Light emitting device and method of driving the same

• US 20030057895A1
• Filed: 09/05/2002
• Published: 03/27/2003
• Est. Priority Date: 09/07/2001
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Kimura, Hajime
• Granted Patent: US 7,088,052 B2
• Time in Patent Office: Days
• US Class Current: 315/370
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2320/02 Improving the quality of display appearance
• CPC Class Codes: G09G 2320/0257 Reduction of after-image effects
• CPC Class Codes: G09G 2320/0285 using tables for spatial correction of display data
• 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 2320/0295 by monitoring each display pixel
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2340/14 Solving problems related to the presentation of information to be displayed
• CPC Class Codes: G09G 3/2059 using error diffusion
• CPC Class Codes: G09G 3/22 using controlled light sources
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• 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

Abstract

The present invention specifies the characteristic of a driving transistor provided in a pixel and corrects a video signal to be inputted to the pixel based on the specification. As a result, a light emitting device and its driving method in which influence of fluctuation in characteristic among transistors is removed to obtain clear multi-gray scale are provided. The present invention can also provide a light emitting device and its driving method in which a change with age in amount of current flowing between two electrodes of a light emitting element is reduced to obtain clear multi-gray scale display.

Claims

1. A light emitting device including a display panel with pixels each including a light emitting element, comprising:

memory means for storing an interpolation function for each of the pixels; and

signal correcting means for correcting a video signal using the interpolation function and an interpolation expression, Q=F(P).

7. A light emitting device as claimed in claim 1,

wherein the signal correcting means is a CPU or a microcomputer.

13. A light emitting device as claimed in claim 1,

wherein the memory means is selected from the group consisting of a semiconductor memory and a magnetic memory.

19. A light emitting device as claimed in claim 1,

wherein a transistor connected to the light emitting element and operating in a saturation range is placed in each of the pixels, and

wherein fluctuation in characteristic of the transistor is corrected.

25. A light emitting device as claimed in claim 1,

wherein a transistor connected to the light emitting element and operating in a linear range is placed in each of the pixels, and

wherein degradation of the light emitting element is corrected.

31. A light emitting device as claimed in claim 1,

wherein each of the pixels further comprises:

a first semiconductor element controlling a current flowing between two electrodes of the light emitting element;

a second semiconductor element controlling input of video signals to the pixels; and

a capacitor element holding the video signals.

37. A light emitting device as claimed in claim 1,

wherein each of the pixels further comprises:

a first semiconductor element controlling a current flowing between two electrodes of the light emitting element;

a second semiconductor element controlling input of video signals to the pixels;

a capacitor element holding the video signals; and

a third semiconductor element discharging electric charges held in the capacitor element.

64. A light emitting device as claimed in any one of claims 1,

wherein the interpolation expression Q=F(P) is expressed as Q=A*(P−

B)², Q=a*P+b, a spline function, a Bezier function, or a linear function.

2. A light emitting device including a display panel with pixels each including a light emitting element, comprising:

current measuring means for measuring the current value of the pixels;

calculating means for calculating an interpolation function for each of the pixels;

memory means for storing the interpolation function; and

signal correcting means for correcting a video signal using the interpolation function and an interpolation expression, Q=F(P).

8. A light emitting device as claimed in claims 2,

wherein the signal correcting means is a CPU or a microcomputer.

14. A light emitting device as claimed in claim 2,

wherein the memory means is selected from the group consisting of a semiconductor memory and a magnetic memory.

20. A light emitting device as claimed in claim 2,

wherein a transistor connected to the light emitting element and operating in a saturation range is placed in each of the pixels, and

wherein fluctuation in characteristic of the transistor is corrected.

26. A light emitting device as claimed in claim 2,

wherein a transistor connected to the light emitting element and operating in a linear range is placed in each of the pixels, and

wherein degradation of the light emitting element is corrected.

