CN104134427A - Pixel circuit - Google Patents

Abstract

A pixel circuit comprises an energy storage element, a driving transistor, a first transistor, a second transistor, a third transistor, a fourth transistor and a fifth transistor. The first end of the first transistor is electrically connected with the first end of the energy storage element. The first terminal of the second transistor is used for selectively receiving a data voltage or a precharge voltage. The grid of the third transistor and the grid of the second transistor are used for receiving a scanning signal. The grid of the fifth transistor and the grid of the fourth transistor are used for receiving a light-emitting energy signal. By the technical means of the invention, under the condition of providing the same data voltage, even if the critical voltage of the driving transistor generates deviation, the same driving current can be generated to drive the light-emitting element. Therefore, the phenomenon of uneven brightness of the display picture can be improved.

Description

pixel circuit

technical field

The present invention relates to a pixel circuit, and in particular to a pixel driving circuit suitable for organic light emitting diodes.

Background technique

Flat panel display devices have the advantages of low power consumption, low heat generation, light weight, etc., and have been widely used in various electronic products. Flat panel display devices can generally be classified into passive matrix and active matrix according to their driving methods. The passive-matrix display device is limited by its driving mode, and has disadvantages such as short lifespan and incapability of being large-scaled. Although the cost of the active matrix display device is more expensive and the manufacturing process is more complicated, it can meet the display requirements of large size and high resolution. Therefore, active matrix display devices have become the mainstream of flat panel display devices. Among them, the active organic light-emitting diode (Organic Light-Emitting Diode, OLED) display device is one of the main products developed by various manufacturers in recent years.

However, in thin-film transistors used in active organic light-emitting diode display devices, the driving transistor used to drive the organic light-emitting diode may have a bias in the threshold voltage of the transistor due to factors such as different manufacturing processes, materials, or device characteristics. shift, so that under the same data voltage driving, the driving current of the organic light emitting diode of each pixel will be slightly different. In addition, the current flowing through the OLED will also change as the power supply voltage is affected by the line resistance drop (IR-Drop). The above factors will cause uneven brightness of the display screen of the OLED display device.

Contents of the invention

Therefore, one aspect of the present invention is to provide a pixel circuit. The pixel circuit includes an energy storage element, a driving transistor, a first transistor, a second transistor and a third transistor. The gate of the driving transistor is electrically connected to the first end of the energy storage element. The first terminal of the first transistor is electrically connected with the first terminal of the energy storage element. The gate of the first transistor, the second terminal of the first transistor and the first terminal of the driving transistor are electrically connected. The first terminal of the second transistor is used for selectively receiving a data voltage or a precharge voltage. The second terminal of the second transistor is electrically connected with the second terminal of the energy storage element. The gate of the third transistor and the gate of the second transistor are used for receiving a scan signal. The first terminal of the third transistor is electrically connected with the second terminal of the driving transistor. The second terminal of the third transistor is electrically connected with the first terminal of the energy storage element. In a first stage, the potential of the second terminal of the energy storage element is maintained at a reference voltage. In a second stage, the first terminal of the second transistor is used to receive the precharge voltage. The second transistor and the third transistor are turned on according to the scanning signal, so that the energy storage element is charged by the precharge voltage through the second transistor, and the first transistor is turned on corresponding to the charging operation of the energy storage element.

Another aspect of the present invention is to provide a pixel circuit. The pixel circuit includes an energy storage element, a driving transistor, a first transistor, a second transistor, a third transistor, a fourth transistor and a fifth transistor. The gate of the driving transistor is electrically connected to the first end of the energy storage element. The first terminal of the first transistor is electrically connected with the first terminal of the energy storage element. The gate of the first transistor, the second terminal of the first transistor and the first terminal of the driving transistor are electrically connected. The first terminal of the second transistor is used for selectively receiving a data voltage or a precharge voltage. The second terminal of the second transistor is electrically connected with the second terminal of the energy storage element. The gate of the third transistor and the gate of the second transistor are used for receiving a scan signal. The first terminal of the third transistor is electrically connected with the second terminal of the driving transistor. The second terminal of the third transistor is electrically connected with the first terminal of the energy storage element. The first terminal of the fourth transistor is electrically connected with the second terminal of the energy storage element. The second end of the fourth transistor is electrically connected to a reference voltage. The first terminal of the fifth transistor is electrically connected with the second terminal of the driving transistor. The gate of the fifth transistor and the gate of the fourth transistor are used for receiving a light-emitting enabling signal.

