PIXEL CIRCUIT, DRIVING METHOD THEREOF, AND DISPLAY DEVICE

• US 20140175992A1
• Filed: 12/18/2013
• Published: 06/26/2014
• Est. Priority Date: 12/21/2012
• Status: Active Grant

• Current Assignee: Beijing BOE Optoelectronics Technology Co Ltd. (BOE Technology Group Co., Ltd.)
• Original Assignee: Beijing BOE Optoelectronics Technology Co Ltd. (BOE Technology Group Co., Ltd.)
• Inventors: YANG, Shengji
• Granted Patent: US 9,483,979 B2
• Time in Patent Office: Days
• US Class Current: 315/172
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0861 with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2310/0262 The addressing of the pixel, in a display other than an active matrix LCD, involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependent on signals of two data electrodes
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

Provided are a pixel circuit, a driving method thereof, and a display device, which relate to the field of the display technology and can effectively compensate variation in currents due to ununiformity and drift of threshold voltages of driving Thin Film Transistors as well as ununiformity of OLEDs. The pixel circuit comprises: a light-emitting element; a driving TFT; a first TFT having a drain connected to a gate of the driving TFT; a second TFT having a drain connected to a source of the driving TFT; a third TFT having a source connected to a drain of the driving TFT, and a drain connected to the light-emitting element; a fourth TFT having a source connected to the gate of the driving TFT, and a drain connected to the drain of the driving TFT; a fifth TFT having a drain connected to the source of the driving TFT; and a capacitor.

Claims

1. A pixel circuit comprising:

a light-emitting element;

a driving Thin Film Transistor TFT for driving the light-emitting element;

a first TFT having a source connected to a reference voltage terminal, a drain connected to a gate of the driving TFT, and a gate for receiving a first control signal;

a second TFT having a gate for receiving a first scan signal, a drain connected to a source of the driving TFT, and a source for receiving a data voltage signal;

a third TFT having a gate for receiving a second scan signal, a source connected to a drain of the driving TFT, and a drain connected to the light-emitting element;

a fourth TFT having a gate for receiving the first scan signal, a source connected to the gate of the driving TFT, and a drain connected to the drain of the driving TFT;

a fifth TFT having a gate for receiving the second scan signal, a source connected to a power supply voltage terminal, and a drain connected to the source of the driving TFT;

a capacitor having one terminal connected to a first node A, and the other terminal connected to a second node B, wherein the first node A is a connection point where the drain of the first TFT is connected to the gate of the driving TFT, and the second node B is connected to the reference voltage terminal.

2. The pixel circuit of claim 1, wherein the first TFT, the second TFT, the third TFT, the fourth TFT, and the fifth TFT and the driving TFT are all P type Thin Film Transistors.

3. The pixel circuit of claim 2, wherein the power supply voltage terminal supplies a positive power supply voltage, the positive power supply voltage is higher than a reference voltage at the reference voltage terminal, and a data voltage of the data voltage signal is lower than the positive power supply voltage.

4. The pixel circuit of claim 2, wherein an anode of the light-emitting element is connected to the drain of the third TFT, and a cathode of the light-emitting element is connected to the reference voltage terminal.

5. A display device having the pixel circuit of claim 1 arranged therein.

6. The display device of claim 5, wherein the first TFT, the second TFT, the third TFT, the fourth TFT, and the fifth TFT and the driving TFT are all P type Thin Film Transistors;

the power supply voltage terminal supplies a positive power supply voltage, the positive power supply voltage is higher than a reference voltage at the reference voltage terminal, and a data voltage of the data voltage signal is lower than the positive power supply voltage.

7. The display device of claim 6, wherein, in the pixel unit, an anode of the light-emitting element is connected to the drain of the third TFT, and a cathode of the light-emitting element is connected to the reference voltage terminal.

8. A driving method applicable to the pixel circuit of claim 1, comprising:

in a resetting phase, turning on the first TFT under a control of a first control signal, discharging electric charges stored at the first node via the first TFT, resetting a voltage signal at the gate of the driving TFT so as turn on the driving TFT, and turning off the second TFT, the third TFT, the fourth TFT and the fifth TFT;

in a compensating phase, turning on the second TFT and the fourth TFT under a control of a first scan signal, making the driving TFT continue to be turned on, wherein since the fourth TFT is turned on, the gate and the drain of the driving TFT are connected electrically;

charging the first node by a data signal via the driving TFT, so that a voltage at the node rises; and

turning off the first TFT, the third TFT and the fifth TFT; and

in a maintaining light-emission phase, turning on the third TFT and the fifth TFT under a control of a second scan signal, keeping the voltage at the gate of the driving TFT unchanged by the capacitor, and making the driving TFT continue to be turned on, and driving the OLED to emit light by a power supply voltage; and

turning off the first TFT, the second TFT and the fourth TFT.

9. The driving method of claim 8, wherein the first TFT, the second TFT, the third TFT, the fourth TFT, and the fifth TFT and the driving TFT are all P type Thin Film Transistors;

the power supply voltage terminal supplies a positive power supply voltage, the positive power supply voltage is higher than a reference voltage at the reference voltage terminal, and a data voltage of the data voltage signal is lower than the positive power supply voltage.

10. The driving method of claim 9, wherein, in the pixel circuit, an anode of the light-emitting element is connected to the drain of the third TFT, and a cathode of the light-emitting element is connected to the reference voltage terminal.