Light emitting device, method of driving a light emitting device, element substrate, and electronic equipment

• US 20030062524A1
• Filed: 08/29/2002
• Published: 04/03/2003
• Est. Priority Date: 08/29/2001
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Kimura, Hajime
• Granted Patent: US 7,046,240 B2
• Time in Patent Office: Days
• US Class Current: 257/72
• CPC Class Codes: G09G 2300/0814 used for selection purposes, e.g. logical AND for partial update
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with 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 2310/061 for resetting or blanking
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/3208 organic, e.g. using organic light-emitting diodes [OLED]
• CPC Class Codes: G09G 3/3225 using an active matrix
• 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 3/3283 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: H01L 2029/7863 with an LDD consisting of more than one lightly doped zone or having a non-homogeneous dopant distribution, e.g. graded LDD
• CPC Class Codes: H01L 27/12 the substrate being other than a semiconductor body, e.g. an insulating body
• CPC Class Codes: H01L 27/1214 comprising a plurality of TFTs formed on a non-semiconducting substrate, e.g. driving circuits for AMLCDs
• CPC Class Codes: H01L 29/42384 for thin film field effect transistors, e.g. characterised by the thickness or the shape of the insulator or the dimensions, the shape or the lay-out of the conductor
• CPC Class Codes: H01L 29/4908 for thin film semiconductor, e.g. gate of TFT
• CPC Class Codes: H01L 29/66757 Lateral single gate single channel transistors with non-inverted structure, i.e. the channel layer is formed before the gate
• CPC Class Codes: H01L 29/78621 with LDD structure or an extension or an offset region or characterised by the doping profile
• CPC Class Codes: H10K 50/84 Passivation; Containers; Encapsulations
• CPC Class Codes: H10K 50/841 Self-supporting sealing arrangements
• CPC Class Codes: H10K 50/844 Encapsulations
• CPC Class Codes: H10K 50/846 : comprising getter material or desiccants
• CPC Class Codes: H10K 59/12 : Active-matrix OLED [AMOLED] displays

Abstract

A display device capable of obtaining a constant luminance without being influenced by temperature change is provided as well as a method of driving the display device. A current mirror circuit composed of a first transistor and a second transistor is provided in each pixel. The first transistor and second transistor of the current mirror circuit are connected such that their drain currents are kept almost equal irrespective of the level of load resistance. By controlling the OLED drive current using the current mirror circuit, a change in OLED drive current due to fluctuation in characteristics between transistors is avoided and a constant luminance is obtained without being influenced by temperature change.

Claims

1. A light emitting device having a plurality of pixels each including a light emitting element,

wherein each of the pixels has means for converting a supplied current into a voltage and for supplying a first current to the light emitting element in an amount according to the voltage converted, and has means for supplying a second current to the light emitting element in an amount according to the voltage converted.

31. Electronic equipment comprising a light emitting device of claim 1.

2. A light emitting device having a plurality of pixels each including a light emitting element and means for supplying a current to the pixels in an amount determined by a video signal,

wherein each of the pixels has means for converting the supplied current into a voltage and for supplying a first current to the light emitting element in an amount according to the voltage converted, and has means for supplying a second current to the light emitting element in an amount according to the voltage converted.

32. Electronic equipment comprising a light emitting device of claim 2.

3. A light emitting device having a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a light emitting element, a power supply line, and a signal line,

wherein a source of the first transistor and a source of the second transistor are both connected to the power supply line,

wherein the first transistor and the second transistor are connected to each other at their gates,

wherein the third transistor has a source and a drain one of which is connected to the signal line and the other of which is connected to a drain of the first transistor,

wherein the fourth transistor has a source and a drain one of which is connected to the drain of the first transistor or to the signal line and the other of which is connected to the gates of the first and second transistors,

wherein the fifth transistor has a source and a drain one of which is connected to a drain of the first transistor and the other of which is connected to a drain of the second transistor, and

wherein the drain of the second transistor is connected to a pixel electrode of the light emitting element.

