ORGANIC LIGHT EMITTING DIODE DISPLAY AND PIXEL DRIVING METHOD THEREOF

Abstract

A light emitting diode (OLED) display and pixel driving method thereof are disclosed. Each storage capacitor is discharged via the driving TFT and OLED until conductive current of each OLED is almost zero so as to record a sum of a voltage drop across each OLED under a specific condition and the threshold voltage of the driving TFT. By using the sum of the voltage drop across each OLED and the threshold voltage of the corresponding TFT in the subsequent OLED driving process, the luminance reduction issue caused by TFT threshold-voltage shift and OLED material decay can be solved.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a conventional pixel circuit.

FIG. 2 is a characteristic diagram of the OLED in FIG. 1.

FIG. 3 is a flow chart of the method for driving OLED pixels according to the invention.

FIG. 4 is a schematic diagram of an OLED display according to a preferred embodiment of the invention.

FIG. 5 is a timing diagram of the pixel driving method according to the invention.

Claims

1. A method for driving a pixel, the pixel having an organic light emitting diode (OLED), a storage capacitor, and a thin film transistor (TFT), the TFT having a first terminal, a second terminal, and a gate, the first terminal electrically being coupled to one end of the OLED, the other end of the OLED being adapted for receiving a first voltage, the second terminal being adapted for receiving a second voltage, the gate of the TFT being electrically coupled to an end of the storage capacitor, the method comprising: providing the second voltage to the end of the storage capacitor;providing a pixel voltage to the other end of the storage capacitor;discharging the storage capacitor via the TFT and the OLED until conductive current of the OLED is substantially zero and the storage capacitor stores an amount of charges; andgenerating a pixel current by the TFT for driving the OLED to emit light according to the amount of charges stored in the storage capacitor.

2. The method according to claim 1, wherein: the pixel comprises a first switch, a second switch and a third switch,the first switch is coupled between the second voltage and the second terminal of the TFT,the second switch is coupled between the second terminal and the gate of the TFT,the third switch is coupled between the pixel voltage and the other end of the storage capacitor, andproviding the second voltage and the pixel voltage to the storage capacitor further comprises:switching on the first switch, the second switch and the third switch such that a terminal voltage at the end of the storage capacitor is the second voltage and a terminal voltage at the other end of the storage capacitor is the pixel voltage.

3. The method according to claim 2, wherein discharging the storage via the TFT and OLED further comprises: switching off the first switch and switching on the second switch and the third switch such that the storage capacitor is discharged via the TFT and the OLED.

4. The method according to claim 3, further comprising: switching off the first switch, the second switch and the third switch after the storage capacitor is discharged via the TFT and the OLED.

5. The method according to claim 4, wherein the pixel further comprises a fourth switch coupled between the gate and the first terminal of the TFT, and generating a pixel current by the TFT for driving the OLED to emit light according to the amount of charges of the storage capacitor comprises: switching on the first switch and the fourth switch and switching off the second switch and the third switch such that the TFT drives the OLED to emit light according to the amount of charges of the storage capacitor.

6. An organic light emitting diode (OLED) pixel circuit, comprising: a storage capacitor;an organic light emitting diode (OLED) having a first end and a second end, wherein the second end of the OLED is coupled to a first voltage;a first thin film transistor (TFT) for driving the OLED to emit light, the first TFT having a gate electrically coupled to one end of the storage capacitor, and a first terminal electrically coupled to a first end of the OLED,a second TFT having a gate for receiving a first scan signal, a first terminal for receiving a second voltage, and a second terminal electrically coupled to a second terminal of the first TFT;a third TFT for discharging the storage capacitor via the first TFT and the OLED, the third TFT having a gate for receiving a second scan signal, and a first terminal and a second terminal respectively coupled to the second terminal and the gate of the first TFT;a fourth TFT having a gate for receiving the scan signal, a first terminal electrically coupled to the other end of the storage capacitor, and a second terminal for receiving a pixel voltage; anda fifth TFT having a gate for receiving the first scan signal, a first terminal electrically coupled to the first terminal of the first TFT, and a second terminal electrically coupled to the other end of the storage capacitor;wherein the first voltage is smaller than the second voltage.

7. A display incorporating the pixel circuit according to claim 6.

8. A light emitting diode (OLED) display, comprising: a driving circuit for outputting a pixel voltage, a first scan signal, and a second scan signal;a pixel circuit, comprising: an OLED having a first end and a second end, wherein the second end of the OLED is coupled to a first voltage;a storage capacitor;a first TFT for driving the OLED to emit light, the first TFT having a gate electrically coupled to one end of the storage capacitor, and a first terminal electrically coupled to the first end of the OLED;a second TFT having a gate for receiving the first scan signal, a first terminal for receiving a second voltage, and a second terminal electrically coupled to a second terminal of the first TFT;a third TFT for discharging the storage capacitor via the first TFT and the OLED, the third TFT having a gate for receiving the second scan signal, and a first terminal and a second terminal coupled to the second terminal and the gate of the first TFT, respectively;a fourth TFT having a gate for receiving the second scan signal, a first terminal electrically coupled to the other end of the storage capacitor, and a second terminal for receiving a pixel voltage; anda fifth TFT having a gate for receiving the first scan signal, a first terminal electrically coupled to the first terminal of the first TFT, and a second terminal electrically coupled to the other end of the storage capacitor.

9. The OLED display according to claim 8, wherein when driving the pixel, the driving circuit switches on the second TFT, the third TFT, the fourth TFT and the fifth TFT via the first scan signal and the second scan signal such that a terminal voltage at the end of the storage capacitor is the second voltage and a terminal voltage at the other end of the storage capacitor is the pixel voltage, and then the driving circuit switches off the second TFT and the fifth TFT via the first scan signal and the second scan signal and continuously switches on the third TFT and the fourth TFT such that the storage capacitor is discharged via the first TFT and the OLED, and then the driving circuit switches on the second TFT and the fifth TFT and switches off the third TFT and the fourth TFT such that the first transistor generates a pixel current for driving the OLED to emit light according to an amount of charges of the storage capacitor.