DISPLAY DEVICE AND DRIVING METHOD THEREOF

• US 20100164847A1
• Filed: 08/21/2009
• Published: 07/01/2010
• Est. Priority Date: 12/29/2008
• Status: Active Grant

• Current Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Inventors: PARK, Seong-II, Lee, Baek-Woon, PARK, Kyong-Tae
• Granted Patent: US 8,289,313 B2
• Time in Patent Office: Days
• US Class Current: 345/77
• 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 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2310/0256 with the purpose of reversing the voltage across a light emitting or modulating element within a pixel
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

In a display device, the anode voltage of an organic light emitting element is periodically reset. The control terminal of a driving transistor is periodically reset, and an input data voltage is connected to the control terminal through an input terminal and an output terminal of the driving transistor. As a result, good control over the displayed luminance is achieved. Other features are also provided.

Claims

1. A display device comprising one or more pixels, each pixel being associated with a first signal, a second signal, a third signal, and a fourth signal, each pixel comprising:

(a) a light-emitting device;

(b) a driving transistor for outputting a current to the light-emitting device, the driving transistor comprising an input terminal, an output terminal, and a control terminal;

(c) a data voltage terminal for receiving data voltages;

(d) a plurality of switching transistors comprising;

(1) a switching transistor controlled by the associated first signal, and connected between the data voltage and the input terminal of the driving transistor;

(2) a switching transistor controlled by the associated second signal, and connected between a driving voltage terminal and the input terminal of the driving transistor;

(3) a switching transistor controlled by the associated third signal, and connected between an output terminal of the driving transistor and a first terminal of the light-emitting device;

(4) a switching transistor controlled by the associated fourth signal, and connected between the output terminal of the driving transistor and the control terminal of the driving transistor;

wherein each pixel further comprises a first capacitor connected between the control terminal of the driving transistor and the driving voltage terminal;

wherein the display device further comprises a control circuit for generating control signals which include the first, second, third and fourth signals associated with the one or more pixels, the control signals being generated for one or more consecutive first periods of time and acting to reset a voltage at the first terminal of the light-emitting device in each first period of time.

2. The display device of claim 1, wherein:

the one or more pixels comprise a plurality of rows of pixels;

the pixels in each row share an associated plurality of the control signals, the associated plurality being associated with the row and comprising a single first signal, a single second signal, a single third signal, and a single fourth signal.

3. The display device of claim 2, wherein:

the first terminal of the light-emitting device is an anode, and each first period is a frame.

4. The display device of claim 2, wherein the control circuit is for generating the control signals for each pixel so that:

each pixel is associated with consecutive first, second, third and fourth intervals of time; and

during at least part of the first interval, the switching transistors in (1) and (2) are turned off and the switching transistors in (3) and (4) are turned on,

during at least part of the second interval, the switching transistors in (1) and (4) are turned on and the switching transistors in (2) and (3) are turned off,

during at least part of the third interval, the switching transistor (1) is turned on and the switching transistors (2), (3), and (4) are turned off, and

during at least part of the fourth interval, the switching transistors (1) and (4) are turned off and the switching transistors (2) and (3) are turned on.

5. The display device of claim 4, wherein the control circuit is for generating the control signals so that, in each pixel:

the light-emitting device stops emitting light during the first, second, and third intervals, and the light-emitting device emits light during the fourth interval.

6. The display device of claim 4, wherein the control circuit is for generating the control signals so that, in each pixel:

an interval in which the light-emitting device emits light is controlled by the second signal.

7. The display device of claim 4, wherein the control circuit is for generating the control signals so that, in each pixel:

the voltage at the first terminal of the light-emitting device is reset during the first interval.

8. The display device of claim 2, wherein, in each pixel, the switching transistors (1), (2), (3), (4), and the driving transistor are p-channel electric field effect transistors.

9. The display device of claim 2, wherein each pixel is associated with a fifth signal which is one of the control signals, and wherein in each pixel, the plurality of switching transistors further comprises:

(5) a switching transistor connected between a reset voltage terminal and the switching transistor (3) and controlled by the associated fifth signal.

10. The display device of claim 9, wherein the control circuit is for generating the control signals for each pixel so that:

each pixel is associated with consecutive first, second, third and fourth intervals of time and with a fifth interval of time which precedes the first interval of time; and

during at least part of the first interval, the switching transistors (1) and (2) are turned off and the switching transistors (3) and (4) are turned on,

during at least part of the second interval, the switching transistors (1) and (4) are turned on and the switching transistors (2) and (3) are turned off,

during at least part of the third interval, the switching transistor (1) is turned on and the switching transistors (2), (3), and (4) are turned off,

during at least part of the fourth interval, the switching transistors (1) and (4) are turned off and the switching transistors (2) and (3) are turned on, and

during at least part of the fifth interval, the switching transistors (1), (2), and (4) are turned off and the switching transistor (3) is turned on.