Through the technical means of the present invention, since the driving current for driving the light-emitting element to emit light has nothing to do with the critical voltage of the driving transistor, under the condition of providing the same data voltage, even if the critical voltage of the driving transistor is shifted, it can still be achieved by the present invention. The pixel circuit generates the same drive current to drive the light emitting element. In this way, the problem that the driving transistor in the pixel circuit may be shifted due to factors such as different manufacturing processes, materials, or device characteristics can be solved, and the uneven brightness of the display screen of the organic light-emitting diode display device can be improved. The phenomenon.

In addition, since the driving current for driving the light-emitting element to emit light has nothing to do with the supply voltage, it can solve the situation that the supply voltage is inconsistent with the driving current caused by the line resistance drop (IR-Drop) under different pixels. In this way, the picture uniformity of a high-resolution panel using a large number of pixels can be effectively improved.

Furthermore, the pixel circuit proposed by the present invention only needs to use two driving signals, so it can provide a larger pixel wiring space than the known pixel compensation circuit, and can increase the aperture ratio of the display device. In this way, it is easier to meet the requirements of high-resolution and narrow border (slim border) panels, and can further improve the life of the light-emitting elements.

Description of drawings

FIG. 1 is a schematic circuit diagram of a pixel circuit in an embodiment of the present invention;

2A is a schematic diagram illustrating a pixel driving circuit in a first stage according to an embodiment of the present invention;

FIG. 2B is a schematic diagram illustrating signals driving a pixel circuit in a first stage according to an embodiment of the present invention;

3A is a schematic diagram illustrating a driving pixel circuit in a second stage according to an embodiment of the present invention;

FIG. 3B is a schematic diagram illustrating signals driving a pixel circuit in a second stage according to an embodiment of the present invention;

4A is a schematic diagram illustrating a driving pixel circuit in a third stage according to an embodiment of the present invention;

FIG. 4B is a schematic diagram illustrating signals driving a pixel circuit in a third stage according to an embodiment of the present invention;

5A is a schematic diagram illustrating a driving pixel circuit in a fourth stage according to an embodiment of the present invention;

FIG. 5B is a schematic diagram illustrating signals driving a pixel circuit in a fourth stage according to an embodiment of the present invention;

6 is a schematic circuit diagram of a pixel circuit in an embodiment of the present invention;

7 is a schematic circuit diagram of a pixel circuit in an embodiment of the present invention;

FIG. 8 is a schematic circuit diagram of a pixel circuit in an embodiment of the present invention.

Detailed ways

The following is a detailed description of the embodiments in conjunction with the accompanying drawings, but the provided embodiments are not intended to limit the scope of the present invention, and the description of the structure and operation is not intended to limit the order of execution, and any recombination of components The structure of the resulting device with equal efficacy is within the scope of the present invention. In addition, the drawings are for illustration purposes only and are not drawn to original scale. For ease of understanding, the same components will be described with the same symbols in the following description.

Unless otherwise specified, the terms used throughout the specification and claims generally have the ordinary meaning of each term as used in the art, in this disclosure and in the special context. Certain terms used to describe the present invention are discussed below or elsewhere in this specification to provide those skilled in the art with additional guidance in describing the present invention.

In addition, as used herein, "coupling" or "connection" may refer to two or more elements being in direct physical or electrical contact with each other, or indirect physical or electrical contact with each other, or referring to two or more components. Multiple elements operate or act on each other.

In this article, "a" and "the" can generally refer to a single or a plurality, unless the article is specifically limited in the context. It will be further understood that "comprises", "comprises", "has" and similar words used herein indicate the features, regions, integers, steps, operations, elements and/or components described therein, but do not exclude One or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof described or additional thereto.

In addition, in this document, it is understandable that terms such as first, second and third are used to describe various elements, components, regions, layers and/or blocks. But these elements, components, regions, layers and/or blocks should not be limited by these terms. These terms are limited to identifying a single element, component, region, layer and/or block. Therefore, a first element, component, region, layer and/or block hereinafter may also be referred to as a second element, component, region, layer and/or block without departing from the spirit of the present invention.