32. A light emitting device as claimed in claim 2,

wherein each of the pixels further comprises:

a first semiconductor element controlling a current flowing between two electrodes of the light emitting element;

a second semiconductor element controlling input of video signals to the pixels; and

a capacitor element holding the video signals.

38. A light emitting device as claimed in claim 2,

wherein each of the pixels further comprises:

a first semiconductor element controlling a current flowing between two electrodes of the light emitting element;

a second semiconductor element controlling input of video signals to the pixels;

a capacitor element holding the video signals; and

a third semiconductor element discharging electric charges held in the capacitor element.

43. A light emitting device as claimed in claim 2,

wherein the current measuring means measures current values I₁, I₂, . . . , I_n of when video signals P₁, P₂, . . . , P_n (n is a natural number at least equal to or larger than 2) are inputted to the pixels.

46. A light emitting device as claimed in claim 2,

wherein the current measuring means measures a current value I₀ of when every pixel in the display panel is not lit and a current value I₁, I₂, . . . , I_n (n is a natural number at least equal to or larger than 2) of when only one pixel in the display panel is lit.

49. A light emitting device as claimed in claim 2,

wherein the current measuring means measures a current value I₀ of when every pixel in the display panel is not lit and current values I₁, I₂, . . . , I_n (n is a natural number at least equal to or larger than 2) of when only one pixel in the display panel is lit, and

wherein the calculating means calculates the differences Q₁, Q₂, . . . , Q_n between the current values I₁, I₂, . . . , I_n and the current value I₀.

52. A light emitting device as claimed in claim 2,

wherein the current measuring means measures current values I₁, I₂, . . . , I_n of when video signals P₁, P₂, . . . , P_n (n is a natural number at least equal to or larger than 2) are inputted to the pixels and only one pixel in the display panel is lit as well as a current value I₀ of when every pixel in the display panel is not lit, and

wherein the calculating means calculates an interpolation function F using the differences Q1, Q2, . . . Qn between the current values I₁, I₂, . . . , I_n and the current value I₀ the video signals P₁, P₂, . . . , P_n, and an interpolation expression, Q=F(P).

55. A light emitting device as claimed in claim 2,

wherein the calculating means calculates an interpolation function F using video signals P₁, P₂, . . . , P_n (n is a natural number) inputted to the pixels, current values Q₁, Q₂, . . . , Q_n outputted from the current measuring means, and an interpolation expression, Q=F(P).

58. A light emitting device as claimed in claim 2,

wherein a given measurement operation is carried out by the current measuring means immediately before or after an image is displayed on the display panel, or before an interpolation function is stored in the memory means.

61. A light emitting device as claimed in claim 2,

wherein the calculating means is a CPU or a microcomputer.

65. A light emitting device as claimed in any one of claims 2,

wherein the interpolation expression Q=F(P) is expressed as Q=A*(P−

B)², Q=a*P+b, a spline function, a Bezier function, or a linear function.

3. A light emitting device for constituting a display panel with pixels each including a light emitting element, comprising:

memory means for storing an interpolation function for each of the pixels; and

signal correcting means for correcting a video signal using the interpolation function and an interpolation expression, Q=F(P).

9. A light emitting device as claimed in claim 3,

wherein the signal correcting means is a CPU or a microcomputer.

15. A light emitting device as claimed in claim 3,

wherein the memory means is selected from the group consisting of a semiconductor memory and a magnetic memory.

21. A light emitting device as claimed in claim 3,

wherein a transistor connected to the light emitting element and operating in a saturation range is placed in each of the pixels, and

wherein fluctuation in characteristic of the transistor is corrected.

27. A light emitting device as claimed in claim 3,

wherein a transistor connected to the light emitting element and operating in a linear range is placed in each of the pixels, and

wherein degradation of the light emitting element is corrected.

33. A light emitting device as claimed in claim 3,

wherein each of the pixels further comprises:

a first semiconductor element controlling a current flowing between two electrodes of the light emitting element;

a second semiconductor element controlling input of video signals to the pixels; and

a capacitor element holding the video signals.

