Liquid crystal display device and driving method thereof

• US 8,698,717 B2
• Filed: 12/15/2010
• Issued: 04/15/2014
• Est. Priority Date: 12/18/2009
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Arasawa, Ryo, Toyotaka, Kouhei
• Primary Examiner(s): Zhou, Hong
• Application Number:
  US12/968,334
• Publication Number:
  US 20110148846A1
• Time in Patent Office: 1,217 Days
• Field of Search: 345 87-100, 345204-211
• US Class Current: 345/87
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• 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 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2340/16 Determination of a pixel data signal depending on the signal applied in the previous frame
• CPC Class Codes: G09G 3/3614 Control of polarity reversal in general
• CPC Class Codes: G09G 3/3696 Generation of voltages supplied to electrode drivers
• CPC Class Codes: H01L 27/1225 with semiconductor materials not belonging to the group IV of the periodic table, e.g. InGaZnO

Abstract

Disclosed is a liquid crystal display device and a driving method thereof for displaying an image, in which the polarity of a voltage applied to the liquid crystal element is inverted in a first frame period and a second frame period which are sequential. The voltage applied to the liquid crystal element is compensated in the case where images of the first frame period and the second frame period are judged as a still image as a result of comparison of the image of the first frame period with the image of the second frame period and the absolute value of the voltage applied to the liquid crystal element in the first frame period is different from that of the voltage applied to the liquid crystal element in the second frame period.

Claims

1. A driving method of a liquid crystal display device comprising a liquid crystal element, the driving method comprising:

supplying data of an image signal to the liquid crystal element in a first frame period;

stopping supply of the data in second to n-th frame periods, wherein n is a natural number larger than 1;

inverting a polarity of a voltage, which is applied to the liquid crystal element, between the n-th frame period and a (n+1)-th frame period; and

compensating the voltage when an absolute value of the voltage in the n-th frame period is different from an absolute value of the voltage in the (n+1)-th frame period, so that the absolute value of the voltage in the n-th frame period is the same as the absolute value of the voltage in the (n+1)-th frame period,

wherein the liquid crystal element is electrically connected to a transistor which comprises an oxide semiconductor in a channel formation region, and

wherein a still image is formed in the first to (n+1)th frame periods.

2. The driving method according to claim 1,

wherein the liquid crystal element comprises a pixel electrode and a counter electrode with a liquid crystal provided therebetween, and

wherein the compensation of the voltage is performed by changing a potential of the counter electrode.

3. The driving method according to claim 1,

wherein a carrier concentration of the channel formation region is less than 1×

10¹⁴ /cm³.

4. The driving method according to claim 1,

wherein the oxide semiconductor comprises In, Ga, and Zn.

5. The driving method according to claim 1,

wherein the liquid crystal element is electrically connected to a capacitor, and

wherein the liquid crystal display device comprises a node which is electrically connected to the transistor, the capacitor, and the liquid crystal element and which is directly connected only to the transistor, the capacitor, and the liquid crystal element.

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

counting number of continuous frame periods which have the same data of an image signal, wherein supply of the data to the liquid crystal element is stopped during the continuous frame periods;

inverting a polarity of a voltage, which is applied to the liquid crystal element, when the number exceeds a standard value; and

compensating the voltage, so that an absolute value of the voltage is maintained after the inversion of the polarity,

wherein the liquid crystal element is electrically connected to a transistor which comprises an oxide semiconductor in a channel formation region.

7. The driving method according to claim 6,

wherein the liquid crystal element comprises a pixel electrode and a counter electrode with a liquid crystal provided therebetween, and

wherein the compensation of the voltage is performed by changing a potential of the counter electrode.

8. The driving method according to claim 6,

wherein a carrier concentration of the channel formation region is less than 1×

10¹⁴ /cm³.

9. The driving method according to claim 6,

wherein the oxide semiconductor comprises In, Ga, and Zn.

10. The driving method according to claim 6,

wherein the liquid crystal element is electrically connected to a capacitor, and

wherein the liquid crystal display device comprises a node which is electrically connected to the transistor, the capacitor, and the liquid crystal element and which is directly connected only to the transistor, the capacitor, and the liquid crystal element.

11. A liquid crystal display device comprising:

a display panel comprising;

a liquid crystal element;

a transistor electrically connected to the liquid crystal element, the transistor comprising an oxide semiconductor in a channel formation region; and

a driver circuit; and

a display control circuit configured to supply an image signal to the driver circuit in a first frame period and to stop supply of an image signal in second to n-th frame periods, wherein n is a natural number larger than 1,

wherein the driver circuit is configured to invert polarity of a voltage, which is applied to the liquid crystal element, between the n-th frame period and a (n+1)-th frame period,

wherein the driver circuit is further configured to compensate the voltage when an absolute value of the voltage in the n-th frame period is different from an absolute value of the voltage in the (n+1)-th frame period, so that the absolute value of the voltage in the n-th frame period is the same as the absolute value of the voltage in the (n+1)-th frame period,

wherein a still image is formed in the first to (n+1)th frame periods.

12. The liquid crystal display device according to claim 11, further comprising a memory circuit,

wherein the memory circuit is configured to store data of the first to n-th frame periods.

13. The liquid crystal display device according to claim 12, further comprising a comparison circuit,

wherein the comparison circuit is configured to compare data of m-th frame period with data of (m+1)-th frame period, wherein m is a natural number smaller than n, and

wherein the comparison circuit is further configured to judge whether the data of the m-th frame period is the same as the data of the (m+1)-th frame period.

14. The liquid crystal display device according to claim 13, further comprising a selection circuit,

wherein the selection circuit is configured to stop supply of the image signal of the (m+1)-th frame period to the display control circuit when the comparison circuit judges the data of the (m+1)-th frame period as being the same as the data of the m-th frame period.

15. The liquid crystal display device according to claim 11, further comprising a counting circuit,

wherein the counting circuit is configured to count number of continuous frame periods which are judged as having the same data as the data of the first image signal.

16. The liquid crystal display device according to claim 11, further comprising a compensation circuit,

wherein the compensation circuit is configured to compare the voltage applied to the liquid crystal element in the n-th frame period with that in the (n+1)-th frame period.

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

wherein a carrier concentration of the channel formation region is less than 1×

10¹⁴ /cm³.

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

wherein the oxide semiconductor comprises In, Ga, and Zn.

19. The liquid crystal display device according to claim 11, further comprising a capacitor,

wherein the liquid crystal display device comprises a node which is electrically connected to the transistor, the capacitor, and the liquid crystal element and which is directly connected only to the transistor, the capacitor, and the liquid crystal element.

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

wherein the display panel comprises a display portion comprising the liquid crystal element and the transistor,

wherein the liquid crystal display device further comprises a memory circuit outside of the display panel, and

wherein the memory circuit is configured to hold data of the image signal.