Please refer to Figure 1. FIG. 1 is a schematic circuit diagram of a pixel circuit 100 in an embodiment of the present invention.

The pixel circuit 100 includes an energy storage element Cst, a driving transistor TD, a first transistor T1 , a second transistor T2 , a third transistor T3 , a fourth transistor T4 and a fifth transistor T5 .

The gate of the driving transistor TD is electrically connected to the energy storage element Cst. In one embodiment, the energy storage element Cst is a capacitor, and the gate of the driving transistor TD is electrically connected to the terminal E with the first end of the energy storage element Cst. The first terminal of the first transistor T1 and the first terminal of the energy storage element Cst are electrically connected to the terminal E, and the gate of the first transistor T1, the second terminal of the first transistor T1 and the first terminal of the driving transistor TD are electrically connected to each other. is connected to terminal F, and receives a supply voltage OVDD from terminal F. The first end of the second transistor T2 is used for selectively receiving a data voltage or a pre-charging voltage from the terminal A. In one embodiment, the level of the precharge voltage is higher than the level of the data voltage, and the data voltage may come from the output of a data driving circuit (not shown). The second terminal of the second transistor T2 is electrically connected to the terminal D with the second terminal of the energy storage element Cst. The gate of the third transistor T3 and the gate of the second transistor T2 are used for receiving a scan signal from the terminal B. The first terminal of the third transistor T3 is electrically connected with the second terminal of the driving transistor TD. The second terminal of the third transistor T3 is electrically connected to the terminal E with the first terminal of the energy storage element Cst. The first terminal of the fourth transistor T4 is electrically connected to the terminal D with the second terminal of the energy storage element Cst. The second end of the fourth transistor T4 is electrically connected to a reference voltage Vref. The first end of the fifth transistor T5 is electrically connected to the second end of the driving transistor TD. The gate of the fifth transistor T5 and the gate of the fourth transistor T4 are used for receiving a light-emitting enabling signal from the terminal C. In this embodiment, the pixel circuit 100 further includes a light emitting element 110 . The light emitting element 110 is electrically connected to the second terminal of the fifth transistor T5. In one embodiment, the light emitting element 110 is an organic light emitting diode (Organic Light Emitting Diode, OLED), the anode of the organic light emitting diode is electrically connected to the second end of the fifth transistor T5, and the cathode of the organic light emitting diode is connected to A DC bias voltage OVSS.

In addition, in one embodiment, the driving transistor TD, the first transistor T1, the second transistor T2, the third transistor T3, the fourth transistor T4 and the fifth transistor T5 are all P-type transistors, and the first terminals of the transistors are The source (Source) of the P-type transistor, and the second terminal of the transistor is the drain (Drain) of the P-type transistor.

The following FIGS. 2A , 2B, 3A, 3B, 4A, 4B, 5A and 5B are used to illustrate the operation process of the pixel circuit 100 . FIG. 2A , FIG. 3A , FIG. 4A and FIG. 5A are schematic diagrams of driving the pixel circuit 100 in different stages respectively. 2B , FIG. 3B , FIG. 4B and FIG. 5B are schematic diagrams of signals used to drive the pixel circuit 100 at the stages corresponding to FIG. 2A , FIG. 3A , FIG. 4A and FIG. 5A , respectively. In Figure 2A, Figure 3A, Figure 4A and Figure 5A, endpoint A is used to receive the signal 120 in Figure 2B, Figure 3B, Figure 4B, and Figure 5B respectively, and endpoint B is used to receive Figure 2B, Figure 3B, and Figure 4B respectively , the scanning signal SCAN in FIG. 5B , and the terminal C are respectively used to receive the light-enabling signal EM in FIG. 2B , FIG. 3B , FIG. 4B , and FIG. 5B . The voltage Vg in FIG. 2B , FIG. 3B , FIG. 4B , and FIG. 5B is respectively the gate voltage of the driving transistor TD in FIG. 2A , FIG. 3A , FIG. 4A and FIG. 5A . In addition, in FIG. 2A , FIG. 3A , FIG. 4A and FIG. 5A , the transistors in the dotted line indicate that the transistors are not turned on.

