SYSTEM AND DRIVING METHOD FOR LIGHT EMITTING DEVICE DISPLAY

• US 20100039458A1
• Filed: 04/17/2009
• Published: 02/18/2010
• Est. Priority Date: 04/18/2008
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: ALEXANDER, Stefan, CHAJI, G. Reza, NATHAN, Arokia
• Granted Patent: US 8,614,652 B2
• Time in Patent Office: Days
• US Class Current: 345/698
• CPC Class Codes: G09G 2300/043 Compensation electrodes or other additional electrodes in matrix displays related to distortions or compensation signals, e.g. for modifying TFT threshold voltage in column driver
• 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 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 2310/0262 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 2320/0252 Improving the response speed
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3241 the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element
• CPC Class Codes: G09G 3/3283 in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices
• 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]

Abstract

A light emitting device display, its pixel circuit and its driving technique is provided. The pixel includes a light emitting device and a plurality of transistors. A bias current and programming voltage data are provided to the pixel circuit in accordance with a driving scheme so that the current through the driving transistor to the light emitting device is adjusted.

Claims

1. A pixel circuit comprising:

a light emitting device;

a driving transistor for providing a pixel current to the light emitting device, the driving transistor having a gate terminal, a first terminal coupled to the light emitting device, and a second terminal;

a storage capacitor provided between a data line for providing programming voltage data and the gate terminal of the driving transistor;

a first switch transistor provided between the gate terminal of the driving transistor and the first terminal of the driving transistor; and

a second switch transistor provided between the first terminal of the driving transistor and a bias line for providing a bias current to the first terminal of the driving transistor during a programming cycle.

2. A pixel circuit as claimed in claim 1, wherein the gate terminal of the first switch transistor and the gate terminal of the second switch transistor are operated by a single select line.

3. A pixel circuit as claimed in claim 1, wherein the second switch transistor includes a first terminal coupled to the bias line and a second terminal coupled to a connection node between the light emitting device and the driving transistor.

4. A pixel circuit as claimed in claim 1, wherein the programming voltage data includes a plurality of voltage signals for dividing current in different current levels for different gray scales.

5. A pixel circuit as claimed in claim 1, wherein the light emitting device includes an organic light emitting diode.

6. A pixel circuit as claimed in claim 1, wherein at least one of the transistors is a thin film transistor.

7. A pixel circuit as claimed in claim 1, wherein the transistor is implemented using poly silicon, nano/micro (crystalline) silicon, amorphous silicon, CMOS, organic semiconductor, metal organic technologies, or combination thereof.

8. A pixel circuit as claimed in claim 1, wherein the pixel circuit forms an active matrix array.

17. A display system, comprising:

a pixel array having a plurality of pixel circuits, each defined in claim 1;

a first driver for selecting the pixel circuit;

a second driver for providing the programming voltage data; and

a current source for operating on the bias line.

18. A display system as claimed in claim 17, wherein the current source comprises at least one of:

a calibrated current mirror for operating on the bias line based on a reference current;

a voltage to current convertor for converting voltage to the bias current.

19. A display system as claimed in claim 17, wherein the current source is calibrated via a data stored in a memory.

25. A pixel circuit as claimed in claim 1, wherein the bias current is a predetermined fixed current.

9. A pixel circuit comprising:

a light emitting device;

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

a driving transistor for providing a pixel current to the light emitting device, the driving transistor having a gate terminal, a first terminal coupled to the first terminal of the storage capacitor, and a second terminal coupled to the light emitting device;

a first switch transistor operated by a first select line and provided between the second terminal of the storage capacitor and a data line for providing programming voltage data;

a second switch transistor operated by the first select line and provided between the first terminal of the storage capacitor and a bias line for providing a bias current to the first terminal of the driving transistor during a programming cycle; and

an emission control circuit for setting the pixel circuit into an emission mode.

10. A pixel circuit as claimed in claim 9, wherein the emission control circuit comprises:

a third switch transistor coupled between a first potential and the first terminal of the driving transistor;

a fourth switch transistor coupled between the second terminal of the storage capacitor and the gate terminal of the driving transistor; and

a fifth switch transistor coupled between the gate terminal of the driving transistor and a second potential.

11. A pixel circuit as claimed in claim 10, wherein the third and fourth switch transistors are operated by a second select line, and wherein the fifth switch transistor is operated by the first select line.

12. A pixel circuit as claimed in claim 9, wherein the programming voltage data includes a plurality of voltage signals for dividing current in different current levels for different gray scales.

13. A pixel circuit as claimed in claim 9, wherein the light emitting device includes an organic light emitting diode.

14. A pixel circuit as claimed in claim 9, wherein at least one of the transistors is a thin film transistor.

15. A pixel circuit as claimed in claim 9, wherein the transistor is implemented using poly silicon, nano/micro (crystalline) silicon, amorphous silicon, CMOS, organic semiconductor, metal organic technologies, or combination thereof.

16. A pixel circuit as claimed in claim 9, wherein the pixel circuit forms an active matrix array.

20. A display system, comprising:

a pixel array having a plurality of pixel circuits, each defined in claim 9;

a first driver for selecting the pixel circuit;

a second driver for providing the programming voltage data; and

a current source for operating on the bias line.

21. A display system as claimed in claim 20, wherein the current source comprises at least one of:

a calibrated current mirror for operating on the bias line based on a reference current;

a voltage to current convertor for converting voltage to the bias current.

22. A display system as claimed in claim 20, wherein the current source is calibrated via a data stored in a memory.

26. A pixel circuit as claimed in claim 9, wherein the bias current is a predetermined fixed current.

23. A method of driving a pixel circuit, the pixel circuit having a driving transistor for providing a pixel current to a light emitting device, a storage capacitor coupled to a data line, and a switch transistor coupled to the gate terminal of the driving transistor and the storage capacitor, the method comprising:

at a programming cycle, selecting the pixel circuit, providing a bias current to a connection between the driving transistor and the light emitting device, and providing programming voltage data from the data line to the pixel circuit.

27. A method as claimed in claim 23, wherein the bias current is a predetermined fixed current.

24. A method of driving a pixel circuit, the pixel circuit having a driving transistor for providing a pixel current to a light emitting device, a switch transistor coupled to a data line, and a storage capacitor coupled to the switch transistor and the driving transistor, the method comprising:

at a programming cycle, selecting the pixel circuit, providing a bias current to a first terminal of the driving transistor, and providing programming voltage data from the data line to a first terminal of the storage capacitor, the second terminal of the storage capacitor being coupled to the first terminal of the driving transistor, a second terminal of the driving transistor being coupled to the light emitting device; and

at a driving cycle, setting an emission mode in the pixel circuit.

28. A method as claimed in claim 24, wherein the bias current is a predetermined fixed current.