39. A light emitting device as claimed in claim 3,

wherein each of the pixels further comprises:

a first semiconductor element controlling a current flowing between two electrodes of the light emitting element;

a second semiconductor element controlling input of video signals to the pixels;

a capacitor element holding the video signals; and

a third semiconductor element discharging electric charges held in the capacitor element.

66. A light emitting device as claimed in any one of claims 3,

wherein the interpolation expression Q=F(P) is expressed as Q=A*(P−

B)², Q=a*P+b, a spline function, a Bezier function, or a linear function.

4. A light emitting device for constituting a display panel with pixels each including a light emitting element, comprising:

current measuring means for measuring the current value of the pixels;

calculating means for calculating an interpolation function for each of the pixels;

memory means for storing the interpolation function; and

signal correcting means for correcting a video signal using the interpolation function and an interpolation expression, Q=F(P).

10. A light emitting device as claimed in claim 4,

wherein the signal correcting means is a CPU or a microcomputer.

16. A light emitting device as claimed in any one of claims 4,

wherein the memory means is selected from the group consisting of a semiconductor memory and a magnetic memory.

22. A light emitting device as claimed in claim 4,

wherein a transistor connected to the light emitting element and operating in a saturation range is placed in each of the pixels, and

wherein fluctuation in characteristic of the transistor is corrected.

28. A light emitting device as claimed in claim 4,

wherein a transistor connected to the light emitting element and operating in a linear range is placed in each of the pixels, and

wherein degradation of the light emitting element is corrected.

34. A light emitting device as claimed in claim 4,

wherein each of the pixels further comprises:

a first semiconductor element controlling a current flowing between two electrodes of the light emitting element;

a second semiconductor element controlling input of video signals to the pixels; and

a capacitor element holding the video signals.

40. A light emitting device as claimed in claim 4,

wherein each of the pixels further comprises:

a first semiconductor element controlling a current flowing between two electrodes of the light emitting element;

a second semiconductor element controlling input of video signals to the pixels;

a capacitor element holding the video signals; and

a third semiconductor element discharging electric charges held in the capacitor element.

44. A light emitting device as claimed in claim 4,

wherein the current measuring means measures current values I₁, I₂, . . . , I_n of when video signals P₁, P₂, . . . , P_n (n is a natural number at least equal to or larger than 2) are inputted to the pixels.

47. A light emitting device as claimed in claim 4,

wherein the current measuring means measures a current value I₀ of when every pixel in the display panel is not lit and a current value I₁, I₂, . . . , I_n (n is a natural number at least equal to or larger than 2) of when only one pixel in the display panel is lit.

50. A light emitting device as claimed in claim 4,

wherein the current measuring means measures a current value I₀ of when every pixel in the display panel is not lit and current values I₁, I₂, . . . , I_n (n is a natural number at least equal to or larger than 2) of when only one pixel in the display panel is lit, and

wherein the calculating means calculates the differences Q₁, Q₂, . . . , Q_n between the current values I₁ , I₂, . . . , I_n and the current value I₀.

53. A light emitting device as claimed in claim 4,

wherein the current measuring means measures current values I₁, I₂, . . . , I_n of when video signals P₁, P₂, . . . , P_n (n is a natural number at least equal to or larger than 2) are inputted to the pixels and only one pixel in the display panel is lit as well as a current value I₀ of when every pixel in the display panel is not lit, and

wherein the calculating means calculates an interpolation function F using the differences Q1, Q2, . . . Qn between the current values I₁, I₂, . . . , I_n and the current value I₀, the video signals P₁, P₂ . . . , P_n, and an interpolation expression, Q=F(P).

56. A light emitting device as claimed in claim 4,

wherein the calculating means calculates an interpolation function F using video signals P₁, P₂, . . . , P_n (n is a natural number) inputted to the pixels, current values Q₁, Q₂, . . . , Q_n outputted from the current measuring means, and an interpolation expression, Q=F(P).

