Light emitting device

• US 7,042,427 B2
• Filed: 01/23/2002
• Issued: 05/09/2006
• Est. Priority Date: 01/29/2001
• Status: Expired due to Fees

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Inukai, Kazutaka
• Primary Examiner(s): LAO, LUN YI
• Application Number:
  US10/057,657
• Publication Number:
  US 20020101395A1
• Time in Patent Office: 1,567 Days
• Field of Search: 345211-212, 345 77- 78, 345 82- 83, 315/169.3
• US Class Current: 345/77
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• 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 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2330/02 Details of power systems and of start or stop of display operation
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element
• CPC Class Codes: H10K 59/12 Active-matrix OLED [AMOLED] displays

Abstract

A light emitting device with a simple and easy structure without waste is provided, in which a change of luminance of an OLED is suppressed and a desired color display can be stably performed even if an organic light emitting layer is somewhat deteriorated or an environmental temperature is varied. A driving current of the OLED of a pixel portion is measured, and a value of the voltage supplied to the pixel portion from a variable power supply is corrected such that the measured driving current has a reference value. When the driving current of the OLED is measured, a monitor video signal of a different system from that of a video signal for displaying an image is used to display a monitor image on the pixel portion. With the above-described structure, a reduction of the luminance accompanied with the deterioration of the organic light emitting layer can be suppressed. As a result, a clear image can be displayed.

Claims

1. A light emitting device comprising:

a light emitting device comprising organic material;

means for measuring a current flowing between a first electrode and a second electrode of the light emitting device;

means for comparing the measured current value and a reference current value; and

means for correcting a voltage between the first electrode and the second electrode of the light emitting device for making the value of the current flowing between the first electrode and the second electrode of the light emitting device close to the reference current value based on a difference between the measured current value and the reference current value,

wherein the voltage to be corrected is changed with a constant size every time when the difference between the measured current value and the reference current value is changed with a constant width, and

wherein a specific image is displayed when the current flowing between the first electrode and the second electrode of the light emitting device is measured.

2. A device according to claim 1, wherein the measuring means, the comparing means, and the correcting means are provided for each of corresponding colors of the light emitting device.

3. A device according to claim 1, wherein a period during which the light emitting device emits light is controlled with a digital video signal to display gradations.

4. A device according to claim 1, wherein the comparing means comprises a calculation circuit.

5. A light emitting device comprising:

a plurality of pixels each having a light emitting device comprising organic material;

means for measuring the total of a current flowing between a first electrode and a second electrode of the light emitting devices provided in at least two of the plurality of pixels;

means for comparing the measured current value and a reference current value; and

means for correcting a voltage between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels for making the value of the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels close to the reference current value based on a difference between the measured current value and the reference current value,

wherein a specific image is displayed when the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels is measured, and

wherein the reference current value differs depending on an image displayed when the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels is measured.

6. A device according to claim 5, wherein the measuring means, the comparing means, and the correcting means are provided for each of corresponding colors of the light emitting devices.

7. A device according to claim 5, wherein a period during which the light emitting devices emits light is controlled with a digital video signal to display gradations.

8. A device according to claim 5, wherein the comparing means comprises a calculation circuit.

9. A light emitting device comprising:

a plurality of pixels each having a light emitting device comprising organic material;

means for measuring the total of a current flowing between a first electrode and a second electrode of the light emitting devices provided in at least two of the plurality of pixels;

means for comparing the measured current value and a reference current value; and

means for correcting a voltage between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels for making the value of the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels close to the reference current value based on a difference between the measured current value and the reference current value,

wherein the voltage to be corrected is changed with a constant size every time when the difference between the measured current value and the reference current value is changed with a constant width.

10. A device according to claim 9, wherein the measuring means, the comparing means, and the correcting means are provided for each of corresponding colors of the light emitting devices.

11. A device according to claim 9, wherein a period during which the light emitting device emits light is controlled with a digital video signal to display gradations.

