LIQUID CRYSTAL DISPLAY DEVICE AND DRIVING METHOD OF THE SAME

• US 20120032942A1
• Filed: 07/29/2011
• Published: 02/09/2012
• Est. Priority Date: 08/06/2010
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Toyotaka, Kouhei, Miyake, Hiroyuki, Arasawa, Ryo, Kusunoki, Koji, Murakawa, Tsutomu
• Granted Patent: US 8,692,823 B2
• Time in Patent Office: Days
• US Class Current: 345/212
• CPC Class Codes: G09G 2320/103 Detection of image changes, e.g. determination of an index representative of the image change
• CPC Class Codes: G09G 2330/04 Display protection
• CPC Class Codes: G09G 3/20 for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
• CPC Class Codes: G09G 3/36 using liquid crystals
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3688 suitable for active matrices only

Abstract

Provided is a liquid crystal display device having a pixel including a transistor and a liquid crystal element and a protection circuit electrically connected to one of a source and a drain of the transistor through a data line. The protection circuit includes a first terminal supplied with a first power supply potential and a second terminal supplied with a second power supply potential higher than the first power supply potential. In a moving image display mode, an image signal is input from the data line to the liquid crystal element through the transistor, and the first power supply potential is set at the first potential. In a still image display mode, supply of the image signal is stopped, and the first power supply potential is set at the second potential. The second potential is substantially the same as the minimum value of the image signal.

Claims

1. A liquid crystal display device comprising:

a data line configured to be supplied with an image signal;

a pixel comprising a liquid crystal element and a transistor which is electrically connected to the liquid crystal element and the data line;

a gate line capable of switching the transistor between an on state and an off state; and

a protection circuit electrically connected to the data line,

wherein the protection circuit is configured to supply a first potential to the data line when the transistor is in the on state and to supply a second potential to the data line when the transistor is in the off state, and

wherein the first potential is lower than a minimum potential of the image signal and the second potential is substantially the same as the minimum potential of the image signal.

2. The liquid crystal display device according to claim 1,

wherein the transistor comprises an oxide semiconductor layer.

3. The liquid crystal display device according to claim 1,

wherein the protection circuit comprises a first terminal and a second terminal, and

wherein the first potential and the second potential are supplied to the first terminal.

4. The liquid crystal display device according to claim 1,

wherein the protection circuit comprises a first terminal and a second terminal, and

wherein the second terminal is supplied with a third potential higher than the second potential.

5. The liquid crystal display device according to claim 4,

wherein the liquid crystal element comprises a pixel electrode and a common electrode to which a common potential is supplied, and

wherein the third potential is higher than the common potential.

6. A driving method of a liquid crystal display device comprising:

judging whether the liquid crystal display device displays a moving image or a still image;

switching a transistor in a pixel of the liquid crystal display device to an off state if the liquid crystal display device is judged to display the still image, wherein the transistor is configured to control supply of an image signal from a data line to a liquid crystal element in the liquid crystal display device; and

supplying a first potential to the data line while maintaining the off state of the transistor,

wherein the first potential is substantially the same as a minimum potential of the image signal.

7. The driving method according to claim 6,

wherein the transistor comprises an oxide semiconductor layer.

8. The driving method according to claim 6,

wherein the first potential is supplied from a protection circuit connected to the data line.

9. The driving method according to claim 8,

wherein the protection circuit is capable of supplying a second potential to the data line if the liquid crystal display device is judged to display the moving image, and

wherein the second potential is lower than the first potential.

10. A liquid crystal display device comprising a plurality of pixels each of which comprises a liquid crystal element, the liquid crystal display device comprising:

means for judging whether the liquid crystal display device displays a moving image or a still image;

means for stopping supplying an image signal from a data line to the liquid crystal element when the liquid crystal display device is judged to display the still image; and

means for holding the image signal in the liquid crystal element when the liquid crystal display device is judged to display the still image,

wherein the means for holding the image signal is capable of supplying a potential to the data line when the liquid crystal display device is judged to display the still image, and

wherein the potential is substantially the same as a minimum potential of the image signal.

11. The liquid crystal display device according to claim 10,

wherein the means for stopping supplying the image signal comprises a transistor located in each of the plurality of pixels and connected to the liquid crystal element.

12. The liquid crystal display device according to claim 11,

wherein the transistor comprises an oxide semiconductor layer.