Pixel with reverse bias power source and organic light emitting device using the same

• US 9,035,858 B2
• Filed: 08/10/2011
• Issued: 05/19/2015
• Est. Priority Date: 12/28/2010
• Status: Active Grant

• Current Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Inventors: Kim, Do-Ik, Jeong, Joo-Hyeon
• Primary Examiner(s): Pappas, Claire X
• Assistant Examiner(s): STONE, ROBERT M
• Application Number:
  US13/207,369
• Publication Number:
  US 20120162176A1
• Time in Patent Office: 1,378 Days
• Field of Search: 345/82
• US Class Current: 345/82
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2320/0214 with crosstalk due to leakage current of pixel switch in active matrix panels
• CPC Class Codes: G09G 2320/0238 Improving the black level
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element

Abstract

A pixel and an organic light emitting diode (OLED) display device including the same are disclosed. The pixel includes an organic light emitting diode and an inverse voltage transistor positioned between an anode of the organic light emitting diode and a reverse bias power source, and configured to transmit the inverse voltage to the organic light emitting diode (OLED).

Claims

1. A pixel comprising:

a pixel driver formed near an intersection of a scan line and a data line, wherein the pixel driver is connected to a first power source voltage supply line, and comprises;

a driving transistor configured to transmit a driving current according to a data voltage corresponding to a data signal from the data line, wherein the data voltage is applied to the driving transistor according to a scan signal transmitted from the scan line;

an organic light emitting diode (OLED) configured to emit light according to the driving current; and

an inverse voltage transistor positioned between an anode of the organic light emitting diode (OLED) and a reverse bias power source, the inverse voltage transistor including a gate electrode connected to one of a first electrode and a second electrode, and configured to transmit an inverse voltage to the organic light emitting diode (OLED) during a turn-off period of the driving transistor, wherein a channel width to length ratio of the inverse voltage transistor is less than a channel width to length ratio of the driving transistor.

2. The pixel of claim 1, wherein the first electrode is a source electrode and the second electrode is a drain electrode, and wherein the gate electrode is connected to the source electrode.

3. The pixel of claim 2, wherein the inverse voltage transistor is a PMOS transistor, and the inverse voltage is applied to the drain electrode.

4. The pixel of claim 2, wherein the inverse voltage transistor is a NMOS transistor, and the inverse voltage is applied to the source electrode.

5. The pixel of claim 2, wherein a first current that may flow to the inverse voltage transistor is based at least in part on a shifted threshold voltage and a ratio of a width and a length of a channel of the inverse voltage transistor.

6. The pixel of claim 5 wherein the first current is greater than a leakage current of the driving transistor during the turn-off period of the driving transistor.

7. The pixel of claim 1, wherein the first electrode is a source electrode, the second electrode is a drain electrode, and the gate electrode is diode-connected to the drain electrode.

8. The pixel of claim 7, wherein the inverse voltage transistor is a PMOS transistor and the drain electrode is applied with the inverse voltage.

9. The pixel of claim 7, wherein the inverse voltage transistor is an NMOS transistor and the source electrode is applied with the inverse voltage.

10. The pixel of claim 7, wherein a first current that may flow in the inverse voltage transistor is based at least in part on the mobility of the inverse voltage transistor, a ratio of a width and a length of the channel of the inverse voltage transistor, and a voltage difference between a drain electrode and a source electrode of the inverse voltage transistor.

11. The pixel of claim 10, wherein the first current is larger than the leakage current of the driving transistor during the turn-off period of the driving transistor.

12. The pixel of claim 1, wherein the pixel driver includes:

a switching transistor transmitting a data signal from the data line to a first node when turned on in response to the scan signal transmitted from the scan line;

a capacitor including first and second electrodes respectively connected to the first node and the first power source voltage supply line and configured to store a voltage according to a difference between the data voltage according to the data signal applied to the first node and a first power source voltage; and

a driving transistor connected between the first power source voltage supply line and a second power source voltage supply line and generating a driving current corresponding to the voltage stored by the capacitor.

13. An organic light emitting diode (OLED) display device comprising:

a scan driver transmitting a plurality of scan signals to a plurality of scan lines;

a data driver transmitting a plurality of data signals to a plurality of data lines;

a controller controlling the scan driver and the data driver, and generating and supplying an image data signal corresponding to a video signal to the data driver;

a display unit including a plurality of pixels respectively connected to a corresponding scan line of a plurality of scan lines and a corresponding data line of a plurality of data lines, wherein the plurality of pixels emit light according to the image data signal; and

a power source supply supplying a first power source voltage, a second power source voltage, and an inverse voltage to the plurality of pixels,

wherein the plurality of pixels respectively include;

a driving transistor configured to transmit a driving current according to a data voltage corresponding to the data signal transmitted from the data line;

an organic light emitting diode (OLED) configured to emit light according to the driving current; and

an inverse voltage transistor positioned between an anode of the organic light emitting diode (OLED) and a reverse bias power source, the inverse voltage transistor including a gate electrode connected to one of a first electrode and a second electrode, and configured to transmit the inverse voltage to the organic light emitting diode (OLED), wherein a channel width to length ratio of the inverse voltage transistor is less than a channel width to length ratio of the driving transistor.

14. The organic light emitting diode (OLED) display device of claim 13, wherein the inverse voltage transistor includes:

the first electrode and the second electrode that are respectively a source electrode and a drain electrode, wherein the gate electrode is connected to the source electrode.

15. The organic light emitting diode (OLED) display device of claim 14, wherein the inverse voltage transistor is a PMOS transistor, and the inverse voltage is applied to the drain electrode.

16. The organic light emitting diode (OLED) display device of claim 14, wherein the inverse voltage transistor is an NMOS transistor, and the inverse voltage is applied to the source electrode.

17. The organic light emitting diode (OLED) display device of claim 13, wherein the inverse voltage transistor includes:

the first electrode and the second electrode that are respectively a source electrode and a drain electrode, and the gate electrode is diode-connected to the drain electrode.

18. The organic light emitting diode (OLED) display device of claim 17, wherein the inverse voltage transistor is a PMOS transistor, and the drain electrode is applied with the inverse voltage.

19. The organic light emitting diode (OLED) display device of claim 17, wherein the inverse voltage transistor is an NMOS transistor, and the source electrode is applied with the inverse voltage.