Display device

• US 6,528,951 B2
• Filed: 06/12/2001
• Issued: 03/04/2003
• Est. Priority Date: 06/13/2000
• Status: Expired due to Term

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Koyama, Jun, Yamazaki, Shunpei, Hosoki, Kazue
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Lee, Wilson
• Application Number:
  US09/878,312
• Publication Number:
  US 20020005696A1
• Time in Patent Office: 630 Days
• Field of Search: 315/167, 315/168, 315/169--16, 313/495, 345/76, 345/77, 257/40, 257/57, 257/59
• US Class Current: 315/169.3
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• CPC Class Codes: G09G 2320/041 Temperature compensation
• 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 3/2022 using sub-frames
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

The image quality of a display device using a bottom gate TFT is improved. In particular, fluctuation in luminance is controlled and the frequency characteristic of a driver circuit is compensated by suppressing a change in amount of current flowing through an EL element which is caused by a change in surrounding temperature while the device is in use. A monitoring EL element is provided in addition to a pixel portion EL element. The monitoring EL element constitutes a temperature compensation circuit together with a buffer amplifier and the like. A current is supplied to the pixel portion EL element through the temperature compensation circuit. This makes it possible to keep the amount of current flowing through the pixel portion EL element constant against a change in temperature, and to control the fluctuation in luminance. An input signal is subjected to time base expansion to perform sampling with accuracy.

Claims

1. A display device comprising a buffer amplifier, a monitoring EL element, a constant current generator, a plurality of pixels and a power supply line, wherein

each of said plurality of pixels has a bottom-gate type TFT and an EL element;

each of said monitoring EL element and said EL element has a first electrode, a second electrode and an EL layer interposed between said first electrode and said second electrode;

said first electrode of said monitoring EL element is connected to said constant current generator and a non-inversed input terminal of said buffer amplifier;

an output terminal of said buffer amplifier is connected to said constant current generator, and

an electric potential of said power supply line is provided to said first electrode of said EL element though said bottom-gate type TFT.

10. A display device according to claim 1, wherein said first electrode is an anode and said second electrode is a cathode in both of said monitoring EL element and said EL element.

11. A display device according to claim 1, wherein said first electrode is a cathode and said second electrode is an anode in both of said monitoring EL element and said EL element.

12. A display device according to claim 1, wherein at least one of said buffer amplifier and said constant current generator is composed of a thin film transistor.

14. A display device according to claim 1, wherein said EL element has an EL layer emitting monochrome light and color conversion layers in combination to provide color display.

15. A display device according to claim 1, wherein said EL element has an EL layer emitting white light and color filters in combination to provide color display.

16. A display device according to claim 1, wherein said EL layer of said EL element is formed from a low molecular weight organic material or a polymer organic material.

17. A display device according to claim 16, wherein said low molecular weight organic material contains Alq₃ (tris-8-quinolilite-aluminum) or TPD (triphenylamine derivative).

18. A display device according to claim 16, wherein said polymer organic material contains PPV (polyphenylene vinylene), PVK (polyvinyl carbazole) or polycarbonate.

19. A display device according to claim 1, wherein said EL layer of said EL element is formed from an inorganic material.

20. A display device according to claim 1, wherein said display device is incorporated into an electronic equipment selected from the group consisting of a personal computer, a video camera, a head mounted display, an image play back device, and a mobile computer.

2. A display device comprising a buffer amplifier, a monitoring EL element, a constant current generator, an adder circuit, a plurality of pixels and a power supply line, wherein:

each of said plurality of pixels has a bottom-gate type TFT and an EL element;

each of said monitoring EL element and said EL element has a first electrode, a second electrode and an EL layer interposed between said first electrode and said second electrode;

said first electrode of said monitoring EL element is connected to said constant current generator and a non-inversed input terminal of said buffer amplifier;

an output terminal of said buffer amplifier is connected to an input terminal of said adder circuit,

an output terminal of said adder circuit is connected to said power supply line;

the difference in electric potential between said input terminal of said adder circuit and said output terminal thereof is kept constant; and

the electric potential of said power supply line is provided to said first electrode of said EL element though said bottom-gate type TFT.

13. A display device according to claim 2, wherein at least one of said buffer amplifier, said constant current generator and said adder circuit is composed of a thin film transistor.

29. A display device according to claim 2, wherein said first electrode is an anode and said second electrode is a cathode in both of said monitoring EL element and said EL element.

33. A display device according to claim 2, wherein said first electrode is a cathode and said second electrode is an anode in both of said monitoring EL element and said EL element.

37. A display device according to claim 2, wherein at least one of said buffer amplifier and said constant current generator is composed of a thin film transistor.

43. A display device according to claim 2, wherein said EL element has an EL layer emitting monochrome light and color conversion layers in combination to provide color display.

