CN104167168B - Image element circuit and driving method thereof and display device - Google Patents

Abstract

The present invention provides a pixel circuit, a driving method thereof, and a display device, comprising: a first switch unit, a second switch unit, a third switch unit, a fourth switch unit, a fifth switch unit, a drive unit, an energy storage unit and An electroluminescent unit, the control terminals of the first switch unit and the fifth switch unit are connected to the second scanning signal line; the control terminals of the second switch unit, the third switch unit and the fourth switch unit are connected to The first scan signal line. The pixel circuit provided by the invention can thoroughly solve the problem of uneven display brightness caused by the drift of the threshold voltage of the driving transistor. At the same time, in the present invention, there are only two switch signal input lines, which not only saves energy consumption, but also reduces the interference between the lines.

Description

Pixel circuit, driving method thereof, and display device

technical field

The present invention relates to the field of display technology, in particular to a pixel circuit, a driving method thereof, and a display device.

Background technique

Organic light-emitting display (OLED) is one of the hot spots in the field of flat panel display research. Compared with liquid crystal display, OLED has the advantages of low energy consumption, low production cost, self-illumination, wide viewing angle and fast response speed. At present, OLEDs have begun to replace traditional liquid crystal (LCD) displays in display fields such as mobile phones, PDAs, and digital cameras. Pixel drive circuit design is the core technical content of OLED display, which has important research significance.

Unlike TFT (Thin Film Field Effect Transistor)-LCD, which uses a stable voltage to control brightness, OLED is current-driven and requires a stable current to control light emission.

Due to the process and device aging, in the original 2T1C driving circuit (including two thin film field effect transistors and a capacitor), there is non-uniformity in the threshold voltage of the driving TFT of each pixel, which leads to the Changes in the current of each pixel OLED make the display brightness uneven, thereby affecting the display effect of the entire image.

Contents of the invention

The object of the present invention is to solve the problem of uneven display brightness of a display device, reduce the number of signal lines used for pixel circuits in the display device, reduce the cost of integrated circuits, and increase the pixel density of the display device at the same time.

In order to achieve the above object, the present invention provides a pixel circuit, including a first switch unit, a second switch unit, a third switch unit, a fourth switch unit, a fifth switch unit, a drive unit, an energy storage unit and an electroluminescent unit;

The first terminal of the energy storage unit is connected to the control terminal of the drive unit, and is used to pull up the voltage of the control terminal of the drive unit to make the drive unit work; the input terminal of the drive unit is connected to the anode of the electroluminescence unit, and is used to drive the electric Luminescent unit for luminescent display;

The first switch unit is connected between the input terminal of the driving unit and the working voltage line, and the control terminal is connected to the second scanning signal line for providing a driving voltage to the driving unit under the control of the second scanning signal line;

The second switch unit is connected between the input end of the drive unit and the first end of the energy storage unit, and the control end is connected to the first scanning signal line, for charging the energy storage unit under the control of the first scanning signal line discharge;

The third switch unit is connected between the second end of the energy storage unit and the data signal line, and the control end is connected to the first scanning signal line for writing the voltage in the data signal line into the the second end of the energy storage unit;

The first terminal of the fourth switch unit is connected between the output terminal of the driving unit and the anode of the electroluminescent unit, the second terminal is grounded, and the control terminal is connected to the first scanning signal line, which is used to connect the first scanning signal line to the first scanning signal line. short-circuiting the electroluminescence unit under control;

The fifth switch unit is connected between the anode of the electroluminescent unit and the second terminal of the energy storage unit, and the control terminal is connected to the second scanning signal line, which is used to make the energy storage unit operate under the control of the second scanning signal line. The electroluminescent cell is discharged.

Preferably, each switch unit and the drive unit are thin film field effect transistors, the control terminal of each switch unit is a gate, and the other two ends correspond to source and drain; the input terminal of the drive unit is a drain, and the control terminal The terminal is the gate, and the output terminal is the source.

Preferably, each thin film field effect transistor is an N-channel type.

Preferably, the energy storage unit is a capacitor.

Preferably, the electroluminescence unit is an organic light emitting diode.

The present invention also provides a driving method for a pixel circuit, which is used to drive the pixel circuit described in any one of the above, wherein each frame working period includes a charging phase, a discharging phase and a light emitting phase, wherein,

In the charging stage, apply a voltage to the scanning signal line to turn on all the switch units, so that the working voltage line charges the first end of the energy storage unit;

In the discharge phase, applying a voltage to the scanning signal line to conduct the second switch unit, the third switch unit, and the fourth switch unit, and applying a data voltage to the data signal line to discharge the first end of the energy storage unit;

In the light-emitting phase, a voltage is applied to the scanning signal line to turn on the first switch unit and the fifth switch unit, so that the electroluminescent unit emits light.