4. A light emitting device as claimed in claim 3, wherein the third transistor is connected to the gate of the fifth transistor.

5. A light emitting device as claimed in claim 3, wherein the third transistor and the fifth transistor have different polarities.

6. A light emitting device as claimed in claim 3, wherein the third transistor, the fourth transistor, and the fifth transistor are connected to each other at their gates.

7. A light emitting device as claimed in claim 3, wherein the third transistor and the fourth transistor have the same polarity, while the third transistor and the fourth transistor have different polarities from the fifth transistor.

19. A light emitting device according to claim 3, wherein the first transistor and the second transistor have the same polarity.

20. A light emitting device according to claim 4, wherein the first transistor and the second transistor have the same polarity.

21. A light emitting device according to claim 6, wherein the first transistor and the second transistor have the same polarity.

33. Electronic equipment comprising a light emitting device of claim 3.

34. Electronic equipment comprising a light emitting device of claim 4.

35. Electronic equipment comprising a light emitting device of claim 6.

8. A light emitting device having a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a light emitting element, a power supply line, and a signal line,

wherein the first transistor and the second transistor are connected to each other at their gates,

wherein the third transistor has a source and a drain one of which is connected to the signal line and the other of which is connected to sources of the first and second transistors,

wherein the fourth transistor has a source and a drain one of which is connected to the gates of the first and second transistors and the other of which is connected to the power supply line,

wherein the sixth transistor has a source and a drain one of which is connected to the power supply line and the other of which is connected to a drain of the second transistor, and

wherein the fifth transistor has a source and a drain one of which is connected to sources of the first and second transistors and the other of which is connected to a pixel electrode of the light emitting element.

10. A light emitting device according to claim 8, wherein the fifth transistor and the sixth transistor have the same polarity.

22. A light emitting device according to claim 8, wherein the first transistor and the second transistor have the same polarity.

36. Electronic equipment comprising a light emitting device of claim 8.

9. A light emitting device having a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a light emitting element, a power supply line, and a signal line,

wherein the first transistor and the second transistor are connected to each other at their gates,

wherein the third transistor has a source and a drain one of which is connected to the signal line and the other of which is connected to a source of the first transistor,

wherein the fourth transistor has a source and a drain one of which is connected to the gates of the first and second transistors and the other of which is connected to the power supply line,

wherein the fifth transistor has a source and a drain one of which is connected to the source of the first transistor and the other of which is connected to a pixel electrode of the light emitting element,

wherein the sixth transistor has a source and a drain one of which is connected to a source of the second transistor and the other of which is connected to the pixel electrode of the light emitting element, and

wherein a gate of the fifth transistor and a gate of the sixth transistor are connected to each other.

11. A light emitting device according to claim 9, wherein the fifth transistor and the sixth transistor have the same polarity.

23. A light emitting device according to claim 9, wherein the first transistor and the second transistor have the same polarity.

37. Electronic equipment comprising a light emitting device of claim 9.

12. A light emitting device having a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a light emitting element, a power supply line, and a signal line,

wherein a source of the first transistor and a source of the second transistor are both connected to the power supply line,

wherein the first transistor and the second transistor are connected to each other at their gates,

wherein the third transistor has a source and a drain one of which is connected to the signal line and the other of which is connected to a drain of the first transistor,

wherein the fourth transistor has a source and a drain one of which is connected to the drain of the first transistor or to the signal line and the other of which is connected to the gates of the first and second transistors,

wherein the fifth transistor has a source and a drain one of which is connected to a drain of the sixth transistor and the other of which is connected to a drain of the second transistor,

wherein a gate of the sixth transistor is connected to the gates of the first and second transistors,

wherein a source of the sixth transistor is connected to the drain of the first transistor, and

wherein the drain of the second transistor is connected to a pixel electrode of the light emitting element.

24. A light emitting device according to claim 12, wherein the first transistor and the second transistor have the same polarity.