59. A light emitting device as claimed in claim 4,

wherein a given measurement operation is carried out by the current measuring means immediately before or after an image is displayed on the display panel, or before an interpolation function is stored in the memory means.

62. A light emitting device as claimed in claim 4,

wherein the calculating means is a CPU or a microcomputer.

67. A light emitting device as claimed in any one of claims 4,

wherein the interpolation expression Q=F(P) is expressed as Q=A*(P−

B)², Q=a*P+b, a spline function, a Bezier function, or a linear function.

5. A light emitting device for constituting memory means and signal correcting means,

wherein the device comprises a display panel with pixels each including a light emitting element, and

wherein the memory means stores an interpolation function for each of the pixels of the display panel, and the signal correcting means corrects a video signal using the interpolation function that is stored in the memory means and an interpolation expression, Q=F(P).

11. A light emitting device as claimed in claim 5,

wherein the signal correcting means is a CPU or a microcomputer.

17. A light emitting device as claimed in claim 5,

wherein the memory means is selected from the group consisting of a semiconductor memory and a magnetic memory.

23. A light emitting device as claimed in claim 5,

wherein a transistor connected to the light emitting element and operating in a saturation range is placed in each of the pixels, and

wherein fluctuation in characteristic of the transistor is corrected.

29. A light emitting device as claimed in claim 5,

wherein a transistor connected to the light emitting element and operating in a linear range is placed in each of the pixels, and

wherein degradation of the light emitting element is corrected.

35. A light emitting device as claimed in claim 5,

wherein each of the pixels further comprises:

a first semiconductor element controlling a current flowing between two electrodes of the light emitting element;

a second semiconductor element controlling input of video signals to the pixels; and

a capacitor element holding the video signals.

41. A light emitting device as claimed in claim 5,

wherein each of the pixels further comprises:

a first semiconductor element controlling a current flowing between two electrodes of the light emitting element;

a second semiconductor element controlling input of video signals to the pixels;

a capacitor element holding the video signals; and

a third semiconductor element discharging electric charges held in the capacitor element.

68. A light emitting device as claimed in any one of claims 5,

wherein the interpolation expression Q=F(P) is expressed as Q=A*(P−

B)², Q=a*P+b, a spline function, a Bezier function, or a linear function.

6. A light emitting device for constituting current measuring means, calculating means, memory means, and signal correcting means,

wherein the device comprises a display panel with pixels each including a light emitting element, and

wherein the current measuring means measures the current value of the pixels, the calculating means calculates an interpolation function for each of the pixels using an output of the current measuring means, the memory means stores the interpolation function, and the signal correcting means corrects a video signal using the interpolation function that is stored in the memory means and an interpolation expression, Q=F(P).

12. A light emitting device as claimed in claim 6,

wherein the signal correcting means is a CPU or a microcomputer.

18. A light emitting device as claimed in claim 6,

wherein the memory means is selected from the group consisting of a semiconductor memory and a magnetic memory.

24. A light emitting device as claimed in claim 6,

wherein a transistor connected to the light emitting element and operating in a saturation range is placed in each of the pixels, and

wherein fluctuation in characteristic of the transistor is corrected.

30. A light emitting device as claimed in claim 6,

wherein a transistor connected to the light emitting element and operating in a linear range is placed in each of the pixels, and

wherein degradation of the light emitting element is corrected.

36. A light emitting device as claimed in claim 6,

wherein each of the pixels further comprises:

a first semiconductor element controlling a current flowing between two electrodes of the light emitting element;

a second semiconductor element controlling input of video signals to the pixels; and

a capacitor element holding the video signals.

42. A light emitting device as claimed in claim 6,

wherein each of the pixels further comprises:

a first semiconductor element controlling a current flowing between two electrodes of the light emitting element;

a second semiconductor element controlling input of video signals to the pixels;

a capacitor element holding the video signals; and

a third semiconductor element discharging electric charges held in the capacitor element.