Preferably, when each switch unit in the pixel circuit is an N-channel thin film field effect transistor, the method includes:

In the charging phase, a high-level signal is applied to both the first scanning signal line and the second scanning signal line;

In the discharge phase, a high-level signal is applied to the first scanning signal line;

In the light-emitting phase, a high-level signal is applied to the second scanning signal line.

Preferably, after the discharge phase and before the light-emitting phase, a voltage stabilization phase is also included,

In the voltage stabilizing phase, a voltage is applied to the scanning signal line to turn off all switching units.

The present invention also provides a display device, comprising the pixel circuit described in any one of the above items.

In the pixel circuit provided by the present invention, the operating current flowing through the electroluminescent unit is not affected by the threshold voltage of the corresponding driving transistor, which completely solves the problem of uneven display brightness caused by the drift of the threshold voltage of the driving transistor. At the same time, in the present invention, there are only two switch signal input lines, which not only saves energy consumption, but also reduces the interference between the lines.

Description of drawings

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

FIG. 2 is a timing diagram of key signals in a pixel circuit provided by an embodiment of the present invention;

FIG. 3 is a schematic diagram of current flow and voltage values of a pixel circuit in different timings in an embodiment of the present invention.

detailed description

The specific implementation manners of the present invention will be further described below in conjunction with the drawings and examples. The following examples are only used to illustrate the technical solution of the present invention more clearly, but not to limit the protection scope of the present invention.

An embodiment of the present invention provides a pixel circuit, as shown in Figure 1 or Figure 3, including:

Five switching units T1, T2, T3, T4, T5, one driving unit DT, one energy storage unit C, and one electroluminescent unit L;

The control terminals of T1 and T5 are connected to the second scanning signal line Scan[2]; the first terminal of T1 is connected to the working voltage line V _dd , and the second terminal is connected to the input terminal of the driving unit DT; the first terminal of T5 Connected to the output terminal of DT, and its second terminal is connected to the second terminal B of the energy storage unit C;

The control terminals of T2, T3 and T4 are all connected to the first scanning signal line Scan[1]; the first terminal of T2 is connected to the input terminal of DT, and the second terminal thereof is connected to the first terminal A of the energy storage unit C; The first end of T3 is connected to the data signal line Data, and the second end thereof is connected to the second end B of the energy storage unit C; the first end of T4 is connected to the output end of DT, and the second end thereof is grounded;

The output terminal of DT is also connected with the anode of the electroluminescence unit L, and its control terminal is connected with the A terminal of the energy storage unit.

It can be understood that, in the present invention, the control terminals are connected to a plurality of switch units of the same scan signal line (two switch units T2, T3, T4 connected to Scan[1], two switch units connected to Scan[2] Units T1, T5) should be switches of the same channel type, that is, both high-level conduction or both low-level conduction, so as to ensure the conduction or shutdown of the two switch units connected to the same scanning signal line The status is the same.

In the pixel circuit provided by the present invention, the operating current flowing through the electroluminescent unit is not affected by the threshold voltage of the corresponding driving transistor, which completely solves the problem of uneven display brightness caused by the drift of the threshold voltage of the driving transistor. At the same time, in the present invention, there are only two switch signal input lines, which not only saves energy consumption, but also reduces the interference between the lines.

Preferably, each switching unit and driving unit is a thin film field effect transistor TFT, the control terminal of each switching unit is a gate, the first terminal of each switching unit is a drain of TFT, and the second terminal of each switching unit is a source of TFT. pole; the input end of the driving unit is the drain of the TFT, the control end is the gate of the TFT, and the output end is the source of the TFT. Of course, the switch unit and the drive unit may also be other suitable devices or a combination of devices.

It is not difficult to understand that the transistors corresponding to the driving unit and the switching unit here can be transistors whose source and drain can be interchanged, or according to different conduction types, the first end of each switching unit and driving unit may be the drain of the transistor, The second terminal is the source of the transistor. Those skilled in the art can obtain the same source and drain of each transistor in the pixel circuit provided by the present invention without any creative work. Circuit structures with the same or similar technical effects achieved by the technical solution should also fall within the protection scope of the present invention.

Further, in the embodiment of the present invention, all thin film field effect transistors are N-channel type. Using the same type of transistors can realize the unification of process flow, thereby improving the yield rate of products. Those skilled in the art can understand that, in practical applications, the types of each transistor may not be exactly the same, for example, T2, T3 and T4 may be N-channel transistors, and T1 and T5 may be P-channel transistors, As long as the on/off states of the two switch units whose control terminals are connected to the same scanning signal line can be made the same, the technical solution provided by this application can be realized. limited.

