first voltage Vdata0 and the voltage Voffset of the VOffset signal line; wherein, the first voltage is the turn-on voltage of the red pixel of the organic light-emitting diode OLED.
[0060] In summary, when the voltage of the data signal line is greater than or equal to the first voltage, the thin-film transistor is turned on, and the voltage of the VOffset signal line is written into the anode of the light-emitting driving circuit for voltage compensation. When the voltage of the data signal line is less than the first voltage, the thin-film transistor is turned off.
[0061] like Figure 3 As shown, the operating timing of the pixel circuit in this embodiment is as follows:
[0062] First stage: The control electrode of the first thin-film transistor T1 receives the reset signal Reset_P, and the first thin-film transistor T1 turns on. The control electrode of the third thin-film transistor T3 receives the first initial voltage Vinit1, and the third thin-film transistor T3 turns on.
[0063] Second stage: The first thin-film transistor T1 is turned off, the control electrode of the second thin-film transistor T2 receives the first gate signal Gate_N, and the second thin-film transistor T2 is turned on; the control electrodes of the fourth thin-film transistor T4 and the seventh thin-film transistor T7 receive the second gate signal Gate_P, and both the fourth thin-film transistor T4 and the seventh thin-film transistor T7 are turned on; the voltage Vdata of the data signal line is written to the third thin-film transistor T3 until Vdata+Vth3, where Vth3 is the threshold voltage of the third thin-film transistor T3; at the same time, the capacitor Cst is charged;
[0064] Phase 3: The fourth thin-film transistor (TFT) T4 and the seventh TFT T7 are off, as is the second TFT T2. The control electrodes of the fifth and sixth TFTs receive the light-emitting signal EM. Both the fifth and sixth TFTs T6 are on, causing the first power supply terminal VDD and the second power supply terminal VSS to conduct, resulting in OLED light emission. When the data signal line voltage Vdata is greater than or equal to the first voltage Vdata0, the OLED is in a low grayscale. At this time, the voltage difference VGS of the eighth TFT T8 is greater than the threshold voltage Vth, so the eighth TFT T8 is on. The voltage of the VOffset signal line is written to the anode, illuminating the red pixels of the OLED. When the data signal line voltage Vdata is less than the first voltage Vdata0, the OLED is in a high grayscale. At this time, the voltage difference VGS of the eighth TFT T8 is less than the threshold voltage Vth, so the eighth TFT T8 is off, and the voltage of the VOffset signal line does not affect the original circuit.
[0065] Based on the same inventive concept, this embodiment provides a display panel including the pixel circuit of the above embodiment.
[0066] Preferably, the display panel in this embodiment is an organic light-emitting diode (OLED) display panel, such as a flexible screen. The display panel in this embodiment has the same technical effects as the pixel circuit.
[0067] Based on the same inventive concept, embodiments of this application provide a display device, such as... Figure 4 As shown, it includes: a brightness adjustment component, a voltage adjustment module, and a display panel as described in the above embodiment;
[0068] The brightness adjustment component is configured to generate a brightness adjustment signal in response to a brightness adjustment operation.
[0069] The voltage adjustment module is configured to adjust the voltage of the data signal line of the light-emitting driving circuit of the pixel circuit of the display panel according to the brightness adjustment signal.
[0070] Furthermore, when the voltage of the data signal line is greater than or equal to the first voltage, the eighth thin-film transistor in the pixel circuit of the display panel is turned on; the constant voltage terminal in the pixel circuit of the display panel compensates the voltage of the light-emitting driving circuit, thereby illuminating the red pixel of the light-emitting element; the first voltage is the activation voltage of the red pixel of the light-emitting element.
[0071] When the voltage of the data signal line is less than the first voltage, the eighth thin-film transistor in the pixel circuit of the display panel is turned off.
[0072] Figure 4 The display device shown is for illustrative purposes only. The display device can be any electronic device with display function, such as an in-vehicle display device, mobile phone, tablet computer, laptop computer, monitor or television. The embodiments in this application are not specifically limited.
[0073] For example, when the display device is a mobile phone, tablet computer, or laptop computer, the brightness adjustment operation is to slide the brightness display bar; when the display device is a monitor or television, the brightness adjustment operation is to press the brightness adjustment button.
[0074] Since the display device in this embodiment has a pixel circuit, when the brightness is adjusted to a low grayscale, the eighth thin-film transistor T8 is turned on to compensate the voltage of the Voffset signal line for the anode of the light-emitting driving circuit, thereby turning on the red pixel of the light-emitting element at a low grayscale, thus improving the display effect of the display device at a low grayscale; while at a high grayscale, the eighth thin-film transistor T8 is turned off, and the Voffset signal line voltage does not affect the light-emitting driving circuit.
[0075] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.
[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.
Claims
1. A pixel circuit, characterized in that, include: The light-emitting driving circuit, the light-emitting element, the eighth thin-film transistor, and the constant voltage terminal; wherein, the light-emitting driving circuit provides driving current to the light-emitting element; The first electrode of the eighth thin-film transistor is connected to the light-emitting element, the control electrode of the eighth thin-film transistor is connected to the data signal line of the light-emitting driving circuit, and the second electrode of the eighth thin-film transistor is connected to the constant voltage terminal. The threshold voltage of the eighth thin-film transistor is less than the difference between the first voltage and the second voltage; the first voltage is the turn-on voltage of the red pixel of the light-emitting element; the second voltage is the voltage at the constant voltage terminal.
2. The pixel circuit according to claim 1, characterized in that, When the voltage of the data signal line of the light-emitting driving circuit is greater than or equal to the first voltage, the eighth thin-film transistor is turned on.
3. The pixel circuit according to claim 1, characterized in that, When the voltage of the data signal line of the light-emitting driving circuit is less than the first voltage, the eighth thin-film transistor is turned off.
4. The pixel circuit according to claim 1, characterized in that, The eighth thin-film transistor is an N-type thin-film transistor.
5. The pixel circuit according to claim 1, characterized in that, The light-emitting driving circuit includes seven thin-film transistors and a storage capacitor.
6. A display panel, characterized in that, Including the pixel circuit of any one of claims 1-5.
7. A display device, characterized in that, include: Brightness adjustment component, voltage adjustment module, and display panel of claim 6; The brightness adjustment component is configured to generate a brightness adjustment signal in response to a brightness adjustment operation. The voltage adjustment module is configured to adjust the voltage of the data signal line of the light-emitting driving circuit of the pixel circuit of the display panel according to the brightness adjustment signal; When the voltage of the data signal line is greater than or equal to the first voltage, the eighth thin-film transistor in the pixel circuit of the display panel is turned on; the constant voltage terminal in the pixel circuit of the display panel compensates the voltage of the light-emitting driving circuit, so that the red pixel of the light-emitting element is lit. The first voltage is the activation voltage of the red pixel of the light-emitting element.
8. The display device according to claim 7, characterized in that, When the voltage of the data signal line is less than the first voltage, the eighth thin-film transistor in the pixel circuit of the display panel is turned off.