38. Electronic equipment comprising a light emitting device of claim 12.

13. A light emitting device having a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a light emitting element, a power supply line, and a signal line,

wherein a source of the first transistor and a source of the second transistor are both connected to the power supply line,

wherein the first transistor and the second transistor are connected to each other at their gates,

wherein the third transistor has a source and a drain one of which is connected to the signal line and the other of which is connected to a drain of the first transistor,

wherein the fourth transistor has a source and a drain one of which is connected to the drain of the first transistor or to the signal line and the other of which is connected to the gates of the first and second transistors,

wherein the fifth transistor has a source and a drain one of which is connected to a drain of the first transistor and the other of which is connected to a source of the sixth transistor,

wherein a gate of the sixth transistor is connected to the gates of the first and second transistors,

wherein a drain of the sixth transistor is connected to the drain of the second transistor, and

wherein the drain of the second transistor is connected to a pixel electrode of the light emitting element.

25. A light emitting device according to claim 13, wherein the first transistor and the second transistor have the same polarity.

39. Electronic equipment comprising a light emitting device of claim 13.

14. A light emitting device having a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a light emitting element, a power supply line, and a signal line,

wherein the first transistor and the second transistor are connected to each other at their gates,

wherein the third transistor has a source and a drain one of which is connected to the signal line and the other of which is connected to a drain of the first transistor,

wherein the fourth transistor has a source and a drain one of which is connected to the drain of the first transistor or to the signal line and the other of which is connected to the gates of the first and second transistors,

wherein the fifth transistor has a source and a drain one of which is connected to a drain of the second transistor and the other of which is connected to a drain of the first transistor, and

wherein the sources of the first and second transistors are connected to a pixel electrode of the light emitting element.

26. A light emitting device according to claim 14, wherein the first transistor and the second transistor have the same polarity.

40. Electronic equipment comprising a light emitting device of claim 14.

15. A light emitting device having a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a light emitting element, a power supply line, and a signal line,

wherein the first transistor and the second transistor are connected to each other at their gates,

wherein the third transistor has a source and a drain one of which is connected to the signal line and the other of which is connected to a drain of the first transistor,

wherein the fourth transistor has a source and a drain one of which is connected to the drain of the first transistor or to the signal line and the other of which is connected to the gates of the first and second transistors,

wherein the fifth transistor has a source and a drain one of which is connected to a drain of the second transistor and the other of which is connected to a drain of the sixth transistor,

wherein the source of the sixth transistor is connected to the drain of the first transistor, and

wherein the sources of the first and second transistors are connected to a pixel electrode of the light emitting element.

27. A light emitting device according to claim 15, wherein the first transistor and the second transistor have the same polarity.

41. Electronic equipment comprising a light emitting device of claim 15.

16. A light emitting device having a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a light emitting element, a power supply line, and a signal line,

wherein the first transistor and the second transistor are connected to each other at their gates,

wherein the third transistor has a source and a drain one of which is connected to the signal line and the other of which is connected to a source of the first transistor,

wherein the fourth transistor has a source and a drain one of which is connected to the drain of the first transistor and the other of which is connected to the gates of the first and second transistors,

wherein the fifth transistor has a source and a drain one of which is connected to the source of the first transistor and the other of which is connected to a source of the second transistor,

wherein the drains of the first and second transistors are connected to the power supply line, and

wherein the source of the second transistor is connected to a pixel electrode of the light emitting element.

17. A light emitting device according to claim 16 further comprising a sixth transistor, wherein the sixth transistor has a source and a drain one of which is connected to the source of the second transistor and the other of which is connected to the source of the first transistor.

18. A light emitting device according to claim 16 further comprising a sixth transistor, wherein the sixth transistor has a source and a drain one of which is connected to the source of the second transistor and the other of which is connected to the source of the first transistor, and

wherein a gate of the fifth transistor and a gate of the sixth transistor are connected to each other.

28. A light emitting device according to claim 16, wherein the first transistor and the second transistor have the same polarity.