Preferably, the energy storage unit C is a capacitor. Of course, in practical applications, other components with energy storage functions can also be used according to design requirements.

Preferably, the electroluminescence unit L may be an organic light emitting diode (OLED). Of course, in practical applications, other elements with electroluminescence function can also be used according to design requirements.

The driving method of the pixel circuit provided by the preferred embodiment of the present invention will be described in detail below in conjunction with Fig. 2 and Fig. 3. As shown in Fig. 2, the timing sequence of the scanning signal input to each scanning signal line when the pixel circuit provided by the present invention is in operation The diagram can be divided into four stages, which are respectively represented as reset stage W1, discharge stage W2, voltage stabilization stage W3, and light-emitting stage W4 in Fig. 2. In each stage, the current flow direction and voltage value of the pixel circuit are shown in Fig. 3a , Figure 3b, Figure 3c. For convenience of description, it is assumed that each switch unit is an N-channel TFT.

In the reset phase W1, as shown in Figure 2, both Scan[1] and Scan[2] are at a high level, and V _data is applied to the data voltage line Data (V _data is the data voltage required to make the OLED emit light this time. ), at this time all TFTs are turned on, as shown in Figure 3a, V _dd charges to point A along T1 and T2 until the voltage at point A reaches V _dd ; because T3 is turned on, point B is connected to the data voltage line Data, and the potential is V _data .

The purpose of this stage is to reset the voltage at point A and keep the voltage at point A at a higher potential, so that the voltage at point A can be changed to a lower level through appropriate control in the subsequent process. Reasonable potential. Since this process is mainly to reset the voltage at point A, there is no requirement for the voltage at point B, so the voltage in the data voltage line Data can also be other voltages (such as zero voltage).

In the discharge phase W2, as shown in Figure 2, Scan[1] is at high level, Scan[2] is at low level, and continues to apply V _data on the data signal line Data. At this time, T2, T3, T4 is turned on, T1 and T5 are turned off, as shown in Figure 3b, the capacitor C discharges along T2-DT-T4 until the voltage drops to V _th , that is, the potential of point A drops to V _th after the discharge, and the potential of point B The potential is still V _data , where V _th is the threshold voltage of DT. The purpose of this stage is to make the voltage at point A become a voltage related to the threshold voltage V _th of DT, so that it can be offset with the threshold voltage V _th of DT in the subsequent light-emitting stage, and the influence of threshold voltage V _th drift on the flow through Influence of the current of the electroluminescent cell. In addition, at this stage, the voltage at point B is set to the data voltage V _data , and affects the current flowing through the electroluminescent element L in the final light-emitting stage, so that the electroluminescent element L emits light correspondingly, so this stage actually The above is also the writing phase of the data voltage.

In the voltage stabilization phase W3, as shown in Figure 2, both Scan[1] and Scan[2] are at low level, and all TFTs are turned off at this time. This process takes a relatively short time, mainly for the discharge phase W2. After the discharge is sufficient, it plays the role of stabilizing the voltage difference (V _th -V _data ) between point A and point B. Those skilled in the art can understand that this process is to better stabilize the pressure difference between point A and point B as V _th -V _data , even if this stage is missing, the technical solution provided by the present invention can also be implemented, the present invention The preferred embodiments should not be construed as limiting the protection scope of the present invention.

In the light-emitting phase W4, Scan[1] is at low level, and Scan[2] is at high level. At this time, T1 and T5 are turned on, and T2, T3 and T4 are turned off. Referring to Fig. 3c, the potential change at point B is V _data →V _{oled_in} (V _{oled_in} is the turn-on voltage of the electroluminescence unit L, after T5 is turned on, the voltage at the B terminal of the capacitor C is consistent with the anode voltage of L, that is is V _{oled_in} ), because terminal A is floating, V _A and V _B achieve equal voltage jumps (keep the original voltage difference V _th -V _data ), after the jump, the potential of point A V _A =V _th -V _data +V _{oled_in} , this process is a transient process, and the equal pressure jump is completed instantly, and at the same time it enters the luminous stage. Vdd charges the electroluminescence unit L along T1→DT.

In practical applications, in order to increase the voltage at point A (the voltage at point A needs to be higher than V _th during the light-emitting phase), the voltage applied to the Data line should be lower than V _{oled_in} during the discharge phase.

At this stage, on the one hand, the conduction of T5 leads to a voltage jump at point A (in order to maintain the voltage difference across the capacitor C), so that the voltage at point A rises, so that DT is turned on and utilizes the operating voltage line V _dd The provided operating voltage supplies current to the OLED, causing the OLED to emit light. On the other hand, the voltage after point A jumps becomes a voltage related to the data voltage, thus ensuring that the electroluminescent element L can emit light correctly.

