Method and system for programming and driving active matrix light emitting device pixel

• US 7,800,565 B2
• Filed: 12/07/2005
• Issued: 09/21/2010
• Est. Priority Date: 12/07/2004
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Chaji, Gholamreza Reza, Nathan, Arokia, Servatl, Peyman
• Primary Examiner(s): Nguyen; Chanh
• Assistant Examiner(s): PHAM, LONG D
• Application Number:
  US11/298,240
• Publication Number:
  US 20060176250A1
• Time in Patent Office: 1,749 Days
• Field of Search: 345 76- 86, 345204-215, 315/169.1, 315/169.3
• US Class Current: 345/82
• CPC Class Codes: G09G 2300/0465 Improved aperture ratio, e.g. by size reduction of the pixel circuit, e.g. for improving the pixel density or the maximum displayable luminance or brightness
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• 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 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element
• CPC Class Codes: G09G 3/3696 Generation of voltages supplied to electrode drivers

Abstract

Method and system for programming and driving active matrix light emitting device pixel is provided. The pixel is a voltage programmed pixel circuit, and has a light emitting device, a driving transistor and a storage capacitor. The pixel has a programming cycle having a plurality of operating cycles, and a driving cycle. During the programming cycle, the voltage of the connection between the OLED and the driving transistor is controlled so that the desired gate-source voltage of a driving transistor is stored in a storage capacitor.

Claims

1. A method of programming and driving a display system, the display system includes:

a display array having a plurality of pixel circuits arranged in row and column, each pixel circuit having;

a light emitting device having a first terminal and a second terminal;

a driving transistor having a gate terminal, a first terminal and a second terminal, the first terminal of the driving transistor being connected to the first terminal of the light emitting device, either the second terminal of the light emitting device or the second terminal of the driving transistor being connected to a controllable voltage supply line having a voltage and the other being connected to a voltage supply electrode;

a first capacitor and a second capacitor connected in series between the gate terminal of the driving transistor and a potential, each having a first terminal and a second terminal;

a first switch transistor having a gate terminal, a first terminal and a second terminal, the gate terminal of the first switch transistor being connected to a first select line, the first terminal of the first switch transistor being connected to the first terminal of the driving transistor, the second terminal of the first switch being connected to the first terminal of the first capacitor and the gate terminal of the driving transistor;

a second switch transistor having a gate terminal, a first terminal and a second terminal, the gate terminal of the second switch transistor being connected to a second select line, the first terminal of the second switch transistor being connected to a signal line having a voltage, the second terminal of the second switch transistor being connected to the second terminal of the first capacitor and the first terminal of the second capacitor;

the method comprising the steps of;

in a programming cycle having a plurality of operation cycles comprising a first operating cycle, a second operating cycle, a third operating cycle and a fourth operating cycle, setting the voltage on the controllable voltage supply line to at least a first voltage level and a second voltage level and setting the voltage on the signal line to at least a third voltage level, a fourth voltage level, and a fifth voltage level during the plurality of operation cycles to store a voltage associated with a threshold voltage of the driving transistor and a programming voltage in the first capacitor;

in the first operating cycle, setting the voltage on the controllable voltage supply line to the first voltage level and setting the voltage on the signal line to the fifth voltage level;

in the second operating cycle, setting the voltage on the signal line to the third voltage level and setting the voltage on the controllable voltage supply line to the first voltage level;

in the third operating cycle, setting the voltage on the controllable voltage supply line to the second voltage level and setting the voltage on the signal line to the fourth voltage level;

in the fourth operating cycle, setting the voltage on the signal line to the fifth voltage level and setting the voltage on the controllable voltage supply line to the second voltage level; and

in a driving cycle, applying the voltage stored in the first capacitor to the gate terminal of the driving transistor.

2. The method according to claim 1, wherein the light emitting device is an organic light emitting diode.

3. The method according to claim 1, wherein at least one of the transistors is a thin film transistor.

4. The method according to claim 1, wherein the first and second select lines are a common select line.

5. The method according to claim 1, wherein the programming cycle and the driving cycle for a row is overlapped with the programming cycle and the driving cycle for an adjacent row.

6. The method according to claim 1, wherein the step of changing comprises:

changing the voltage on the controllable voltage supply line in a stepwise manner.

7. The method according to claim 1, wherein

changing the voltage on the signal line in a stepwise manner.

8. The method according to claim 1, wherein

changing the voltage on the controllable voltage supply line and the voltage on the signal line in a stepwise manner.

9. The method according to claim 8, comprising:

in the programming cycle, operating on the first select line to turn the first switch transistor on and off.

10. The method according to claim 8, comprising:

in the programming cycle, operating on the second select line to select the second switch transistor.