42. Electronic equipment comprising a light emitting device of claim 16.

29. A light emitting device having a plurality of pixels each including a light emitting element,

wherein each of the pixels has first and second means for converting the supplied current into a voltage, and

wherein the second means supplies a current to the light emitting element in an amount according to the voltage converted.

30. A light emitting device having a plurality of pixels and current supplying means, the pixels each including a light emitting element, the means supplying a current to the pixels in an amount determined by a video signal,

wherein each of the pixels has first and second means for converting the supplied current into a voltage, and

wherein the second means supplies a current to the light emitting element in an amount according to the voltage converted.

43. A method of driving a light emitting device that has a plurality of pixels each including a light emitting element,

wherein, in a first period, a current determined by a video signal is supplied to the pixels, and first means of each of the pixels converts the supplied current into a voltage, and

wherein, in a second period, the first means of each of the pixels supplies a first current to the light emitting element in an amount according to the voltage converted, and second means of each of the pixels supplies a second current to the light emitting element in an amount according to the voltage converted.

44. A method of driving a light emitting device that has a plurality of pixels each including a light emitting device,

wherein, in a first period, a current determined by a video signal is supplied to the pixels, and first means of each of the pixels converts the supplied current into a voltage to supply a first current to the light emitting element in an amount according to the voltage converted, and

wherein, in a second period, the first means of each of the pixels supplies a third current to the light emitting element in an amount according to the voltage converted, and second means of each of the pixels supplies a second current to the light emitting element in an amount according to the voltage converted.

45. A method of driving a light emitting device with one frame period having a first period and a second period,

wherein, in the first and second periods, a first transistor and second transistor of the light emitting device are connected to each other at their gates and a constant voltage is applied to sources of the first and second transistors,

wherein, in the first period, the gate of the first transistor is connected to a drain of the first transistor and a drain of the second transistor is connected to a pixel electrode of a light emitting element, and

wherein, in the second period, the drains of the first and second transistors are connected to the pixel electrode of the light emitting element and the gate of the first transistor is disconnected from the drain of the first transistor.

48. A method of driving a light emitting device according to claim 45, wherein the amount of drain current of the first transistor is controlled in the first period to thereby control the luminance of the light emitting element in the second period.

51. A light emitting device according to claim 45, wherein the first transistor and the second transistor have the same polarity.

46. A method of driving a light emitting device with one frame period having a first period and a second period,

wherein, in the first and second periods, a first transistor and second transistor of the light emitting device are connected to each other at their gates, a source of the first transistor and a source of the second transistor are connected to each other, and a constant voltage is applied to a drain of the first transistor,

wherein, in the first period, a drain of the second transistor is set to a floating state, and the gate of the first transistor is connected to the drain of the first transistor, and

wherein, in the second period, the constant voltage is applied to the drain of the second transistor, the gate of the first transistor is disconnected from the drain of the first transistor, and the sources of the first and second transistors are connected to a pixel electrode of a light emitting element.

49. A method of driving a light emitting device according to claim 46, wherein the amount of drain current of the first transistor is controlled in the first period to thereby control the luminance of the light emitting element in the second period.

52. A light emitting device according to claim 46, wherein the first transistor and the second transistor have the same polarity.

47. A method of driving a light emitting device with one frame period having a first period and a second period,

wherein, in the first and second periods, a first transistor and second transistor of the light emitting device are connected to each other at their gates, a drain of the first transistor and a drain of the second transistor are connected to each other, and a constant voltage is applied to the drains of the first and second transistors,

wherein, in the first period, the gates of the first and second transistors are connected to the drains of the first and second transistors, and

wherein, in the second period, sources of the first and second transistors are connected to a pixel electrode of a light emitting element.

50. A method of driving a light emitting device according to claim 47, wherein the amount of drain current of the first transistor is controlled in the first period to thereby control the luminance of the light emitting element in the second period.

53. A light emitting device according to claim 47, wherein the first transistor and the second transistor have the same polarity.