As shown in FIG. 2A and FIG. 2B , before a first stage L1 of driving the pixel circuit 100 starts, the light-emitting enable signal EM received by the terminal C is at a low level voltage. Therefore, the fourth transistor T4 is turned on, and the potential of the second terminal of the energy storage element Cst is maintained at the reference voltage Vref at the terminal D through the fourth transistor T4 . In the first stage L1, the light-emitting enable signal EM received by the terminal C changes from a low level voltage to a high level voltage. Therefore, the fourth transistor T4 and the fifth transistor T5 are turned off according to the light-emitting enable signal EM, and the potential of the second terminal of the energy storage element Cst is still maintained at the reference voltage Vref at the terminal D. In addition, because the scan signal SCAN received by the terminal B has a high level voltage, the second transistor T2 and the third transistor T3 are not turned on. The signal 120 received by the terminal A is maintained at a precharge voltage Vpre.

Referring to FIG. 3A and FIG. 3B , in a second stage L2 of driving the pixel circuit 100 , the scanning signal SCAN received by the terminal B changes from a high level voltage to a low level voltage. The second transistor T2 and the third transistor T3 are turned on according to the scan signal SCAN. Since the second transistor T2 is turned on, the energy storage element Cst is charged by the precharge voltage Vpre of the terminal A via the second transistor T2 . Wherein, the potential of the second terminal of the energy storage element Cst (ie, the potential of the terminal D) is charged from the reference voltage Vref to the precharge voltage Vpre. Due to the feed-through effect of the capacitor, the potential of the first terminal of the energy storage element Cst (ie, the potential of the terminal E) also rises accordingly. Therefore, the transistor T1 is turned on, and the energy storage element Cst is discharged through the first transistor T1 as shown in the direction of the dotted arrow in FIG. 3A . The potential value of the first terminal of the energy storage element Cst (ie, the potential value of the terminal E) will be discharged to about OVDD+|Vth|, where Vth is the threshold voltage of the driving transistor TD.

Next, please refer to FIG. 4A and FIG. 4B , when the pixel circuit 100 is driven in a third stage L3, the signal 120 received by the terminal A drops from the precharge voltage Vpre to a data voltage Vdata. Therefore, the potential of the second terminal of the energy storage element Cst (ie, the potential of the terminal D) is discharged from the precharge voltage Vpre to the data voltage Vdata through the second transistor T2. Due to the feed-through effect of the capacitor, the potential of the first terminal of the energy storage element Cst (ie, the potential of the terminal E) also decreases accordingly. Accordingly, the transistor T1 is turned off, and since the gate potential of the driving transistor TD drops below OVDD−|Vth|, the driving transistor TD is turned on. As shown in the direction of the dotted arrow in FIG. 4A , the energy storage element Cst is charged by the supply voltage OVDD through the drive transistor TD and the third transistor T3, so that the potential value of the first terminal of the energy storage element Cst (that is, the potential value of the terminal E potential value) is charged to an operating voltage OVDD-|Vth|.

Please refer to FIG. 5A and FIG. 5B , when driving the pixel circuit 100 in a fourth stage L4 (that is, the display stage), the scanning signal SCAN received by the terminal B changes from a low level voltage to a high level voltage, and the terminal C The received light-emitting enable signal EM changes from a high level voltage to a low level voltage. The second transistor T2 and the third transistor T3 are turned off according to the scanning signal SCAN, and the fourth transistor T4 and the fifth transistor T5 are turned on according to the light-emitting enable signal EM. The potential of the second terminal of the energy storage element Cst (ie, the potential of the terminal D) is discharged from the data voltage Vdata to the reference voltage Vref through the fourth transistor T4. Due to the feedthrough effect of the capacitor, the potential of the first terminal of the energy storage element Cst (ie, the potential of the terminal E) also drops to about OVDD-|Vth|-Vdata+Vref, and thus the driving transistor TD is turned on. Since both the driving transistor TD and the fifth transistor T5 are turned on, the light emitting element 110 is driven by the supply voltage OVDD via the driving transistor TD and the fifth transistor T5 to emit light. Wherein, the driving current for driving the light emitting element 110 to emit light is the driving current Id output by the second terminal of the driving transistor TD. The driving current Id is determined by the following mathematical formula:

Id=K*(Vs-Vg-|Vth|)^2

＝K*(OVDD-(OVDD-|Vth|-Vdata+Vref)-|Vth|)^2

=K*(Vdata-Vref)^2

Wherein, K is the current constant of the driving transistor TD, Vs is the potential of the first terminal of the driving transistor TD, and Vg is the potential of the gate of the driving transistor TD (ie, the potential of the terminal E). It can be known from the above formula that the present invention selectively receives the data voltage or the precharge voltage from the terminal A by using the first terminal of the second transistor T2, and utilizes the feedthrough effect of the capacitor to drive the light emitting element 110 to emit light during the display phase. The driving current Id is only related to the data voltage Vdata and the reference voltage Vref. The driving current Id has nothing to do with the threshold voltage Vth of the driving transistor TD, and the driving current Id has nothing to do with the supply voltage OVDD.

It should be noted that the above pixel circuit 100 shown in FIGS. 1 to 5B is only an exemplary embodiment of the present invention, and is not intended to limit the present invention. For example, although in the pixel circuit 100, each transistor is implemented by using a P-type transistor, those skilled in the art can follow the teachings of the above-mentioned exemplary embodiments to deduce/deduce the modification of implementing by using an N-type transistor. Therefore, without departing from the spirit and scope of the present invention, these variant implementations should also belong to the protection category of the present invention. In addition, FIG. 6 to FIG. 8 respectively illustrate variants of the pixel circuit proposed by the present invention.

In the pixel circuit 600 shown in FIG. 6, the terminal I is used to receive the signal 120 shown in FIG. 2B to FIG. 5B, and the terminal J is used to receive the scanning signal SCAN shown in FIG. 2B to FIG. 5B, The terminal K is used to receive the light-enabling signal EM as shown in FIGS. 2B to 5B . The operation of the pixel circuit 600 is similar to that of the pixel circuit 100 shown in FIGS. 1 to 5B , so it will not be repeated here.

In the pixel circuit 700 shown in FIG. 7, the terminal L is used to receive the signal 120 shown in FIG. 2B to FIG. 5B, and the terminal M is used to receive the scanning signal SCAN shown in FIG. 2B to FIG. 5B, The terminal N is used to receive the light-enabling signal EM as shown in FIGS. 2B to 5B . The operation of the pixel circuit 700 is similar to that of the pixel circuit 100 shown in FIGS. 1 to 5B , so details will not be repeated here.

In the pixel circuit 800 shown in FIG. 8, the terminal P is used to receive the signal 120 shown in FIG. 2B to FIG. 5B, and the terminal Q is used to receive the scanning signal SCAN shown in FIG. 2B to FIG. 5B, The terminal R is used for receiving the light enabling signal EM as shown in FIGS. 2B to 5B . The operation of the pixel circuit 800 is similar to that of the pixel circuit 100 shown in FIGS. 1 to 5B , so details will not be repeated here.

To sum up, through the technical means of the present invention, since the driving current for driving the light-emitting element to emit light has nothing to do with the critical voltage of the driving transistor, under the condition of providing the same data voltage, even if the critical voltage of the driving transistor shifts, it can still The same driving current is generated by the pixel circuit proposed by the present invention to drive the light emitting element. In this way, the problem that the driving transistor in the pixel circuit may be shifted due to factors such as different manufacturing processes, materials, or device characteristics can be solved, and the uneven brightness of the display screen of the organic light-emitting diode display device can be improved. The phenomenon.

In addition, since the driving current for driving the light-emitting element to emit light has nothing to do with the supply voltage OVDD, it can solve the situation that the supply voltage is inconsistent with the driving current caused by the line resistance drop (IR-Drop) under different pixels. In this way, the picture uniformity of a high-resolution panel using a large number of pixels can be effectively improved.

Furthermore, the pixel circuit proposed by the present invention only needs to use two driving signals, so it can provide a larger pixel wiring space and increase the aperture ratio of the display device. In this way, it is easier to meet the requirements of high-resolution and narrow border (slim border) panels, and can further improve the life of the light-emitting elements.

Although the present invention has been disclosed above in terms of implementation, it is not intended to limit the present invention. Any skilled person can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the present invention The scope of protection should be based on the scope defined by the appended claims.