47. A display device according to claim 2, wherein said EL element has an EL layer emitting white light and color filters in combination to provide color display.

51. A display device according to claim 2, wherein said EL layer of said EL element is formed from a low molecular weight organic material or a polymer organic material.

56. A display device according to claim 2, wherein said EL layer of said EL element is formed from an inorganic material.

60. A display device according to claim 2, wherein said display device is incorporated into an electronic equipment selected from the group consisting of a personal computer, a video camera, a head mounted display, an image play back device, and a mobile computer.

3. A display device comprising:

a monitoring EL element;

a plurality of source signal lines;

a plurality of gate signal lines;

a plurality of power supply lines;

a plurality of pixels;

a source signal line driving circuit for inputting a signal into said plurality of source signal lines; and

a gate signal line driving circuit for inputting a signal to said plurality of gate signal lines,

wherein;

each of said plurality of pixels has an EL element, a switching TFT, and a driving TFT;

each of said monitoring EL element and said EL element has a first electrode, a second electrode, and an EL layer interposed between said first electrode and said second electrode;

a gate electrode of said switching TFT is connected to one of said plurality of gate signal lines;

one of a source region and a drain region of said switching TFT is connected to one of said plurality of source signal lines, and the other of which is connected to a gate electrode of said driving TFT;

one of a source region and a drain region of said driving TFT is connected to one of said plurality of power supply lines, and the other one of which is connected to one of said first electrode and said second electrode of said EL element; and

said monitoring EL element is used to reduce a change in amount of current flowing from one of said plural power supply lines into said EL element due to a temperature change.

6. A display device according to claim 3 wherein said source signal line driving circuit has means for successively sampling digital signals.

7. A display device according to claim 3, wherein said source signal line driving circuit has means for successively sampling digital signals that have been subjected to k-fold time expansion (k is a natural number), the sampling being perform ed simultaneously on k digital signals.

8. A display device according to claim 3, wherein said source signal line driving circuit has means for successively sampling analog signals.

9. A display device according to claim 3, wherein said source signal line driving circuit has means for successively sampling analog signals that have been subjected to k- fold time expansion (k is a natural number), the sampling being performed simultaneously on k analog signals.

30. A display device according to claim 3, wherein said first electrode is an anode and said second electrode is a cathode in both of said monitoring EL element and said EL element.

34. A display device according to claim 3, wherein said first electrode is a cathode and said second electrode is an anode in both of said monitoring EL element and said EL element.

38. A display device according to claim 3, wherein at least one of said buffer amplifier and said constant current generator is composed of a thin film transistor.

40. A display device according to claim 3, wherein at least one of said buffer amplifier, said constant current generator and said adder circuit is composed of a thin film transistor.

44. A display device according to claim 3, wherein said EL element has an EL layer emitting monochrome light and color conversion layers in combination to provide color display.

48. A display device according to claim 3, wherein said EL element has an EL layer emitting white light and color filters in combination to provide color display.

52. A display device according to claim 3, wherein said EL layer of said EL element is formed from a low molecular weight organic material or a polymer organic material.

57. A display device according to claim 3, wherein said EL layer of said EL element is formed from an inorganic material.

61. A display device according to claim 3, wherein said display device is incorporated into an electronic equipment selected from the group consisting of a personal computer, a video camera, a head mounted display, an image play back device, and a mobile computer.

4. A display device comprising:

a monitoring EL element;

a buffer amplifier;

a constant current generator;

a plurality of source signal lines;

a plurality of gate signal lines;

a plurality of power supply lines;

a plurality of pixels;

a source signal line driving circuit for inputting a signal into said plurality of source signal lines; and

a gate signal line driving circuit for inputting a signal to said plurality of gate signal lines,

wherein;

each of said plurality of pixels has an EL element, a switching TFT and a driving TFT;

said source signal line driving circuit has a bottom-gate type TFT;

each of said monitoring EL element and said EL element has a first electrode, a second electrode, and an EL layer interposed between said first electrode and said second electrode;

a gate electrode of said switching TFT is connected to one of said plurality of gate signal lines;

one of a source region and a drain region of said switching TFT is connected to one of said plurality of source signal lines, and the other of which is connected to a gate electrode of said driving TFT;

one of a source region and a drain region of said driving TFT is connected to one of said plurality of power supply lines, and the other one of which is connected to said first electrode of said EL element; and

a first electrode of said monitoring EL element is connected to said constant current generator and an non-inversed input terminal of said buffer amplifier;

an output terminal of said buffer amplifier is connected to said plurality of power supply lines, and

the electric potential of said plurality of power supply lines is provided to said first electrode of said EL element though said bottom-gate type TFT of said driving TFT.

21. A display device according to claim 4 wherein said source signal line driving circuit has means for successively sampling digital signals.