54. A method of driving a light emitting device with one frame period having a first period and a second period,

wherein, in the first and second periods, a first transistor and second transistor of the light emitting device are connected to each other at their gates, and a source of the first transistor and a source of the second transistor are connected to each other,

wherein, in the first period, a constant voltage is applied to the gate and drain of the first transistor, a drain of the second transistor is set to a floating state, and a drain current of the first transistor is controlled by a constant current source, and

wherein, in the second period, the gate of the first transistor is disconnected from the drain of the first transistor, a constant voltage is applied to the drains of the first and second transistors, and a drain current of the first transistor and a drain current of the second transistor both flow into a light emitting element.

55. A method of driving a light emitting device with one frame period having a first period and a second period,

wherein, in the first and second periods, a first transistor and second transistor of the light emitting device are connected to each other at their gates, and a drain of the first transistor and a drain of the second transistor are connected to each other,

wherein, in the first period, a constant voltage is applied to the gates of the first and second transistors and to the drains of the first and second transistors, and a drain current of the first transistor is controlled by a constant current source, and

wherein, in the second period, the gate of the first transistor is disconnected from the drain of the first transistor, the gate of the second transistor is disconnected from the drain of the second transistor, a constant voltage is applied to the drains of the first and second transistors, and a drain current of the first transistor and a drain current of the second transistor both flow into a light emitting element.

56. A method of driving a light emitting device with one frame period having a first period and a second period,

wherein, in the first and second periods, a first transistor and second transistor of the light emitting device are connected to each other at their gates, and a constant voltage is applied to sources of the first and second transistors,

wherein, in the first period, the gate of the first transistor is connected to a drain of the first transistor, a drain of the second transistor is connected to a pixel electrode of a light emitting element, and a drain current of the first transistor is controlled by a constant current source, and

wherein, in the second period, the gates of the first and second transistors are connected to a gate of a third transistor of the light emitting device, the first transistor and the third transistor have the same amount of drain current, and a drain current of the second transistor and a drain current of the third transistor both flow into the light emitting element.

57. A method of driving a light emitting device with one frame period having a first period and a second period,

wherein, in the first and second periods, a first transistor and second transistor of the light emitting device are connected to each other at their gates, and a source of the first transistor and a source of the second transistor are both connected to a pixel electrode of a light emitting element,

wherein, in the first period, the gate of the first transistor is connected to a drain of the first transistor, a constant voltage is applied to a drain of the second transistor, and a drain current of the first transistor is controlled by a constant current source, and

wherein, in the second period, the gates of the first and second transistors are connected to a gate of a third transistor of the light emitting device, the drain of the first transistor is connected to a source of the third transistor, a constant voltage is applied to a drain of the third transistor and to the drain of the second transistor, and a drain current of the second transistor and a drain current of the third transistor both flow into the light emitting element.

58. A method of driving a light emitting device that has a plurality of pixels each including a light emitting element,

wherein, in a first period, a current determined by a video signal is supplied to the pixels, and first means and second means of each of the pixels convert the supplied current into a voltage, and

wherein, in a second period, the second means of each of the pixels supplies a current to the light emitting element in an amount according to the voltage converted.

59. An element substrate having a plurality of pixels,

wherein each of the pixels has means for converting a supplied current into a voltage and for supplying a first current to a light emitting element in an amount according to the voltage converted, and has means for supplying a second current to the light emitting element in an amount according to the voltage converted.

60. An element substrate having a plurality of pixels and means for supplying a current to the pixels in an amount determined by a video signal,

wherein each of the pixels has means for converting the supplied current into a voltage and for supplying a first current to a light emitting element in an amount according to the voltage converted, and has means for supplying a second current to the light emitting element in an amount according to the voltage converted.

61. An element substrate having a plurality of pixels,

wherein each of the pixels has first and second means for converting the supplied current into a voltage, and

wherein the second means supplies a current to a light emitting element in an amount according to the voltage converted.

62. An element substrate having a plurality of pixels and means for supplying a current to the pixels in an amount determined by a video signal,

wherein each of the pixels has first and second means for converting the supplied current into a voltage, and

wherein the second means supplies a current to a light emitting element in an amount according to the voltage converted.