Display device and electronic device

• US 20060038804A1
• Filed: 05/06/2005
• Published: 02/23/2006
• Est. Priority Date: 05/21/2004
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Abe, Hiroko, Seo, Satoshi, Osame, Mitsuaki, Hayakawa, Masahiko, Miyagawa, Keisuke, Anzai, Aya, Koyama, Jun, Yamazaki, Shunpei, Yamazaki, Yu, Ando, Yukari
• Granted Patent: US 7,482,629 B2
• Time in Patent Office: Days
• US Class Current: 345/204
• CPC Class Codes: G09G 2300/08 Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2310/0256 with the purpose of reversing the voltage across a light emitting or modulating element within a pixel
• CPC Class Codes: G09G 2310/0275 Details of drivers for data electrodes, other than drivers for liquid crystal, plasma or OLED displays, not related to handling digital grey scale data or to communication of data to the pixels by means of a current
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• 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 2330/02 Details of power systems and of start or stop of display operation
• CPC Class Codes: G09G 2330/12 Test circuits or failure detection circuits included in a display system, as permanent part thereof
• CPC Class Codes: G09G 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: H10K 2102/3031 Two-side emission, e.g. transparent OLEDs [TOLED]
• CPC Class Codes: H10K 59/12 Active-matrix OLED [AMOLED] displays

Abstract

A display device where the influence of variations in current of the light emitting element due to changes in ambient temperature and changes with time can be suppressed. The display device of the invention has a light emitting element, a driving transistor connected in series to the light emitting element, a monitoring light emitting element, a limiter transistor connected in series to the monitoring light emitting element, a constant current source for supplying a constant current to the monitoring light emitting element, and a circuit for outputting a potential equal to an inputted potential. A first electrode of the light emitting element is connected to an output terminal of the circuit through the driving transistor, and a first electrode of the monitoring light emitting element is connected to an input terminal of the circuit through the limiter transistor. The channel length L1 and the channel width W1 of the driving transistor, and the channel length L2 and the channel width W2 of the limiter transistor satisfy L1/W1:L2/W2=1:2 to 1:10.

Claims

1. A display device comprising:

a first light emitting element;

a driving transistor connected in series to the first light emitting element;

a monitoring second light emitting element;

a limiter transistor connected in series to the monitoring second light emitting element;

a constant current source for supplying a constant current to the monitoring second light emitting element; and

a circuit for outputting a potential corresponding to a potential which is inputted to said circuit,

wherein a first electrode of the first light emitting element is connected to an output terminal of the circuit through the driving transistor;

wherein a first electrode of the monitoring second light emitting element is electrically connected to an input terminal of the circuit through the limiter transistor; and

wherein a channel length L1 and a channel width W1 of the driving transistor, and a channel length L2 and a channel width W2 of the limiter transistor satisfy L1/W1;

L2/W2=1;

2 to 1;

10.

10. The display device according to claim 1, wherein the circuit is a buffer amplifier.

11. The display device according to claim 1, wherein a second electrode of the first light emitting element and a second electrode of the monitoring second light emitting element are maintained at a constant potential.

12. The display device according to claim 1, wherein the first light emitting element and the monitoring second light emitting element are provided over the same substrate.

13. An electronic device comprising the display device according to claim 1.

2. A display device comprising:

a first light emitting element;

a monitoring second light emitting element;

a transistor connected in series to the monitoring second light emitting element;

a constant current source for supplying a constant current to the monitoring second light emitting element; and

a circuit for outputting a potential corresponding to a potential which is inputted to said circuit,

wherein a first electrode of the first light emitting element is electrically connected to an output terminal of the circuit;

wherein a first electrode of the monitoring second light emitting element, a gate electrode of the transistor, and one of a source electrode and a drain electrode of the transistor are connected to an input terminal of the circuit; and

wherein the other of the source electrode and the drain electrode of the transistor is connected to an AC power supply.

14. The display device according to claim 2, wherein the circuit is a buffer amplifier.

15. The display device according to claim 2, wherein a second electrode of the first light emitting element and a second electrode of the monitoring second light emitting element are maintained at a constant potential.

16. The display device according to claim 2, wherein the first light emitting element and the monitoring second light emitting element are provided over the same substrate.

