PIXEL CIRCUIT AND PIXEL DRIVING METHOD

• US 20110090137A1
• Filed: 10/15/2010
• Published: 04/21/2011
• Est. Priority Date: 10/16/2009
• Status: Active Grant

• Current Assignee: AU Optronics Corporation
• Original Assignee: AU Optronics Corporation
• Inventors: LIU, Chun-Yen, Wu, Yuan-Chun
• Granted Patent: US 8,665,183 B2
• Time in Patent Office: Days
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

An exemplary pixel circuit includes an OLED, a storage capacitor, a driving transistor and first through fourth switching transistors. The driving transistor is for driving the OLED at a predetermined brightness. The first source/drain electrode of the driving transistor is coupled to a terminal of the storage capacitor, the second source/drain electrode is coupled to the OLED, and the gate electrode is coupled to receive a data voltage through the first switching transistor. Gate-on voltages of the first and second switching transistors are in opposite phases to each other, and the first and second switching transistors are controlled by the same control signal. Likewise, gate-on voltages of the third and fourth switching transistors are in opposite phases to each other, and the third and fourth switching transistors are controlled by the same control signal. A pixel driving method is also disclosed.

Claims

1. A pixel circuit, comprising:

an organic light emitting diode (OLED);

a storage capacitor having a first terminal and a second terminal;

a driving transistor for driving the OLED, wherein a source electrode of the driving transistor is electrically coupled to the first terminal of the storage capacitor, and a drain electrode of the driving transistor is electrically coupled to the OLED;

a first switching transistor, wherein a gate electrode of the first switching transistor is electrically coupled to a first scanning line, a source electrode of the first switching transistor is electrically coupled to the gate electrode of the driving transistor, and a drain electrode of the first switching transistor is electrically coupled to a data line;

a second switching transistor, wherein a gate electrode of the second switching transistor is electrically coupled to the first scanning line, a source electrode of the second switching transistor is electrically coupled to a first predetermined voltage, and a drain electrode of the second switching transistor is electrically coupled to the first terminal of the storage capacitor;

a third switching transistor, wherein a gate electrode of the third switching transistor is electrically coupled to a second scanning line, a source electrode of the third switching transistor is electrically coupled to a second predetermined voltage, a drain electrode of the third switching transistor is electrically coupled to the second terminal of the storage capacitor; and

a fourth switching transistor, wherein a gate electrode of the fourth switching transistor is electrically coupled to the second scanning line, a source electrode of the fourth switching transistor is electrically coupled to the gate electrode of the driving transistor, and the second source/drain electrode of the fourth switching transistor is electrically coupled to the second terminal of the storage capacitor;

wherein gate-on voltages of the first and the second switching transistors are in opposite phases, and gate-on voltages of the third and the fourth switching transistors are in opposite phases.

2. The pixel circuit as claimed in claim 1, wherein the first switching transistor is an N-channel transistor, and the second switching transistor is a P-channel transistor.

3. The pixel circuit as claimed in claim 2, wherein the third switching transistor is a P-channel transistor, and the fourth switching transistor is an N-channel transistor.

4. A pixel driving method of an active matrix organic light emitting diode (OLED) display, wherein the active matrix OLED display comprises a data line, a first pixel and a second pixel, the first pixel and the second pixel being electrically coupled to the data line, each of the first pixel and the second pixel comprising an OLED, a storage capacitor, a driving transistor and a first switching transistor, the driving transistor being used for driving the OLED, a source electrode of the driving transistor being electrically coupled to a first terminal of the storage capacitor, a drain electrode of the driving transistor being electrically coupled to the OLED, a gate electrode of the driving transistor being electrically coupled to a source electrode of the first switching transistor, a drain electrode of the first switching transistor being electrically coupled to the data line, the pixel driving method comprising the steps of:

in a resetting stage, supplying a first predetermined voltage to the first terminal of the storage capacitor, and supplying a second predetermined voltage to a second terminal of the storage capacitor;

in a writing stage, switching on the first switching transistor to allow a data voltage on the data line to be supplied to the gate electrode of the driving transistor through the first switching transistor, discharging the first terminal of the storage capacitor through the driving transistor and the OLED, and keeping the voltage of the second terminal of the storage capacitor at the second predetermined voltage; and

in a light emission stage, supplying the first predetermined voltage to the first terminal of the storage capacitor again, switching off the first switching transistor, enabling the second terminal of the storage capacitor to be electrically communicated with the gate electrode of the driving transistor, and thereby the OLED is driven by the driving transistor;

wherein the data voltage on the data line occurs a transient in a time period starting from the time of the first switching transistor of the first pixel being switched off in the writing stage to the time of the first switching transistor of the second pixel being switched on in the writing stage.

5. The pixel driving method as claimed in claim 4, wherein when each of the first pixel and the second pixel further comprises a second switching transistor and a third switching transistor, the second switching transistor being electrically coupled between the first predetermined voltage and the first terminal of the storage capacitor, the third switching transistor being electrically coupled between the second predetermined voltage and the second terminal of the storage capacitor, in the resetting stage, the step of supplying the first predetermined voltage to the first terminal of the storage capacitor and supplying the second predetermined voltage to the second terminal of the storage capacitor comprises:

switching off the first switching transistor, and switching on the second switching transistor and the third switching transistor.

6. The pixel driving method as claimed in claim 5, wherein the first and second switching transistors are controlled by the same control signal.

