Light emitting device

• US 6,788,003 B2
• Filed: 01/29/2002
• Issued: 09/07/2004
• 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: Iwabuchi, Tomoyuki, Inukai, Kazutaka
• Primary Examiner(s): Lee, Wilson
• Assistant Examiner(s): A, Mind Dien
• Application Number:
  US10/060,709
• Publication Number:
  US 20020125831A1
• Time in Patent Office: 952 Days
• Field of Search: 315/169.1, 315/169.3, 315/169.4, 345/76, 345/82, 345/84, 345/88, 345/90, 345/93, 345/23
• US Class Current: 315/169.3
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• 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 2300/0866 by means of changes in the pixel supply voltage
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• 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 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• 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 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3266 Details of drivers for scan electrodes
• CPC Class Codes: G09G 3/3275 Details of drivers for data electrodes
• 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: 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

A light emitting device 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. Separately from a pixel portion for displaying an image, a pixel portion for measuring a driving current of the OLED is provided in the light emitting device. The driving current is measured in the pixel portion for measuring the driving current of the OLED, and a value of the voltage supplied to the above two pixel portions from a variable power supply is corrected such that the measured driving current has a reference value. 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 first pixel portion having a first OLED;

a second pixel portion having a second OLED;

first means for measuring a current flowing in the second OLED;

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

third means for correcting a voltage applied to the second OLED for making the value of the current flowing in the second OLED close to the reference current value based on a difference between the measured current value and the reference current value,

wherein the first pixel portion is input with a display video signal,

wherein the second pixel portion is input with a monitor video signal which is distinct from the display video signal, and

wherein a voltage applied to the first OLED is kept at the same level as the voltage applied to the second OLED.

7. A light emitting device according to any one of claims 1 to 6, wherein the first, second or third means are provided for each of corresponding colors of the first and second OLEDs.

24. A light emitting device according to any one of claims 1 to 6, 8, 9, 11, 15 to 17, 22 and 23 wherein a period during which the first OLED and the second OLED emit light is controlled with a digital video signal to display gradations.

25. A light emitting device according to any one of claims 1 to 6, 8, 9, 11, 15 to 17, 22 and 23 wherein the light emitting device is incorporated into an electronic device selected from the group consisting of a video camera, a digital camera, a goggles-type display, a navigation system, a sound reproduction device, note-size personal computer, a game machine, a portable information terminal, and an image reproduction apparatus including a recording medium.

2. A light emitting device comprising:

a first pixel portion provided with a plurality of first pixels each having a first OLED;

a second pixel portion provided with a plurality of second pixels each having a second OLED;

first means for measuring the total of a current flowing in all the second OLEDs;

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

third means for correcting a voltage applied to all the second OLEDs for making the value of the total of the current flowing to all the second OLEDs close to the reference current value based on a difference between the measured current value and the reference current value,

wherein the first pixel portion is input with a display video signal.

wherein the second pixel portion is input with a monitor video signal which is distinct from the display video signal, and

wherein a voltage applied to the first OLED is kept at the same level as the voltage applied to the second OLED.

3. A light emitting device comprising:

a first pixel portion provided with a plurality of first pixels each having a first OLED;

a second pixel portion provided with a plurality of second pixels each having a second OLED;

first means for measuring the total of a current flowing in all the second OLEDs;

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

third means for correcting a voltage applied to all the second OLEDs for making the value of the total of the current flowing in all the second OLEDs close to the reference current value based on a difference between the measured current value and the reference current value,

wherein the first pixel portion is input with a display video signal,

wherein the second pixel portion is input with a monitor video signal which is distinct from the display video signal,

wherein a voltage applied to the first OLED is kept at the same level as the voltage applied to the second OLED, and

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.

