PIXEL CIRCUIT, ORGANIC ELECTRO-LUMINESCENT DISPLAY APPARATUS, AND METHOD OF DRIVING THE SAME

• US 20110164071A1
• Filed: 09/23/2010
• Published: 07/07/2011
• Est. Priority Date: 01/04/2010
• Status: Active Grant

• Current Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Inventors: Chung, Bo-Yong, Park, Yong-Sung
• Granted Patent: US 8,913,090 B2
• Time in Patent Office: Days
• US Class Current: 345/690
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• 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 3/3208 organic, e.g. using organic light-emitting diodes [OLED]
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3266 Details of drivers for scan electrodes
• CPC Class Codes: H05B 45/60 Circuit arrangements for operating LEDs comprising organic material, e.g. for operating organic light-emitting diodes [OLED] or polymer light-emitting diodes [PLED]
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A pixel circuit includes a light emitting device, an N-type driving transistor for outputting a driving current according to a voltage applied to the gate electrode, a first capacitor coupled to a gate electrode of the driving transistor, a second capacitor including a first terminal coupled to the gate electrode of the driving transistor and a second terminal coupled to the first electrode of the light emitting device, and second through sixth N-type transistors. An initialization period is reduced for a driving operation and the threshold voltage compensation time of a driving transistor is controlled.

Claims

1. A pixel circuit comprising:

a light emitting device comprising a first electrode and a second electrode;

a driving transistor comprising;

a first electrode;

a second electrode; and

a gate electrode, the driving transistor for outputting a driving current according to a voltage applied to the gate electrode of the driving transistor;

a first capacitor comprising a first terminal and a second terminal, the second terminal of the first capacitor being coupled to the gate electrode of the driving transistor;

a second capacitor comprising a first terminal coupled to the gate electrode of the driving transistor and a second terminal coupled to the first electrode of the light emitting device;

a second transistor comprising;

a first electrode coupled to the gate electrode of the driving transistor;

a second electrode coupled to the first electrode of the driving transistor; and

a gate electrode;

a third transistor for applying a first power supply voltage to the first electrode of the driving transistor in response to an emission control signal;

a fourth transistor comprising a first electrode for receiving to a data signal and a second electrode coupled to the first terminal of the first capacitor;

a fifth transistor comprising;

a first electrode for receiving a reference voltage;

a second electrode coupled to the first terminal of the first capacitor; and

a gate electrode; and

a sixth transistor comprising;

a first electrode for receiving a first voltage;

a second electrode coupled to the gate electrode of the driving transistor; and

a gate electrode,

wherein the driving transistor and the second to sixth transistors are N-type transistors.

2. The pixel circuit of claim 1, wherein the sixth transistor is configured to apply the first voltage to the gate electrode of the driving transistor in response to a first scan signal applied to the gate electrode of the sixth transistor.

3. The pixel circuit of claim 2, wherein the fifth transistor is configured to apply the reference voltage to the first terminal of the first capacitor in response to a second scan signal applied to the gate electrode of the fifth transistor, and the second transistor is configured to diode-connect the driving transistor in response to the second scan signal applied to the gate electrode of the second transistor.

4. The pixel circuit of claim 3, wherein the second scan signal is a scan signal of an n^th period.

5. The pixel circuit of claim 4, wherein the first scan signal and the second scan signal are both maintained at the high signal level during an overlap period.

6. The pixel circuit of claim 5, wherein the second scan signal is maintained at a high signal level for a duration greater than the overlap period.

7. The pixel circuit of claim 2, wherein the first scan signal is a scan signal of an (n−

2)^th period.

8. The pixel circuit of claim 1, wherein the fourth transistor transfers the data signal to the first terminal of the first capacitor in response to a third scan signal applied to the gate electrode of the fourth transistor.

9. The pixel circuit of claim 8, wherein the third scan signal is a scan signal of an (n+3)^th period.

10. The pixel circuit of claim 1, wherein the light emitting device is an organic light emitting diode (OLED).

11. The pixel circuit of claim 1, wherein the driving transistor and the second to sixth transistors are N-type metal-oxide semiconductor field effect transistors (MOSFETs).