11. The display device of claim 10, wherein the control circuit is for generating the control signals for each pixel so that:

the switching transistor (5) is turned on during at least part of the first interval and at least part of the fifth interval, and is turned off during at least part of the second interval, at least part of the third interval, and at least part of the fourth interval.

12. The display device of claim 9, wherein in each pixel, the switching transistor (5) is connected between the switching transistor (3) and the first terminal of the light-emitting device.

13. The display device of claim 9, wherein in each pixel, the switching transistor (5) is connected between the switching transistor (3) and the first terminal of the light-emitting device.

14. The display device of claim 10, wherein the control circuit is for generating the control signals so that, in each pixel:

the light-emitting device stops emitting light during the first, second, and third intervals, and the light-emitting device emits light during the fourth interval.

15. The display device of claim 14, wherein the control circuit is for generating the control signals so that, in each pixel:

an interval in which the light-emitting device emits light is controlled by the second signal.

16. The display device of claim 10, wherein the control circuit is for generating the control signals so that, in each pixel:

the voltage at the first terminal of the light-emitting device is reset during the first interval and the fifth interval.

17. The display device of claim 9, wherein in each pixel, the switching transistors (1), (2), (3), (4), and (5) and the driving transistor are p-channel electric field effect transistors.

18. The display device of claim 9, wherein in each pixel, the switching transistors (1), (2), (3), and (4) and the driving transistor are p-channel electric field effect transistors, and the switching transistor (5) is an n-channel electric field effect transistor.

19. The display device of claim 9, wherein in each pixel, the switching transistors (2) and (3) and the driving transistor are p-channel electric field effect transistors, and the switching transistors (1), (4), and (5) are n-channel electric field effect transistors.

20. The display device of claim 9, wherein each pixel is associated with a sixth signal which is one of the control signals, and wherein in each pixel, the plurality of switching transistors further comprises:

(6) a switching transistor connected to the control terminal of the driving transistor and to a terminal for receiving a sustain voltage, the switching transistor (6) being controlled by the associated sixth signal;

wherein each pixel further comprises a second capacitor connected between the control terminal of the driving transistor and a control terminal of the first switching transistor, and

wherein for each pixel, the associated second signal coincides with the associated third signal, and the associated fifth signal coincides with the associated sixth signal.

21. The display device of claim 20, wherein the control circuit is for generating the control signals for each pixel so that:

each pixel is associated with consecutive first, second, third and fourth intervals of time; and

during at least part of the first interval, the switching transistors (1), (2), (3), and (4) are turned off and the switching transistors (5) and (6) are turned on,

during at least part of the second interval, the switching transistors (1) and (4) are turned on and the switching transistors (2), (3), (5), and (6) are turned off,

during at least part of the third interval, the switching transistors (1) to (6) are turned off, and

during at least part of the fourth interval, the switching transistors (1), (4), (5), and (6) are turned off and the switching transistors (2) and (3) are turned on.

22. The display device of claim 21, wherein the control circuit is for generating the control signals so that, in each pixel:

the voltage at the first terminal of the light-emitting device is reset during the first interval.

23. The display device of claim 9, wherein each pixel is associated with a sixth signal which is one of the control signals, and wherein in each pixel, the plurality of switching transistors further comprises:

(6) a switching transistor connected to the control terminal of the driving transistor and to a terminal for receiving a sustain voltage, the switching transistor (6) being controlled by the associated sixth signal;

wherein each pixel further comprises a second capacitor connected between the control terminal of the driving transistor and a control terminal of the first switching transistor, and

wherein for each pixel, the associated second, third, and fifth signals are the same signal.

24. The display device of claim 23, wherein the control circuit is for generating the control signals for each pixel so that:

each pixel is associated with consecutive first, second, third and fourth intervals of time; and

during at least part of the first interval, the switching transistors (1), (2), (3), and (4) are turned off and the switching transistors (5) and (6) are turned on,

during at least part of the second interval, the switching transistors (1), (4), and (5) are turned on and the switching transistors (2), (3), and (6) are turned off,

during at least part of the third interval, the switching transistors (1), (2), (3), (4), and (6) are turned off and the switching transistor (5) is turned on, and

during at least part of the fourth interval, the switching transistors (1), (4), (5), and (6) are turned off and the switching transistors (2) and (3) are turned on.