17. An electronic device comprising the display device according to claim 2.

3. A display device comprising:

a first light emitting element;

a monitoring second light emitting element;

a constant current source for supplying a constant current to the monitoring second light emitting element;

a circuit for outputting a potential corresponding to a potential which is inputted to said circuit;

a capacitor connected to an input terminal of the circuit;

a first switch provided between a first electrode of the first light emitting element and an output terminal of the circuit;

a second switch provided between the first electrode of the first light emitting element and an AC power supply;

a third switch provided between a first electrode of the monitoring second light emitting element and the input terminal of the circuit; and

a fourth switch provided between the first electrode of the monitoring second light emitting element and the AC power supply.

4. The display device according to claim 3, comprising a control circuit for applying a forward bias voltage to the first light emitting element and the monitoring second light emitting element while bringing the first switch and the third switch into a conductive state whereas the second switch and the fourth switch into a non-conductive state.

5. The display device according to claim 3, comprising a control circuit for applying a reverse bias voltage to the first light emitting element and the monitoring second light emitting element while bringing the first switch and the third switch into a non-conductive state whereas the second switch and the fourth switch into a conductive state.

18. The display device according to claim 3, wherein the circuit is a buffer amplifier.

19. The display device according to claim 3, wherein a second electrode of the first light emitting element and a second electrode of the monitoring second light emitting element are maintained at a constant potential.

20. The display device according to claim 3, wherein the first light emitting element and the monitoring second light emitting element are provided over the same substrate.

21. An electronic device comprising the display device according to claim 3.

6. A display device comprising:

a first light emitting element;

a monitoring second light emitting element;

a transistor connected in series to the monitoring second light emitting element; and

a circuit for outputting a potential corresponding to a potential which is inputted to said circuit;

wherein a first electrode of the first light emitting element is electrically connected to an output terminal of the circuit;

wherein a first electrode of the monitoring second light emitting element and one of a source electrode and a drain electrode of the transistor are connected to an input terminal of the circuit;

wherein a gate electrode of the transistor is connected to a first power supply; and

wherein the other of the source electrode and the drain electrode of the transistor is connected to a second power supply.

7. The display device according to claim 6, wherein the transistor operates in a saturation region.

22. The display device according to claim 6, wherein the circuit is a buffer amplifier.

23. The display device according to claim 6, wherein a second electrode of the first light emitting element and a second electrode of the monitoring second light emitting element are maintained at a constant potential.

24. The display device according to claim 6, wherein the first light emitting element and the monitoring second light emitting element are provided over the same substrate.

25. An electronic device comprising the display device according to claim 6.

8. A display device comprising:

a first light emitting element;

a monitoring second light emitting element;

a constant current source for supplying a constant current to the monitoring second light emitting element;

a circuit for outputting a potential corresponding to a potential which is inputted to said circuit; and

a resistor provided between a first electrode of the monitoring second light emitting element and an input terminal of the circuit;

wherein a first electrode of the first light emitting element is electrically connected to an output terminal of the circuit.

26. The display device according to claim 8, wherein the circuit is a buffer amplifier.

27. The display device according to claim 8, wherein a second electrode of the first light emitting element and a second electrode of the monitoring second light emitting element are maintained at a constant potential.

28. The display device according to claim 8, wherein the first light emitting element and the monitoring second light emitting element are provided over the same substrate.

29. An electronic device comprising the display device according to claim 8.

9. A display device comprising:

a first light emitting element;

a switching transistor;

a monitoring second light emitting element;

a forward bias transistor connected in series to the monitoring second light emitting element;

a constant current source for supplying a constant current to the monitoring second light emitting element; and

a circuit for outputting a potential corresponding to a potential which is inputted to said circuit;

wherein a first electrode of the first light emitting element is electrically connected to an output terminal of the circuit;

wherein a first electrode of the monitoring second light emitting element is connected to an input terminal of the circuit;

wherein a gate electrode of the switching transistor and a gate electrode of the forward bias transistor are connected to a gate line; and

wherein one of a source electrode and a drain electrode of the forward bias transistor is connected to the input terminal of the circuit and the other of a source electrode and a drain electrode of the forward bias transistor is connected to a forward bias power supply.

30. The display device according to claim 9, wherein the circuit is a buffer amplifier.

31. The display device according to claim 9, wherein a second electrode of the first light emitting element and a second electrode of the monitoring second light emitting element are maintained at a constant potential.

32. The display device according to claim 9, wherein the first light emitting element and the monitoring second light emitting element are provided over the same substrate.

33. An electronic device comprising the display device according to claim 9.