WO2015196730A1

WO2015196730A1 - Pixel circuit, driving method therefor and display device

Info

Publication number: WO2015196730A1
Application number: PCT/CN2014/092536
Authority: WO
Inventors: 杨盛际; 董学; 王海生; 丁小梁; 刘英明; 赵卫杰; 任涛
Original assignee: 京东方科技集团股份有限公司; 北京京东方光电科技有限公司
Priority date: 2014-06-23
Filing date: 2014-11-28
Publication date: 2015-12-30
Also published as: CN104167168A; CN104167168B

Abstract

A pixel circuit, a driving method therefor and a display device. The pixel circuit comprises: a first switch unit (T1), a second switch unit (T2), a third switch unit (T3), a fourth switch unit (T4), a fifth switch unit (T5), a drive unit (DT), an energy storage unit (C) and an electroluminescent unit (L). Control ends of the first switch unit (T1) and the fifth switch unit (T5) are connected to a second scanning signal line (Scan[2]), and control ends of the second switch unit (T2), the third switch unit (T3) and the fourth switch unit (T4) are connected to a first scanning signal line (Scan[1]). The pixel circuit solves the problem of uneven display brightness caused by drifting of the threshold voltage of a drive transistor (DT). In addition, since the pixel circuit is only provided with two switch signal input lines, not only is energy consumption saved, but interference between the lines is also reduced.

Description

Pixel circuit, driving method thereof and display device

Technical field

The present disclosure relates to a pixel circuit, a driving method thereof, and a display device.

Background technique

Organic light-emitting display (OLED) is one of the hotspots in the research field of flat panel displays. Compared with liquid crystal displays, OLEDs have the advantages of low energy consumption, low production cost, self-illumination, wide viewing angle and fast response. At present, OLEDs have begun to replace traditional liquid crystal (LCD) displays in display fields such as mobile phones, PDAs, and digital cameras. Pixel driver circuit design is the core technology 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, OLEDs are current-driven and require a constant current to control illumination.

Due to process process and device aging, etc., in the original 2T1C driver circuit (including two thin film field effect transistors and one capacitor), the threshold voltage of the driving TFT of each pixel has unevenness, which leads to the flow of each The current of the pixel OLED changes to make the display brightness uneven, thereby affecting the display effect of the entire image.

Summary of the invention

The present disclosure addresses the problem of display device display unevenness in brightness, and reduces the number of signal lines for the pixel circuit in the display device, reduces the cost of the integrated circuit, and increases the pixel density of the display device.

The present disclosure provides a pixel circuit including a first switching unit, a second switching unit, a third switching unit, a fourth switching unit, a fifth switching unit, a driving unit, an energy storage unit, and an electroluminescent unit;

The first end of the energy storage unit is connected to the control end of the driving unit for pulling the voltage of the control end of the driving unit to operate the driving unit; the input end of the driving unit is connected to the anode of the electroluminescent unit for driving the electric The illuminating unit performs illuminating display;

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

The second switching unit is connected between the input end of the driving unit and the first end of the energy storage unit, and is controlled The end is connected to the first scan signal line for charging and discharging the energy storage unit under the control of the first scan signal line;

The third switching 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 under the control of the first scanning signal line a second end of the energy storage unit;

a first end of the fourth switching unit is connected between the output end of the driving unit and the anode of the electroluminescent unit, the second end is grounded, and the control end is connected to the first scanning signal line for the first scanning signal line Short-circuiting the electroluminescent unit under control;

a fifth switching unit is connected between the anode of the electroluminescent unit and the second end of the energy storage unit, and the control end is connected to the second scanning signal line for enabling the energy storage unit under the control of the second scanning signal line The electroluminescent unit is discharged.

Alternatively, each of the switching units and the driving unit is a thin film field effect transistor, and the control terminals of the respective switching units are gates, the other ends correspond to the source and the drain; and the input ends of the driving units are drains. The control terminal is the gate and the output terminal is the source.

Alternatively, each of the thin film field effect transistors is of an N-channel type.

Alternatively, the energy storage unit is a capacitor.

Alternatively, the electroluminescent unit is an organic light emitting diode.

The present disclosure further provides a driving method of a pixel circuit for driving the pixel circuit according to any one of the above, wherein each frame operating period includes a charging phase, a discharging phase, and a lighting phase, wherein

In the charging phase, a voltage is applied to the scanning signal line to turn on all of the switching units to charge the working voltage line to the first end of the energy storage unit;

In the discharging phase, a voltage is applied to the scanning signal line to turn on the second switching unit, the third switching unit, and the fourth switching unit, and a data voltage is applied 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 switching unit and the fifth switching unit to cause the electroluminescent unit to emit light.

Alternatively, when each of the switching units 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 scan signal line and the second scan signal line;

In the discharging 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 scan signal line.

Alternatively, a voltage stabilization phase is included after the discharge phase and before the illumination phase,

During the regulation phase, a voltage is applied across the scan signal lines to turn off all switching units.