7. The pixel driving method as claimed in claim 5, wherein when each of the first pixel and the second pixel further comprises a fourth switching transistor electrically coupled between the second terminal of the storage capacitor and the gate electrode of the driving transistor, in the writing phase, the step of switching on the first switching transistor to allow the data voltage on the data line to be supplied to the gate electrode of the driving transistor through the first switching transistor, discharging the first terminal of the storage capacitor through the driving transistor and the OLED, and keeping the voltage of the second terminal of the storage capacitor at the second predetermined voltage comprises:

switching on the first switching transistor, switching off the second switching transistor, switching on the third switching transistor, and switching off the fourth switching transistor.

8. The pixel driving method as claimed in claim 7, wherein the third and fourth switching transistors are controlled by the same control signal.

9. The pixel driving method as claimed in claim 7, wherein in the light emission, the step of supplying the first predetermined voltage again onto the first terminal of the storage capacitor, switching off the first switching transistor, enabling the second terminal of the storage capacitor electrically communicated with the gate electrode of the driving transistor and thereby the OLED is driven by the driving transistor comprises:

switching off the first switching transistor, switching on the second switching transistor, switching off the third switching transistor and switching on the fourth switching transistor.

10. A pixel driving method of an active matrix organic light emitting diode (OLED) display, wherein the active matrix OLED display comprises a data line, a first pixel and a second pixel, the first pixel and the second pixel being electrically coupled to the data line, each of the first pixel and the second pixel comprising an OLED, a storage capacitor, a driving transistor and a first switching transistor, the driving transistor being used for driving the OLED, a source electrode of the driving transistor being electrically coupled to a first terminal of the storage capacitor, a drain electrode of the driving transistor being electrically coupled to the OLED, a gate electrode of the driving transistor being electrically coupled to a source electrode of the first switching transistor, a drain electrode of the first switching transistor being electrically coupled to the data line;

the pixel driving method being adapted for sequentially driving the first pixel and the second pixel, and during driving each of the first pixel and the second pixel comprising the steps of;

in a resetting stage, supplying a first predetermined voltage to the first terminal of the storage capacitor, and supplying a second predetermined voltage to a second terminal of the storage capacitor;

in a writing stage, enabling the data line to supply a data voltage to the gate electrode of the driving transistor through the first switching transistor, discharging the first terminal of the storage capacitor through the driving transistor and the OLED, and keeping the voltage of the second terminal of the storage capacitor at the second predetermined voltage; and

in a light emission stage, supplying the first predetermined voltage again to the first terminal of the storage capacitor, switching off the first switching transistor, enabling the second terminal of the storage capacitor to be electrically communicated with the gate electrode of the driving transistor, and thereby the OLED is driven by the driving transistor;

wherein during driving the second pixel, the pixel driving method further comprises the steps of;

in the writhing stage, before enabling the data line to supply the data voltage to the gate electrode of the driving transistor through the first switching transistor, enabling the data line to supply a precharge voltage to the gate electrode of the driving transistor through the first switching transistor, wherein the precharge voltage is supplied on the data line in a time period starting from the time of the first switching transistor of the first pixel being switched off in the writing stage to the time of the first switching transistor of the second pixel being switched on in the writing stage, and the precharge voltage is larger than the sum of the data voltage on the gate electrode of the driving transistor of the second pixel and the threshold voltage of the driving transistor of the second pixel.

11. The pixel driving method as claimed in claim 10, wherein when each of the first pixel and the second pixel further comprises a second switching transistor and a third switching transistor, the second switching transistor being electrically coupled between the first predetermined voltage and the first terminal of the storage capacitor, the third switching transistor being electrically coupled between the second predetermined voltage and the second terminal of the storage capacitor, in the resetting stage, the step of supplying the first predetermined voltage to the first terminal of the storage capacitor and supplying the second predetermined voltage to the second terminal of the storage capacitor comprises:

switching off the first switching transistor, and switching on the second switching transistor and the third switching transistor.

12. The pixel driving method as claimed in claim 11, wherein the first and second switching transistors are controlled by the same control signal.

13. The pixel driving method as claimed in claim 11, wherein when each of the first pixel and the second pixel further comprises a fourth switching transistor electrically coupled between the second terminal of the storage capacitor and the gate electrode of the driving transistor, in the writing stage, the step of enabling the data line to supply the data voltage to the gate electrode of the driving transistor through the first switching transistor, discharging the first terminal of the storage capacitor through the driving transistor and the OLED, and keeping the voltage of the second terminal of the storage capacitor at the second predetermined voltage comprises:

switching on the first switching transistor, switching off the second switching transistor, switching on the third switching transistor, and switching off the fourth switching transistor.

14. The pixel driving method as claimed in claim 13, wherein the third and fourth switching transistors are controlled by the same control signal.

15. The pixel driving method as claimed in claim 13, wherein in the light emission stage, the step of supplying the first predetermined voltage again to the first terminal of the storage capacitor, switching off the first switching transistor, enabling the second terminal of the storage capacitor to be electrically communicated with the gate electrode of the driving transistor, and thereby the OLED is driven by the driving transistor comprises:

switching off the first switching transistor, switching on the second switching transistor, switching off the third switching transistor and switching on the fourth switching transistor.

16. The pixel driving method as claimed in claim 10, wherein when the active matrix OLED display further comprises a demultiplexer, and the data line is electrically coupled to an output terminal of the demultiplexer, during driving the second pixel, the pixel driving method further comprises steps of:

enabling the demultiplexer and thereby the precharge voltage is supplied to the data line through the demultiplexer; and

enabling the demultiplexer again and thereby the precharge voltage of the data line is changed to be the data voltage.