From the TFT saturation current formula can be obtained:

I _L ＝K(V _GS -V _th ) ² ＝K(V _th -V _data +V _{oled_in} -V _th ) ²

=K·(V _{oled_in} -V _data ) ²

It can be seen from the above formula that the working current flowing through the electroluminescent unit at this time is not affected by the threshold voltage of the driving transistor, but only related to the data voltage V _data at this time. It completely solves the problem of the threshold voltage (V _th ) drift of the driving TFT due to the process and long-term operation, eliminates its influence on the current flowing through the electroluminescent unit, and ensures the normal operation of the electroluminescent unit.

Based on the same idea, the present invention also provides a display device, comprising any one of the above pixel circuits.

The display device here can be: electronic paper, mobile phone, tablet computer, TV, monitor, notebook computer, digital photo frame, navigator and any other product or component with display function.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, some improvements and modifications can also be made. These improvements and modifications It should also be regarded as the protection scope of the present invention.

Claims (9)

1. A pixel circuit, characterized by comprising: a first switch unit, a second switch unit, a third switch unit, a fourth switch unit, a fifth switch unit, a drive unit, an energy storage unit, and an electroluminescence unit; The first terminal of the energy storage unit is connected to the control terminal of the driving unit, which is used to pull up the voltage of the control terminal of the driving unit to make the driving unit work; the output terminal of the driving unit is connected to the anode of the electroluminescence unit, and is used to drive the electric Luminescent unit for luminescent display; The first switch unit is connected between the input terminal of the driving unit and the working voltage line, and the control terminal is connected to the second scanning signal line for providing a driving voltage to the driving unit under the control of the second scanning signal line; The second switch unit is connected between the input end of the drive unit and the first end of the energy storage unit, and the control end is connected to the first scanning signal line, for charging the energy storage unit under the control of the first scanning signal line discharge; The third switch unit is connected between the second end of the energy storage unit and the data signal line, and the control end is connected to the first scanning signal line for writing the voltage in the data signal line into the the second end of the energy storage unit; The first terminal of the fourth switch unit is connected between the output terminal of the driving unit and the anode of the electroluminescent unit, the second terminal is grounded, and the control terminal is connected to the first scanning signal line, which is used to connect the first scanning signal line to the first scanning signal line. short-circuiting the electroluminescence unit under control; The fifth switch unit is connected between the anode of the electroluminescence unit and the second terminal of the energy storage unit, and the control terminal is connected to the second scanning signal line, which is used to make the energy storage unit turn to the second scanning signal line under the control of the second scanning signal line. The electroluminescent cell discharges. 2. The pixel circuit according to claim 1, wherein each switch unit and the drive unit are thin film field effect transistors, the control terminal of each switch unit is the gate of the thin film field effect transistor, and the other two ends correspond to The source and drain of the TFT; the input end of the driving unit is the drain of the TFT, the control end is the gate of the TFT, and the output end is the source of the TFT. 3. The pixel circuit according to claim 2, wherein each thin film field effect transistor is an N-channel type. 4. The pixel circuit according to claim 1, wherein the energy storage unit is a capacitor. 5. The pixel circuit according to any one of claims 1-4, wherein the electroluminescence unit is an organic light emitting diode. 6. A driving method for a pixel circuit, characterized in that it is used to drive the pixel circuit as claimed in any one of claims 1-5, wherein each frame working period includes a charging phase, a discharging phase and a light emitting phase stage, where In the charging stage, apply a voltage to the scanning signal line to turn on all the switch units, so that the working voltage line charges the first end of the energy storage unit; In the discharge phase, applying a voltage to the scanning signal line to conduct the second switch unit, the third switch unit, and the fourth switch unit, and applying a data voltage to the data signal line to discharge the first end of the energy storage unit; In the light-emitting phase, a voltage is applied to the scanning signal line to turn on the first switch unit and the fifth switch unit, so that the electroluminescent unit emits light. 7. The method according to claim 6, wherein when each switch unit in the pixel circuit is an N-channel thin film field effect transistor, the method comprises: In the charging phase, a high-level signal is applied to both the first scanning signal line and the second scanning signal line; In the discharge phase, a high-level signal is applied to the first scanning signal line; In the light-emitting phase, a high-level signal is applied to the second scanning signal line. 8. The method according to claim 6, further comprising a voltage stabilization stage after the discharge stage and before the light-emitting stage, In the voltage stabilizing phase, a voltage is applied to the scanning signal line to turn off all switching units. 9. A display device, comprising the pixel circuit according to any one of claims 1-5.