25. A method for driving a display device including an organic light emitting element and a driving transistor, the method comprising:

resetting a voltage at a control terminal of the driving transistor;

resetting a voltage at a first terminal of the organic light emitting element, the first terminal being at a variable voltage during operation;

connecting a data voltage to the control terminal of the driving transistor to charge the control terminal to a first voltage depending on the data voltage; and

emitting, by the organic light emitting element, light corresponding to the first voltage at the control terminal.

26. The method of claim 25, further comprising

displaying black by the organic light emitting element irrespective of the data voltage.

27. The method of claim 25, wherein connecting the data voltage to the control terminal of the driving transistor comprises connecting the data voltage to an input terminal of the driving transistor and to an output terminal of the driving transistor.

28. The method of claim 25, wherein

the display device further includes a switching transistor for providing a data voltage to an input terminal of the driving transistor in response to a scanning signal, a driving voltage transistor connected between a driving voltage terminal and the input terminal of the driving transistor, a light-emitting device transistor connected between the first terminal of the organic light emitting element and an output terminal of the driving transistor, and a compensation transistor connected between the output and control terminals of the driving transistor, and

the resetting of the voltage at the control terminal and the resetting of the voltage at the first terminal of the organic light emitting element are performed simultaneously.

29. The method of claim 28, wherein

the resetting of the voltage at the control terminal and the resetting of the voltage at the first terminal of the organic light emitting element are performed by turning on the compensation transistor and the light-emitting device transistor.

30. The method of claim 28, wherein

the connecting of the data voltage to the control terminal of the driving transistor is performed by turning on the switching transistor and the compensation transistor when the control terminal is reset.

31. The method of claim 28, wherein

the emitting of light by the organic light emitting element is performed by turning on the driving voltage transistor and the light-emitting device transistor.

32. The method of claim 28, wherein

the switching transistor and the compensation transistor are turned on for about two horizontal periods in each frame.

33. The method of claim 32, wherein

the light-emitting device transistor is turned off for about two horizontal periods in each frame.

34. The method of claim 25, wherein

the display device further includes a switching transistor for providing the data voltage to an input terminal of the driving transistor in response to a scanning signal, a driving voltage transistor connected between a driving voltage terminal and the input terminal of the driving transistor, a light-emitting device transistor connected between the first terminal of the organic light emitting element and an output terminal of the driving transistor, a compensation transistor connected between the output and control terminals of the driving transistor, and a reset transistor for resetting the voltage at the first terminal of the organic light emitting element, and

the resetting of the voltage at the first terminal of the organic light emitting element is performed by turning on the reset transistor.

35. The method of claim 34, wherein

the resetting of the control terminal is performed by turning on the compensation transistor, the reset transistor, and the light-emitting device transistor.

36. The method of claim 34, wherein

the connecting of the data voltage to the control terminal of the driving transistor is performed by turning on the switching transistor and the compensation transistor when the control terminal is reset.

37. The method of claim 34, wherein

the emitting of light by the organic light emitting element is performed by turning on the driving voltage transistor and the light-emitting device transistor.

38. The method of claim 34, wherein

the switching transistor, the compensation transistor, and the reset transistor are turned on for about two horizontal periods in each frame.

39. The method of claim 38, wherein

the light-emitting device transistor is turned off for about two horizontal periods in each frame.

40. The method of claim 25, wherein

the display device further includes a switching transistor for providing the data voltage to an input terminal of the driving transistor in response to a scanning signal, a driving voltage transistor connected between the driving voltage terminal and the input terminal of the driving transistor, a light-emitting device transistor connected between the first terminal of the organic light emitting element and an output terminal of the driving transistor, a compensation transistor connected between the output and control terminals of the driving transistor, a first reset transistor for resetting the voltage at the first terminal of the organic light emitting element, and a second reset transistor connected to the control terminal of the driving transistor, and

the resetting of the voltage at the first terminal of the organic light emitting element is performed by turning on the first reset transistor.

41. The method of claim 40, wherein

the resetting of the control terminal is performed by turning on the second reset transistor.

42. The method of claim 41, wherein

the resetting of the voltage at the first terminal of the organic light emitting element and the resetting of the control terminal are performed simultaneously.

43. The method of claim 40, wherein

the connecting of the data voltage to the control terminal of the driving transistor is performed by turning on the switching transistor and the compensation transistor when the control terminal is reset.

44. The method of claim 40, wherein

the emitting of light by the organic light emitting element is performed by turning on the driving voltage transistor and the light-emitting device transistor.