The present disclosure also provides a display device comprising the pixel circuit of any of the above.

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

DRAWINGS

FIG. 1 is a schematic structural diagram of a pixel circuit according to an embodiment of the present disclosure;

2 is a timing diagram of key signals in a pixel circuit according to an embodiment of the present disclosure;

3a-3c are schematic diagrams of current flow and voltage values of pixel circuits at different timings in an embodiment of the present disclosure.

detailed description

The specific embodiments of the present disclosure are further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present disclosure, and are not intended to limit the scope of the disclosure.

FIG. 1 schematically shows the structure of a pixel circuit of an embodiment of the present disclosure. As shown in FIG. 1, the pixel circuit includes:

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 both connected to the second scan signal line [2]; the first end of T1 is connected to the working voltage line V _dd , and the second end is connected to the input end of the driving unit DT; the first end of T5 Connected to the output of the DT, the second end of which is connected to the second end B of the energy storage unit C.

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

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

It can be understood that, in the embodiment of the present disclosure, the control terminal is connected to the plurality of switch units of the same scan signal line (the three switch units T2, T3, and T4 connected to the Scan[1] are connected to the Scan[2]. The two switching units T1 and T5) should be switches of the same channel type, that is, both of them are turned on at the same level or are turned on at the same level, thereby ensuring the conduction of the two switching units connected to the same scanning signal line. Or the shutdown state is the same.

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

Alternatively, each of the switching unit and the driving unit is a thin film field effect transistor TFT, and the control terminals of the respective switching units are gates, the first ends of the respective switching units are the drains of the TFTs, and the second ends of the respective switching units are TFTs. 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 switching unit and the driving unit can also be other suitable devices or device combinations.

It is not difficult to understand that the transistors corresponding to the driving unit and the switching unit herein may be transistors in which the source and the drain are interchangeable, or the first end of each of the switching units and the driving unit may be the drain of the transistor according to the type of conduction. The second end is the source of the transistor, and those skilled in the art can obtain the reverse connection of the source and the drain of each transistor in the pixel circuit provided by the present disclosure without any creative labor, and can obtain the information provided by the present disclosure. The circuit structures of the same or similar technical effects that can be achieved by the technical solutions should also fall within the protection scope of the present disclosure.

Further, in the embodiments of the present disclosure, all of the thin film field effect transistors may be of an N-channel type. Using the same type of transistor, the process can be unified to improve the yield of the product. Those skilled in the art can understand that in practical applications, the types of transistors 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. The technical solution provided by the present application can be realized as long as the on/off states of the two switching units connected to the same scanning signal line can be made the same.

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

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

3a-3c schematically illustrate the power of pixel circuits in different embodiments at different timings in embodiments of the present disclosure Flow direction and voltage value. FIG. 2 is a timing diagram showing key signals in a pixel circuit provided by an embodiment of the present disclosure. A method of driving a pixel circuit provided in an alternative embodiment of the present disclosure will be described in detail below with reference to FIGS. 2 and 3a-3c. As shown in FIG. 2, the timing chart of the scan signals input to the respective scan signal lines when the pixel circuit provided by the present disclosure is operated can be divided into four stages, which are respectively represented as a reset stage W1, a discharge stage W2, and a stable state in FIG. Pressing stage W3, lighting stage W4. In each stage, the current flow and voltage values of the pixel circuit are as shown in Figures 3a, 3b, and 3c, respectively. For convenience of explanation, it is assumed that each of the switching units is an N-channel type TFT.

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

The purpose of this phase is to reset the voltage at point A and maintain the voltage at point A at a higher potential, allowing the voltage at point A to become a lower reasonable by appropriate control in subsequent processes. Potential. Since this process is mainly for resetting 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 FIG. 2, Scan[1] is at a high level, Scan[2] is at a low level, and V _{data is} continuously applied to the data signal line Data, at which time T2, T3, and T4 are guided. Pass, T1, T5 are disconnected. As shown in Figure 3b, capacitor C discharges along T2-DT-T4 and is discharged until the voltage drop is _Vth . That is, after the end of the discharge, the potential at point A drops to V _th , and the potential at point B remains V _data , where V _th is the threshold voltage of DT. The purpose of this phase is to change the voltage at point A to a voltage associated with the threshold voltage _{Vth of} DT, thereby being able to cancel the threshold voltage _Vth of DT during the subsequent illumination phase, eliminating the drift of the threshold voltage _Vth. The effect of the current of the electroluminescent unit. In addition, in this stage, the voltage at point B is set to the data voltage _Vdata , and the current flowing through the electroluminescent element L is affected in the final light-emitting stage, so that the electroluminescence element L corresponds to the light emission, so this stage It is actually 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 low, and all TFTs are turned off. This process time is relatively short, mainly for the purpose of stabilizing the pressure difference (V _th -V _data ) between point A and point B after sufficient discharge in the discharge phase W2. Those skilled in the art will appreciate, the process is better to make the difference of pressure between point A and point B is V _th -V _data. Even in the absence of this stage, the technical solutions provided by the present disclosure can be implemented as well.