12. The pixel circuit of claim 1, wherein the first electrode of the driving transistor is a drain electrode and the second electrode of the driving transistor is a source electrode.

13. The pixel circuit of claim 1, wherein the first voltage applied to the first electrode of the sixth transistor is the first power supply voltage.

14. The pixel circuit of claim 1, wherein the first voltage applied to the first electrode of the sixth transistor is an initial voltage.

15. The pixel circuit of claim 1, wherein the first voltage applied to the first electrode of the sixth transistor is the reference voltage.

16. A method of driving a pixel circuit comprising an organic light emitting diode (OLED), a driving transistor, a plurality of switching transistors configured to turned on in response to first to third scan signals and an emission control signal, a plurality of storage capacitors, and a boosting capacitor coupled between first electrodes of boosting transistors, wherein the driving transistor, the switching transistors, and the boosting transistors are NMOS transistors, the method comprising:

initializing the pixel circuit when the first scan signal has a high signal level;

diode-connecting the driving transistor to compensate for a threshold voltage of the driving transistor when the second scan signal has the high signal level;

writing a data signal in the pixel circuit when the third scan signal has the high signal level; and

flowing a current through the OLED to emit light in response to the written data signal when the emission control signal has the high signal level.

17. The method of claim 16, wherein the first scan signal and the second scan signal are both maintained at the high signal level during an overlap period.

18. The method of claim 16, wherein the second scan signal is maintained at a high signal level for a duration greater than the overlap period.

19. An organic electro-luminescent display apparatus comprising:

a scan driver for supplying a scan signal to a plurality of scan lines;

an emission control driver for supplying an emission control signal to a plurality of emission control lines;

a data driver for supplying a data signal to a plurality of data lines; and

a plurality of pixel circuits located at crossing regions of the scan lines, the emission control lines and the data lines, wherein each pixel circuit of the plurality of pixel circuits comprises;

an organic light emitting diode (OLED) comprising a first electrode and a second electrode;

a driving transistor comprising;

a first electrode;

a second electrode; and

a gate electrode, the driving transistor for outputting a driving current according to a voltage applied to the gate electrode of the driving transistor;

a first capacitor comprising a first terminal and a second terminal coupled to the gate electrode of the driving transistor;

a second capacitor comprising a first terminal coupled to the gate electrode of the driving transistor and a second terminal coupled to the first electrode of the OLED;

a second transistor comprising;

a first electrode coupled to the gate electrode of the driving transistor;

a second electrode coupled to the first electrode of the driving transistor; and

a gate electrode;

a third transistor for applying a first power supply voltage to the first electrode of the driving transistor in response to the emission control signal;

a fourth transistor comprising;

a first electrode coupled to the data signal, a second electrode coupled to the first terminal of the first capacitor; and

a gate electrode;

a fifth transistor comprising;

a first electrode coupled to a reference voltage;

a second electrode coupled to the first terminal of the first capacitor; and

a gate electrode; and

a sixth transistor comprising;

a first electrode coupled to the first power supply voltage;

a second electrode coupled to the gate electrode of the driving transistor; and

a gate electrode,

wherein the driving transistor and the second to sixth transistors are N-type transistors.

20. The organic electro-luminescent display apparatus of claim 19, wherein the gate electrode of the sixth transistor is coupled to an (n−

2)^th scan line of the scan lines and is configured to apply the first power supply voltage to the gate electrode of the driving transistor in response to the scan signal applied to the gate electrode of the sixth transistor.

21. The organic electro-luminescent display apparatus of claim 19, wherein the gate electrode of the fifth transistor is coupled to an n^th scan line of the scan lines and is configured to apply the reference voltage to the first terminal of the first capacitor in response to the scan signal applied to the gate electrode of the fifth transistor.

22. The organic electro-luminescent display apparatus of claim 19, wherein the gate electrode of the second transistor is coupled to an n^th scan line of the scan lines and is configured to diode-connect the driving transistor in response to the scan signal applied to the gate electrode of the second transistor.

23. The organic electro-luminescent display apparatus of claim 19, wherein the gate electrode of the fourth transistor is coupled to an (n+3)^th scan line of the scan lines and is configured to transfer the data signal to the first terminal of the first capacitor in response to the scan signal applied to the gate electrode of the fourth transistor.