Claims (10)

1. A pixel circuit, characterized in that, comprising: an energy storage element; a drive transistor, the gate of the drive transistor is electrically connected to the first end of the energy storage element; A first transistor, the first end of the first transistor is electrically connected to the first end of the energy storage element, the gate of the first transistor, the second end of the first transistor and the first end of the driving transistor electrical connection; a second transistor, the first end of the second transistor is used to selectively receive a data voltage or a pre-charge voltage, the second end of the second transistor is electrically connected to the second end of the energy storage element; and A third transistor, the gate of the third transistor and the gate of the second transistor are used to receive a scanning signal, the first end of the third transistor is electrically connected with the second end of the driving transistor, the third The second end of the transistor is electrically connected to the first end of the energy storage element; wherein in a first phase, the potential of the second terminal of the energy storage element is maintained at a reference voltage; In a second stage, the first terminal of the second transistor is used to receive the precharge voltage, the second transistor and the third transistor are turned on according to the scanning signal, so that the energy storage element passes through the second transistor The precharge voltage is charged, and the first transistor is turned on corresponding to the charging operation of the energy storage element. 2 . The pixel circuit according to claim 1 , wherein in a third stage, the first end of the second transistor is used to receive the data voltage, and the second end of the energy storage element passes through the second transistor. is discharged to the data voltage. 3. The pixel circuit according to claim 2, wherein in the third phase, the driving transistor is turned on, and the energy storage element is further charged by a supply voltage through the driving transistor and the third transistor , so that the first end of the energy storage element is charged to an operating voltage. 4. The pixel circuit according to claim 1 or 2, further comprising: a fourth transistor, the first end of the fourth transistor is electrically connected to the second end of the energy storage element, and the second end of the fourth transistor is electrically connected to the reference voltage; and A fifth transistor, the first end of the fifth transistor is electrically connected to the second end of the driving transistor, the gate of the fifth transistor and the gate of the fourth transistor are used to receive a light-emitting enable signal, the The second end of the fifth transistor is used to electrically connect a light emitting element; In a fourth phase, the second transistor and the third transistor are turned off according to the scan signal, the fourth transistor and the fifth transistor are turned on according to the light-emitting enabling signal, and the second terminal of the energy storage element is passed through The fourth transistor is discharged to the reference voltage. 5. The pixel circuit according to claim 4, wherein in the fourth stage, both the drive transistor and the fifth transistor are turned on, so that the light-emitting element is supplied by a supply via the drive transistor and the fifth transistor. Light is driven by voltage. 6. The pixel circuit according to any one of claims 1-5, wherein the level of the precharge voltage is higher than that of the data voltage. 7. A pixel circuit, characterized in that it comprises: an energy storage element; a drive transistor, the gate of the drive transistor is electrically connected to the first end of the energy storage element; A first transistor, the first end of the first transistor is electrically connected to the first end of the energy storage element, the gate of the first transistor, the second end of the first transistor and the first end of the driving transistor electrical connection; a second transistor, the first end of the second transistor is used to selectively receive a data voltage or a pre-charge voltage, the second end of the second transistor is electrically connected to the second end of the energy storage element; A third transistor, the gate of the third transistor and the gate of the second transistor are used to receive a scanning signal, the first end of the third transistor is electrically connected with the second end of the driving transistor, the third The second end of the transistor is electrically connected to the first end of the energy storage element; a fourth transistor, the first end of the fourth transistor is electrically connected to the second end of the energy storage element, and the second end of the fourth transistor is electrically connected to a reference voltage; and A fifth transistor, the first terminal of the fifth transistor is electrically connected with the second terminal of the driving transistor, the gate of the fifth transistor and the gate of the fourth transistor are used for receiving a light-emitting enabling signal. 8. The pixel circuit according to claim 7, further comprising: A light emitting element, the light emitting element is electrically connected with the second end of the fifth transistor. 9. The pixel circuit according to claim 8, wherein the light emitting element is an organic light emitting diode, and the driving transistor, the first transistor, the second transistor, the third transistor, the fourth transistor and The fifth transistors are all P-type transistors. 10. The pixel circuit according to any one of claims 7-9, wherein the level of the precharge voltage is higher than that of the data voltage.