12. A device according to claim 9, wherein the comparing means comprises a calculation circuit.

13. A light emitting device comprising:

a plurality of pixels each having a light emitting device comprising organic material in a pixel portion;

means for measuring the total of a current flowing between a first electrode and a second electrode of the light emitting devices provided in at least two of the plurality of pixels;

means for comparing the measured current value and a reference current value;

means for correcting a voltage between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels for making the value of the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels close to the reference current value based on a difference between the measured current value and the reference current value,

wherein the reference current value differs depending on an image displayed on the pixel portion when the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels is measured.

14. A device according to claim 13, wherein the measuring means, the comparing means, and the correcting means are provided for each of corresponding colors of the light emitting devices.

15. A device according to claim 13, wherein a period during which the light emitting device emits light is controlled with a digital video signal to display gradations.

16. A device according to claim 13, wherein the comparing means comprises a calculation circuit.

17. A light emitting device comprising:

a plurality of pixels each having a light emitting device comprising organic material in a pixel portion, the pixel portion being provided with at least two of the plurality of pixels each having a light emitting device and at least one TFT, and the TFT controlling light emission of the light emitting device;

means for measuring the total of a current flowing between a first electrode and a second electrode of the light emitting devices;

means for comparing the measured current value and a reference current value; and

means for correcting a voltage between the first electrode and the second electrode of the light emitting devices for making the value of the total of the current flowing between the first electrode and the second electrode of the light emitting devices close to the reference current value based on a difference between the measured current value and the reference current value,

wherein a specific image is displayed on the pixel portion when the total of the current flowing between the first electrode and the second electrode of the light emitting devices is measured, and

wherein the reference current value differs depending on an image displayed on the pixel portion when the total of the current flowing between the first electrode and the second electrode of the light emitting devices is measured.

18. A device according to claim 17, wherein the measuring means, the comparing means, and the correcting means are provided for each of corresponding colors of the light emitting devices.

19. A device according to claim 17, wherein a period during which the light emitting device emits light is controlled with a digital video signal to display gradations.

20. A device according to claim 17, wherein the comparing means comprises a calculation circuit.

21. A light emitting device comprising:

a light emitting device comprising organic material;

a variable power supply;

an ammeter for measuring a current flowing between a first electrode and a second electrode of the light emitting device; and

a correction circuit for comparing the measured current value and a reference current value and correcting a voltage between the first electrode and the second electrode of the light emitting device for making the value of the current flowing between the first electrode and the second electrode of the light emitting device close to the reference current value by controlling the variable power supply,

wherein the voltage to be corrected is changed with a constant size every time when the difference between the measured current value and the reference current value is changed with a constant width, and

wherein a specific image is displayed when the current flowing between the first electrode and the second electrode of the light emitting device is measured.

22. A device according to claim 21, wherein the variable power supply, the ammeter and the correction circuit are provided for each of corresponding colors of the light emitting device.

23. A device according to claim 21, wherein a second substrate on which the correction circuit or the ammeter is formed is attached onto a first substrate on which the light emitting device is formed.

24. A device according to claim 21, wherein a second substrate on which the correction circuit or the ammeter is formed is attached onto a first substrate on which the light emitting device is formed by a COG method.

25. A device according to claim 21, wherein a second substrate on which the correction circuit or the ammeter is formed is attached onto a first substrate on which the light emitting device is formed by a wire bonding method.

26. A device according to claim 21, wherein a period during which the light emitting device emits light is controlled with a digital video signal to display gradations.

27. A light emitting device comprising:

a plurality of pixels each having a light emitting device comprising organic material;

an ammeter for measuring the total of a current flowing between a first electrode and a second electrode of the light emitting devices provided in at least two of the plurality of pixels; and

a correction circuit for comparing the measured current value and a reference current value and correcting a voltage between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels for making the value of the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels close to the reference current value by controlling a variable power supply,

wherein a specific image is displayed when the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels is measured, and

wherein the reference current value differs depending on an image displayed when the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels is measured.