45. A light emitting device as claimed in claim 6,

wherein the current measuring means measures current values I₁, I₂, . . . , I_n of when video signals P₁, P₂, . . . , P_n (n is a natural number at least equal to or larger than 2) are inputted to the pixels.

48. A light emitting device as claimed in claim 6,

wherein the current measuring means measures a current value I₀ of when every pixel in the display panel is not lit and a current value I₁, I₂, . . . , I_n (n is a natural number at least equal to or larger than 2) of when only one pixel in the display panel is lit.

51. A light emitting device as claimed in claim 6,

wherein the current measuring means measures a current value I₀ of when every pixel in the display panel is not lit and current values I₁, I₂, . . . , I_n (n is a natural number at least equal to or larger than 2) of when only one pixel in the display panel is lit, and

wherein the calculating means calculates the differences Q₁, Q₂, . . . , Q_n between the current values I₁, I₂, . . . , I_n and the current value I₀.

54. A light emitting device as claimed in claim 6,

wherein the current measuring means measures current values I₁, I₂, . . . , I_n of when video signals P₁, P₂, . . . , P_n (n is a natural number at least equal to or larger than 2) are inputted to the pixels and only one pixel in the display panel is lit as well as a current value I₀ of when every pixel in the display panel is not lit, and

wherein the calculating means calculates an interpolation function F using the differences Q1, Q2, . . . Qn between the current values I₁, I₂, . . . , I_n and the current value I₀ the video signals P₁, P₂, . . . , P_n, and an interpolation expression, Q=F(P).

57. A light emitting device as claimed in claim 6,

wherein the calculating means calculates an interpolation function F using video signals P₁, P₂ . . . , P_n (n is a natural number) inputted to the pixels, current values Q₁, Q₂, . . . Q_n outputted from the current measuring means, and an interpolation expression, Q=F(P).

60. A light emitting device as claimed in claim 6,

wherein a given measurement operation is carried out by the current measuring means immediately before or after an image is displayed on the display panel, or before an interpolation function is stored in the memory means.

63. A light emitting device as claimed in claim 6,

wherein the calculating means is a CPU or a microcomputer.

69. A light emitting device as claimed in any one of claims 6,

wherein the interpolation expression Q=F(P) is expressed as Q=A*(P−

B)², Q=a*P+b, a spline function, a Bezier function, or a linear function.

70. A method of driving a light emitting device having a display panel, comprising:

measuring a current value I₀ of when every pixel in the display panel is not lit;

measuring current values I₁, I₂, . . . , I_n of when only one pixel in the display panel is lit; and

correcting video signals inputted to pixels of the display panel using the differences Q₁, Q₂, . . . , Q_n between the current value I₀ and the current values I₁, I₂,. . . , I_n, and the video signals P₁, P₂, . . . , P_n.

71. A method of driving a light emitting device having a display panel, comprising:

measuring a current value I₀ of when every pixel in the display panel is not lit;

measuring current values I₁, I₂, . . . , I_n of when only one pixel in the display panel is lit; and

correcting video signals inputted to pixels of the display panel using the differences Q₁, Q₂, . . . Q_n between the current value I₀ and the current values I₁, I₂, . . . , I_n, and the video signals P₁, P₂, . . . , P_n.

72. A method of driving a light emitting device having a display panel, comprising:

measuring a current value I₀ of when every pixel in the display panel is not lit;

measuring current values I₁ , I₂, . . . , I_n of when only one pixel in the display panel is lit;

calculating an interpolation function F using the differences Q₁, Q₂, . . . Q_n between the current value I₀ and the current values I₁, I₂, . . . I_n, the video signals P₁, P₂, . . . , P_n, and an interpolation expression, Q=F(P); and

correcting video signals inputted to pixels of the display panel using the interpolation function F.