4. A light emitting device comprising:

a first pixel portion provided with a plurality of first pixels each having a first OLED;

a second pixel portion provided with a plurality of second pixels each having a second OLED;

first means for measuring the total of a current flowing in all the second OLEDs;

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

third means for correcting a voltage applied to all the second OLEDs for making the value of the total of the current flowing in all the second OLEDs close to the reference current value based on a difference between the measured current value and the reference current value,

wherein the first pixel portion is input with a display video signal,

wherein the second pixel portion is input with a monitor video signal which is distinct from the display video signal,

wherein a voltage applied to the first OLED is kept at the same level as the voltage applied to the second OLED, and

wherein a specific image is displayed on the second pixel portion when the total of the current flowing in all the second OLEDs is measured.

5. A light emitting device comprising:

a first pixel portion provided with a plurality of first pixels each having a first OLED;

a second pixel portion provided with a plurality of second pixels each having a second OLED;

first means for measuring the total of a current flowing in all the second OLEDs;

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

third means for correcting a voltage applied to all the second OLEDs for making the value of the total of the current flowing in all the second OLEDs close to the reference current value based on a difference between the measured current value and the reference current value,

wherein the first pixel portion is input with a display video signa,.

wherein the second pixel portion is input with a monitor video signal which is distinct from the display video signal,

wherein a voltage applied to the first OLED is kept at the same level as the voltage applied to the second OLED, and

wherein the reference current value differs depending on an image displayed on the second pixel portion when the total of the current flowing in all the second OLEDs is measured.

6. A light emitting device comprising:

a first pixel portion provided with a plurality of first pixels each having a first OLED and at least one first TFT, the first TFT controlling light emission of the first OLED;

a second pixel portion provided with a plurality of second pixels each having a second OLED and at least one second TFT, the second TFT controlling light emission of the second OLED;

first means for measuring the total of a current flowing in all the second OLEDs;

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

third means for correcting a voltage applied to all the second OLEDs for making the value of the total of the current flowing in all the second OLEDs close to the reference current value based on a difference between the measured current value and the reference current value,

wherein the first pixel portion is input with a display video signal,

wherein the second pixel portion is input with a monitor video signal which is distinct from the display video signal, and

wherein a voltage applied to the first OLED is kept at the same level as the voltage applied to the second OLED.

8. A light emitting device comprising:

a display pixel portion having a first OLED;

a monitor pixel portion having a second OLED;

a variable power supply;

an ammeter for measuring a current flowing in the second OLED; and

a correction circuit for comparing the measured current value and a reference current value and correcting a voltage applied to the second OLED for making the value of the current flowing in the second OLED close to the reference current value by controlling the variable power supply,

wherein the display pixel portion is input with a display video signal,

wherein the monitor pixel portion is input with a monitor video signal which is distinct from the display video signal, and

wherein a voltage applied to the first OLED is kept at the same level as the voltage applied to the second OLED.

10. A light emitting device according to claim 8 or claim 9, wherein the variable power supply, the ammeter and the correction circuit are provided for each of corresponding colors of the first and second OLEDs.

9. A light emitting device comprising:

a display pixel portion having a plurality of first OLEDs;

a monitor pixel portion having a plurality of second OLEDs;

an ammeter for measuring the total of a current flowing in all the plurality of second OLEDs; and

a correction circuit for comparing the measured current value and a reference current value and correcting a voltage applied to all the plurality of second OLEDs for making the value of the total of the current flowing in all the plurality of second OLEDs close to the reference current value by controlling a variable power supply,

wherein the display pixel portion is input with a display video signal,

wherein the monitor pixel portion is input with a monitor video signal which is distinct from the display video signal, and

wherein a voltage applied to the plurality of first OLEDs is kept at the same level as the voltage applied to the plurality of second OLEDs.

11. A light emitting device comprising:

a first OLED;

a second OLED;

a first variable power supply;

a second variable power supply;

an ammeter for measuring a current flowing in the second OLED; and

a correction circuit for comparing the measured current value and a reference current value and correcting a voltage applied to the second OLED for making the value of the current flowing in the second OLED close to the reference current value by controlling the second variable power supply,

wherein a voltage applied to the first OLED is kept at the same level as the voltage applied to the second OLED by the first variable power supply.

12. A light emitting device according to any one of claims 8, 9 and 11, wherein a second substrate on which the correction circuit and the ammeter are formed is attached onto a first substrate on which the first and second OLEDs are formed.