In the lighting phase W4, Scan[1] is low and Scan[2] is high. 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 conduction voltage of the electroluminescent unit L. After the conduction of T5, the voltage at the B terminal of the capacitor C is consistent with the anode voltage of L, that is, For V _{oled_in} ). Since the A terminal floats, V _A and V _B achieve voltage equal hopping (maintaining the original differential pressure V _th -V _data ). After the jump, the potential of point A is V _A = V _th -V _data +V _{oled_in} . This process is a transient process, the isostatic jump is completed instantaneously, and at the same time enters the illumination phase. Vdd charges the electroluminescent unit L along T1 → DT.

In practice, in order to increase the voltage at point A (voltage at point A is higher than the required emission phase V _th), the discharge phase, the voltage applied to the Data line should be less than _V oled_in.

In this phase, on the one hand, the conduction of T5 causes a voltage jump at point A (in order to maintain the voltage difference across capacitor C), causing the voltage at point A to rise, thereby turning DT on and using the operating voltage line V. The operating voltage provided by _dd supplies current to the OLED such that the OLED emits light. On the other hand, the voltage after the point A jump becomes a voltage associated with the data voltage, thereby ensuring that the electroluminescent element L can emit light correctly.

The TFT saturation current formula can be obtained:

IL=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 operating 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. In this way, the problem that the threshold voltage (V _th ) of the driving TFT is drifted due to the process process and long-time operation is completely solved, the influence of the current flowing through the electroluminescent unit is eliminated, and the normal operation of the electroluminescent unit is ensured.

Based on the same concept, an embodiment of the present disclosure further provides a display device including any of the above pixel circuits.

The display device here can be: electronic paper, mobile phone, tablet computer, television, display, notebook computer, digital photo frame, navigator and the like with any display product or component.

The above description is only an exemplary embodiment of the present disclosure. It should be noted that a number of modifications and refinements may be made by those skilled in the art without departing from the principles of the present disclosure, and such improvements and modifications are also considered to be within the scope of the present disclosure.

The present application claims the priority of the Chinese Patent Application No. 201410283800.9 filed on Jun. 23, 2014, the content of

Claims

A pixel circuit comprising: a first switching unit, a second switching unit, a third switching unit, a fourth switching unit, a fifth switching unit, a driving unit, an energy storage unit and an electroluminescent unit;

The first end of the energy storage unit is connected to the control end of the driving unit for pulling the voltage of the control end of the driving unit to operate the driving unit; the input end of the driving unit is connected to the anode of the electroluminescent unit for driving the electric The illuminating unit performs illuminating display;

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

The second switching unit is connected between the input end of the driving 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 switching 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 under the control of the first scanning signal line a second end of the energy storage unit;

a first end of the fourth switching unit is connected between the output end of the driving unit and the anode of the electroluminescent unit, the second end is grounded, and the control end is connected to the first scanning signal line for the first scanning signal line Short-circuiting the electroluminescent unit under control;

a fifth switching unit is connected between the anode of the electroluminescent unit and the second end of the energy storage unit, and the control end is connected to the second scanning signal line for enabling the energy storage unit under the control of the second scanning signal line The electroluminescent unit is discharged.
The pixel circuit according to claim 1, wherein each of the switching units and the driving unit is a thin film field effect transistor, and the control end of each switching unit is a gate of a thin film field effect transistor, and the other ends respectively correspond to a thin film field effect The source and the drain of the transistor; the input end of the driving unit is the drain of the thin film field effect transistor, the control end is the gate of the thin film field effect transistor, and the output end is the source of the thin film field effect transistor.
The pixel circuit according to claim 2, wherein each of the thin film field effect transistors is of an N-channel type.
The pixel circuit of claim 1 wherein said energy storage unit is a capacitor.
The pixel circuit according to any one of claims 1 to 4, wherein the electroluminescent unit is an organic light emitting diode.
A driving method of a pixel circuit for driving a pixel circuit according to any one of claims 1 to 5, wherein each frame operating period includes a charging phase, a discharging phase, and a lighting phase, wherein

In the charging phase, a voltage is applied to the scanning signal line to turn on all of the switching units to charge the working voltage line to the first end of the energy storage unit;

In the discharging phase, a voltage is applied to the scanning signal line to turn on the second switching unit, the third switching unit, and the fourth switching unit, and a data voltage is applied 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 switching unit and the fifth switching unit to cause the electroluminescent unit to emit light.
The method of claim 6, wherein when each of the switching units 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 scan signal line and the second scan signal line;

In the discharging 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 scan signal line.
The method of claim 6 further comprising a voltage stabilization phase after the discharge phase and before the illumination phase,

In the regulation phase, a voltage is applied across the scan signal lines to turn off all of the switching units.
A display device comprising the pixel circuit of any of claims 1-5.