23. A display device according to claim 4, wherein said source signal line driving circuit has means for successively sampling digital signals that have been subjected to k-fold time expansion (k is a natural number), the sampling being perform ed simultaneously on k digital signals.

25. A display device according to claim 4, wherein said source signal line driving circuit has means for successively sampling analog signals.

27. A display device according to claim 4, wherein said source signal line driving circuit has means for successively sampling analog signals that have been subjected to k-fold time expansion (k is a natural number), the sampling being performed simultaneously on k analog signals.

31. A display device according to claim 4, wherein said first electrode is an anode and said second electrode is a cathode in both of said monitoring EL element and said EL element.

35. A display device according to claim 4, wherein said first electrode is a cathode and said second electrode is an anode in both of said monitoring EL element and said EL element.

39. A display device according to claim 4, wherein at least one of said buffer amplifier and said constant current generator is composed of a thin film transistor.

41. A display device according to claim 4, wherein at least one of said buffer amplifier, said constant current generator and said adder circuit is composed of a thin film transistor.

45. A display device according to claim 4, wherein said EL element has an EL layer emitting monochrome light and color conversion layers in combination to provide color display.

49. A display device according to claim 4, wherein said EL element has an EL layer emitting white light and color filters in combination to provide color display.

53. A display device according to claim 4, wherein said EL layer of said EL element is formed from a low molecular weight organic material or a polymer organic material.

58. A display device according to claim 4, wherein said EL layer of said EL element is formed from an inorganic material.

62. A display device according to claim 4, wherein said display device is incorporated into an electronic equipment selected from the group consisting of a personal computer, a video camera, a head mounted display, an image play back device, and a mobile computer.

5. A display device comprising:

a monitoring EL element;

a buffer amplifier;

a constant current generator;

an adder circuit;

a plurality of source signal lines;

a plurality of gate signal lines;

a plurality of power supply lines;

a plurality of pixels;

a source signal line driving circuit for inputting a signal into said plurality of source signal lines; and

a gate signal line driving circuit for inputting a signal to said plurality of gate signal lines,

wherein;

said source signal line driving circuit has a bottom-gate type TFT,

each of said plurality of pixels has an EL element, a switching TFT, and a driving TFT;

each of said monitoring EL element and said EL element has a first electrode, a second electrode, and an EL layer interposed between said first electrode and said second electrode;

a gate electrode of said switching TFT is connected to one of said plurality of gate signal lines;

one of a source region and a drain region of said switching TFT is connected to one of said plurality of source signal lines, and the other of which is connected to a gate electrode of said driving TFT,

one of a source region and a drain region of said driving TFT is connected to one of said plurality of power supply lines, and the other one of which is connected to said first electrode of said EL element;

said first electrode of said monitoring EL element is connected to said constant current generator and an non-inversion input terminal of said buffer amplifier;

an output terminal of said buffer amplifier is connected to an input terminal of said adder circuit;

an output terminal of said adder circuit is connected to one of said plurality of power supply lines;

the difference in electric potential between said input terminal of said adder circuit and said output terminal thereof is kept constant; and

the electric potential of said plurality of power supply line is provided to said first electrode of said EL element though said driving TFT.

22. A display device according to claim 5 wherein said source signal line driving circuit has means for successively sampling digital signals.

24. A display device according to claim 5, wherein said source signal line driving circuit has means for successively sampling digital signals that have been subjected to k-fold time expansion (k is a natural number), the sampling being perform ed simultaneously on k digital signals.

26. A display device according to claim 5, wherein said source signal line driving circuit has means for successively sampling analog signals.

28. A display device according to claim 5, wherein said source signal line driving circuit has means for successively sampling analog signals that have been subjected to k-fold time expansion (k is a natural number), the sampling being performed simultaneously on k analog signals.

32. A display device according to claim 5, wherein said first electrode is an anode and said second electrode is a cathode in both of said monitoring EL element and said EL element.

36. A display device according to claim 5, wherein said first electrode is a cathode and said second electrode is an anode in both of said monitoring EL element and said EL element.

42. A display device according to claim 5, wherein at least one of said buffer amplifier, said constant current generator and said adder circuit is composed of a thin film transistor.

46. A display device according to claim 5, wherein said EL element has an EL layer emitting monochrome light and color conversion layers in combination to provide color display.

50. A display device according to claim 5, wherein said EL element has an EL layer emitting white light and color filters in combination to provide color display.

54. A display device according to claim 5, wherein said display device is incorporated into an electronic equipment selected from the group consisting of a personal computer, a video camera, a head mounted display, an image play back device, and a mobile computer.

55. A display device according to claim 5, wherein said EL layer of said EL element is formed from a low molecular weight organic material or a polymer organic material.

59. A display device according to claim 5, wherein said EL layer of said EL element is formed from an inorganic material.