13. A light emitting device according to any one of claims 8, 9 and 11, wherein a second substrate on which the correction circuit and the ammeter are formed is attached onto a first substrate on which the first and second OLEDs are formed by a COG method.

14. A light emitting device according to any one of claims 8, 9 and 11, wherein a second substrate on which the correction circuit and the ammeter are formed is attached onto a first substrate on which the first and second OLEDs are formed by a wire bonding method.

19. A light emitting device according to any one of claims 8, 9, 11 and 15 to 17, wherein a second substrate on which the correction circuit and the ammeter are formed is attached onto a first substrate on which the plurality of first OLEDs and the plurality of second OLEDs are formed.

20. A light emitting device according to any one of claims 8, 9, 11 and 15 to 17, wherein a second substrate on which the correction circuit and the ammeter are formed is attached onto a first substrate on which the plurality of first OLEDs and the plurality of second OLEDs are formed by a COG method.

21. A light emitting device according to any one of claims 8, 9, 11 and 15 to 17, wherein a second substrate on which the correction circuit and the ammeter are formed is attached onto a first substrate on which the plurality of first OLEDs and the plurality of second OLEDs are formed by a wire bonding method.

15. A light emitting device comprising:

a plurality of first OLEDs;

a plurality of second OLEDs;

an ammeter for measuring the total of a current flowing in all the plurality of second OLEDs; and

a correction circuit for comparing the measured current value and a reference current value and correcting a voltage applied to all the plurality of second OLEDs for making the value of the total of the current flowing in all the plurality of second OLEDs close to the reference current value by controlling a variable power supply,

wherein a voltage applied to the plurality of first OLEDs is kept at the same level as the voltage applied to the plurality of second OLEDs, and

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.

18. A light emitting device according to any one of claims 15 to 17, wherein the variable power supply, the ammeter, and the correction circuit are provided for each of corresponding colors of the plurality of first OLEDs and the plurality of second OLEDs.

16. A light emitting device comprising:

a first pixel portion having a plurality of first OLEDs;

a second pixel portion having a plurality of second OLEDs;

an ammeter for measuring the total of a current flowing in all the plurality of second OLEDs; and

a correction circuit for comparing the measured current value and a reference current value and correcting a voltage applied to all the plurality of second OLEDs for making the value of the total of the current flowing in all the plurality of second OLEDs close to the reference current value by controlling a variable power supply,

wherein a voltage applied to the plurality of first OLEDs is kept at the same level as the voltage applied to the plurality of second OLEDs, and

wherein a specific image is displayed on the second pixel portion when the total of the current flowing in all the plurality of second OLEDs is measured.

17. A light emitting device comprising:

a first pixel portion having a plurality of first OLEDs;

a second pixel portion having a plurality of second OLEDs;

an ammeter for measuring the total of a current flowing in all the plurality of second OLEDs; and

a correction circuit for comparing the measured current value and a reference current value and correcting a voltage applied to all the plurality of second OLEDs for making the value of the total of the current flowing in all the plurality of second OLEDs close to the reference current value by controlling a variable power supply,

wherein a voltage applied to the plurality of first OLEDs is kept at the same level as the voltage applied to the plurality of second OLEDs, and

wherein the reference current value differs depending on an image displayed on the second pixel portion when the total of the current flowing in all the plurality of second OLEDs is measured.

22. A light emitting device comprising:

a first pixel portion having a first OLED;

a second pixel portion having a second OLED;

first means for measuring a current flowing in the second OLED;

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

third means for correcting a voltage applied to the first and second OLEDs based on a difference between the measured current value and the reference current value,

wherein the first pixel portion is input with a display video signal, and

wherein the second pixel portion is input with a monitor video signal which is distinct from the display video signal.

23. A light emitting device comprising:

a first OLED;

a second OLED;

a variable power supply;

an ammeter for measuring a current flowing in the second OLED; and

a correction circuit for comparing the measured current value and a reference current value and correcting a voltage applied to the first and second OLEDs.