IP Library › Granted Patent US 8,730,220

Granted Patent B2

US 8,730,220 · App. 12/047,518 · Granted May 20, 2014

Display device

Inventors: Hiroyuki Miyake (Kanagawa, JP); Atsushi Umezaki (Kanagawa, JP)

Assignee: Semiconductor Energy Laboratory Co., Ltd.

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Quick Facts

Patent No.: US 8,730,220
App. No.: 12/047,518
Granted: May 20, 2014
Kind: B2

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Abstract

To provide a display device in which reliability of a driver circuit can be improved by suppressing shift of the threshold voltage of a TFT. The minimum power supply voltage that is optimal for driving a transistor used in the driver circuit is found by actually changing voltage applied to a gate of the transistor. Specifically, voltage that is output from an output circuit included in the driver circuit when a value of power supply voltage applied to a shift register is changed is monitored. Then, a value of the power supply voltage is found such that a value of the voltage output from the output circuit satisfies a value enough to operate a pixel portion, and the driver circuit is operated using the power supply voltage.

Claims (74)

1. A display device comprising:

a pixel portion;

a scan line driver circuit including an output circuit including a transistor; and

a voltage generation circuit including a decision circuit and a voltage setting circuit,

wherein the output circuit outputs a second voltage to the pixel portion and the decision circuit when the voltage setting circuit outputs a first voltage to a gate of the transistor,

wherein the decision circuit controls the voltage setting circuit by comparing a value of the second voltage with a value of the first voltage so that the value of the first voltage is set to a certain value, and

wherein the transistor is turned on by the certain value.

2. The display device according to claim 1 , wherein the transistor is a thin film transistor.

3. The display device according to claim 1 , wherein the transistor is a thin film transistor in which an insulating film with a higher dielectric constant than that of silicon oxide is used for a gate insulating film.

4. The display device according to claim 1 , wherein the certain value is substantially the same as a minimum value in order to turn on the transistor.

5. A display device comprising:

a pixel portion;

an output circuit including first and second transistors;

a decision circuit; and

a voltage setting circuit,

wherein the output circuit outputs a second voltage to the pixel portion and the decision circuit when the voltage setting circuit outputs a first voltage to a gate of the first transistor,

wherein a clock signal is sampled by the second transistor, and is supplied to the pixel portion,

wherein the first transistor is turned on by the certain value.

6. The display device according to claim 5 , wherein the first transistor is a thin film transistor.

7. The display device according to claim 5 , wherein the first transistor is a thin film transistor in which an insulating film with a higher dielectric constant than that of silicon oxide is used for a gate insulating film.

8. The display device according to claim 5 , wherein the certain value is substantially the same as a minimum value in order to turn on the first transistor.

9. A display device comprising:

a pixel portion including a plurality of pixels;

an output circuit including first and second transistors;

a decision circuit; and

a voltage setting circuit,

wherein the output circuit outputs a second voltage to the pixel portion and the decision circuit when the voltage setting circuit outputs a first voltage to a gate of the first transistor,

wherein the plurality of pixels are selected per line by sampling a clock signal by the second transistor, and by supplying the clock signal to the pixel portion,

wherein the first transistor is turned on by the certain value.

10. The display device according to claim 9 , wherein the first transistor is a thin film transistor.

11. The display device according to claim 9 , wherein the first transistor is a thin film transistor in which an insulating film with a higher dielectric constant than that of silicon oxide is used for a gate insulating film.

12. The display device according to claim 9 , wherein the certain value is substantially the same as a minimum value in order to turn on the first transistor.

13. A display device comprising:

a pixel portion;

an output circuit including first and second transistors;

a decision circuit;

a voltage setting circuit; and

an adder included in the voltage setting circuit,

wherein the output circuit outputs a second voltage to the pixel portion and the decision circuit when the voltage setting circuit outputs a first voltage to a gate of the first transistor,

wherein a clock signal is sampled by the second transistor, and is supplied to the pixel portion,

wherein the first transistor is turned on by the certain value, and

wherein the adder applies a sum of the certain value of the first voltage and a value of a third voltage to the gate of the first transistor.

14. The display device according to claim 13 , wherein the first transistor is a thin film transistor.

15. The display device according to claim 13 , wherein the first transistor is a thin film transistor in which an insulating film with a higher dielectric constant than that of silicon oxide is used for a gate insulating film.

16. The display device according to claim 13 , wherein the certain value is substantially the same as a minimum value in order to turn on the first transistor.

17. A display device comprising:

a pixel portion;

an output circuit including first and second transistors;

a decision circuit;

a voltage setting circuit; and

an adder included in the voltage setting circuit,

wherein the output circuit outputs a second voltage to the pixel portion and the decision circuit when the voltage setting circuit outputs a first voltage to a gate of the first transistor,

wherein the plurality of pixels are selected per line by sampling a clock signal by the second transistor, and by supplying the clock signal to the pixel portion,

wherein the first transistor is turned on by the certain value, and

wherein the adder applies a sum of the certain value of the first voltage and a value of a third voltage to the gate of the first transistor.

18. The display device according to claim 17 , wherein the first transistor is a thin film transistor.

19. The display device according to claim 17 , wherein the first transistor is a thin film transistor in which an insulating film with a higher dielectric constant than that of silicon oxide is used for a gate insulating film.

20. The display device according to claim 17 , wherein the certain value is substantially the same as a minimum value in order to turn on the first transistor.

21. The display device according to claim 1 ,