11. The method according to claim 1, wherein the second voltage level is associated with a reference voltage, and wherein the fourth voltage level is associated with the reference voltage and the programming voltage.

12. The method according to claim 1, wherein

in the fourth operating cycle, setting the voltage on the signal line to a voltage level of the fifth voltage in the first operating cycle.

13. The method according to claim 1, wherein in the forth fourth operating cycle, setting the second terminal of the first capacitor and the first terminal of the second capacitor to the fifth voltage level.

14. The method according to claim 1, wherein in the second operating cycle, setting the first terminal of the driving transistor to the first voltage level.

15. The method according to claim 1, wherein the voltage associated with the threshold voltage of the driving transistor and the programming voltage is (VT+VP) or −

(VT+VP) where VT represents the threshold voltage of the driving transistor, VP represents the programming voltage.

16. A display system comprising:

a display array having a plurality of pixel circuits arranged in row and column, each pixel circuit having;

a light emitting device having a first terminal and a second terminal;

a driving transistor having a gate terminal, a first terminal and a second terminal, the first terminal of the driving transistor being connected to the first terminal of the light emitting device, either the second terminal of the light emitting device or the second terminal of the driving transistor being connected to a controllable voltage supply line and the other being connected to a voltage supply electrode;

a first capacitor and a second capacitor connected in series between the gate terminal of the driving transistor and a potential, each having a first terminal and a second terminal;

a first switch transistor having a gate terminal, a first terminal and a second terminal, the gate terminal of the first switch transistor being connected to a first select line, the first terminal of the first switch transistor being connected to the first terminal of the driving transistor, the second terminal of the first switch being connected to the first terminal of the first capacitor and the gate terminal of the driving transistor;

a second switch transistor having a gate terminal, a first terminal and a second terminal, the gate terminal of the second switch transistor being connected to a second select line, the first terminal of the second switch transistor being connected to a signal line, the second terminal of the second switch transistor being connected to the second terminal of the first capacitor and the first terminal of the second capacitor;

the pixel circuit being programmed in a programming cycle and emitting light in a driving cycle,

the controllable voltage supply line having a voltage, the voltage on the controllable voltage supply line being changed to at least a first voltage level and a second voltage level and the signal line having a voltage, the voltage on the signal line being changed to at least a third voltage level, a fourth voltage level and a fifth voltage level during the plurality of operation cycles in the programming cycle to store a voltage associated with a threshold voltage of the driving transistor and a programming voltage in the first capacitor;

wherein the programming cycle comprises a first operating cycle, a second operating cycle, a third operating cycle, and a fourth operating cycle, and the programming cycle comprising;

in the first operating cycle, setting a voltage on the controllable voltage supply line to the first voltage level and setting the voltage on the signal line to the fifth voltage level;

in the second operating cycle, setting the voltage on the signal line to the third voltage level and setting the voltage on the controllable voltage supply line to the first voltage level;

in the third operating cycle, setting the voltage on the controllable voltage supply line to the second voltage level and setting the voltage on the signal line to the fourth voltage level;

in the fourth operating cycle, setting the voltage on the signal line to the fifth voltage level and setting the voltage on the controllable voltage supply line to the second voltage level; and

the driving cycle comprising applying the voltage stored in the first capacitor to the gate terminal of the driving transistor.

17. The display system according to claim 16, wherein the light emitting device is an organic light emitting diode.

18. The display system according to claim 16, wherein at least one of the transistors is a thin film transistor.

19. The display system according to claim 16, wherein the first and second select lines are a common select line.

20. The display system according to claim 16, wherein the programming cycle and the driving cycle for a row is overlapped with the programming cycle and the driving cycle for an adjacent row.

21. The display system according to claim 16, comprising:

a driver for driving the first select line, the second select line, the controllable voltage supply line and the signal line to operate the display array; and

a controller for controlling the driver to implement the programming cycle and the driving cycle.

22. The display system according to claim 21, wherein the driver changes the voltage on the controllable voltage supply line in a stepwise manner, in the programming cycle.

23. The display system according to claim 21, wherein the driver changes the voltage on the signal line in a stepwise manner, in the programming cycle.

24. The display system according to claim 21, wherein the driver changes the voltage on the controllable voltage supply line and the voltage on the signal line in a stepwise manner, in the programming cycle.

25. The display system according to claim 24, wherein the driver operates on the first select line to turn the first switch transistor on and off, in the programming cycle.

26. The display system according to claim 24, wherein the driver operates on the second select line to select the second switch transistor, in the programming cycle.

27. The display system according to claim 16, wherein the voltage associated with the threshold voltage of the driving transistor and the programming voltage is (VT+VP) or −

(VT+VP) where VT represents the threshold voltage of the driving transistor, VP represents the programming voltage.