28. A device according to claim 27, wherein the variable power supply, the ammeter and the correction circuit are provided for each of corresponding colors of the light emitting device.

29. A device according to claim 27, wherein a second substrate on which the correction circuit or the ammeter is formed is attached onto a first substrate on which the light emitting device is formed.

30. A device according to claim 27, wherein a second substrate on which the correction circuit or the ammeter is formed is attached onto a first substrate on which the light emitting device is formed by a COG method.

31. A device according to claim 27, wherein a second substrate on which the correction circuit or the ammeter is formed is attached onto a first substrate on which the light emitting device is formed by a wire bonding method.

32. A device according to claim 27, wherein a period during which the light emitting device emits light is controlled with a digital video signal to display gradations.

33. A light emitting device comprising:

a plurality of pixels each having a light emitting device comprising organic material;

an ammeter for measuring the total of a current flowing between a first electrode and a second electrode of the light emitting devices provided in at least two of the plurality of pixels; and

a correction circuit for comparing the measured current value and a reference current value and correcting a voltage between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels for making the value of the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels close to the reference current value by controlling a variable power supply,

wherein the voltage to be corrected is changed with a constant size every time when the difference between the measured current value and the reference current value is changed with a constant width.

34. A device according to claim 33, wherein the variable power supply, the ammeter and the correction circuit are provided for each of corresponding colors of the light emitting device.

35. A device according to claim 33, wherein a second substrate on which the correction circuit or the ammeter is formed is attached onto a first substrate on which the light emitting device is formed.

36. A device according to claim 33, wherein a second substrate on which the correction circuit or the ammeter is formed is attached onto a first substrate on which the light emitting device is formed by a COG method.

37. A device according to claim 33, wherein a second substrate on which the correction circuit or the ammeter is formed is attached onto a first substrate on which the light emitting device is formed by a wire bonding method.

38. A device according to claim 33, wherein a period during which the light emitting device emits light is controlled with a digital video signal to display gradations.

39. A light emitting device comprising:

a plurality of pixels each having a light emitting device comprising organic material in a pixel portion;

an ammeter for measuring the total of a current flowing between a first electrode and a second electrode of the light emitting devices provided in at least two of the plurality of pixels; and

a correction circuit for comparing the measured current value and a reference current value and correcting a voltage between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels for making the value of the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels close to the reference current value by controlling a variable power supply,

wherein the reference current value differs depending on an image displayed on the pixel portion when the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels is measured.

40. A device according to claim 39, wherein the variable power supply, the ammeter and the correction circuit are provided for each of corresponding colors of the light emitting device.

41. A device according to claim 39, wherein a second substrate on which the correction circuit or the ammeter is formed is attached onto a first substrate on which the light emitting device is formed.

42. A device according to claim 39, wherein a second substrate on which the correction circuit or the ammeter is formed is attached onto a first substrate on which the light emitting device is formed by a COG method.

43. A device according to claim 39, wherein a second substrate on which the correction circuit or the ammeter is formed is attached onto a first substrate on which the light emitting device is formed by a wire bonding method.

44. A device according to claim 39, wherein a period during which the light emitting device emits light is controlled with a digital video signal to display gradations.

45. A method for operating a light emitting device a plurality of pixels each having a light emitting device comprising organic material, comprising steps of:

measuring the total of a current flowing between a first electrode and a second electrode of the light emitting devices provided in at least two of the plurality of pixels;

comparing the measured current value and a reference current value; and

correcting a voltage between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels for making the value of the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels close to the reference current value based on a difference between the measured current value and the reference current value,

wherein a specific image is displayed when the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels is measured, and

wherein the reference current value differs depending on an image displayed when the total of the current flowing between the first electrode and the second electrode of the light emitting devices provided in the at least two of the plurality of pixels is measured.