Liquid Crystal Display Device and Method of Driving the Same

• US 20090153460A1
• Filed: 12/12/2008
• Published: 06/18/2009
• Est. Priority Date: 12/18/2007
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Corporation of America (Panasonic Holdings Corporation)
• Original Assignee: Hitachi Displays Limited (Japan Display Incorporated)
• Inventors: TAKEDA, Nobuhiro
• Granted Patent: US 8,134,530 B2
• Time in Patent Office: Days
• US Class Current: 345/98
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 2360/18 Use of a frame buffer in a display terminal, inclusive of the display panel
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

To change a proportion of a black image display period based on an image brightness in one frame, improving a moving image performance while suppressing a reduction in luminance. A method of driving a liquid crystal display device which includes a liquid crystal display panel having plural pixels, and displays a black image after displaying a video in each pixel, includes: when taking a period for which the video is displayed as a video display period, and a period for which the black image is displayed as a black image display period, based on an image brightness in one frame, changing a ratio of the black image display period to the video display period.

Claims

1. A method of driving a liquid crystal display device which, including a liquid crystal display panel having a plurality of pixels, in each pixel, displays a black image after displaying a video, the method comprising:

when taking a period for which the video is displayed as a video display period, and a period for which the black image is displayed as a black image display period, based on a video brightness in one frame, changing a ratio of the black image display period to the video display period.

2. A liquid crystal display device comprising:

a liquid crystal display panel having a plurality of pixels, a plurality of video lines and a plurality of scan lines;

a video line drive circuit which supplies each of the video lines with a video voltage and a black image voltage;

a scan line drive circuit which supplies each of the scan lines with a video selection scan voltage for writing the video voltage and a black image selection scan voltage for writing the black image voltage; and

a display control circuit which controls the video line drive circuit and the scan line drive circuit, wherein

the scan line drive circuit, as well as supplying the scan lines, in order, with the video selection scan voltage, supplies the scan lines, in order, with the black image selection scan voltage for writing the black image voltage, and supplies the scan lines with the video selection scan voltage and the black image selection scan voltage alternately,

the video line drive circuit supplies each of the video lines with the video voltage when the scan line drive circuit is supplying the scan lines with the video selection scan voltage, and supplies each of the video lines with the black image voltage when the scan line drive circuit is supplying the scan lines with the black image selection scan voltage, and

the display control circuit has a black image insertion control circuit which, based on a video brightness obtained with the video voltage in one frame, changes a position of a scan line to be supplied next with the black image selection scan voltage after a scan line has been supplied with the video selection scan voltage, changing an insertion ratio of the black image.

3. The liquid crystal display device according to claim 2, wherein the black image insertion control circuit comprises:

a counting circuit which counts a quantity of data, among input display data in one frame, for each gradation;

a gradation conversion factor calculation circuit which, based on a result of the counting in the counting circuit, calculates an accumulated data quantity from a minimum gradation to each gradation on a gradation by gradation basis, and outputs a gradation, in which the accumulated data quantity calculated is equal to or higher than a preset data enlargement threshold, as a gradation conversion factor;

a display data conversion circuit which, based on the gradation conversion factor output from the gradation conversion factor calculation circuit, converts input display data of a gradation higher than a gradation conforming to the gradation conversion factor into output display data of a maximum gradation, and also, based on a predetermined relational expression, converts input display data from a minimum gradation to the gradation conforming to the gradation conversion factor into the output display data from the minimum gradation to the maximum gradation, and outputs them to the video line drive circuit; and

a scan control signal generation circuit which, based on the gradation conversion factor output from the gradation conversion factor calculation circuit, generates a control signal which selects a position of a scan line to be supplied next with the black image selection scan voltage after the scan line has been supplied with the video selection scan voltage, and outputs it to the scan line drive circuit.

4. The liquid crystal display device according to claim 3, wherein

when a gradation of the input display data is denoted by Kin, a gradation of the output display data by Kout, the gradation conversion factor by Kth, and the maximum gradation of the output display data by Kout-max, the display data conversion circuit converts the input display data into the output display data of gradations represented by the following equations.

Kout=(Kout-max/Kth)×

Kin (where Kin≦

Kth)

Kout=Kout-max (where Kth<

Kin)

5. The liquid crystal display device according to claim 3, wherein

the display data conversion circuit, referring to a look-up table, converts the input display data of the gradation higher than the gradation conforming to the gradation conversion factor into the output display data of the maximum gradation, and converts the input display data from the minimum gradation to the gradation conforming to the gradation conversion factor into the output display data from the minimum gradation to the maximum gradation.

6. The liquid crystal display device according to claim 3, wherein

the scan control signal generation circuit obtains a luminance of the liquid crystal display panel at a time of the gradation conforming to the gradation conversion factor from a gradation-luminance characteristic of the liquid crystal display panel in a case in which no black image insertion is carried out, obtains a black insertion ratio corresponding to the obtained luminance from a black insertion ratio-maximum luminance characteristic of the liquid crystal display panel, and generates a control signal which selects a position of a next scan line to be supplied with the black image selection scan voltage after the scan line has been supplied with the video selection scan voltage.

7. The liquid crystal display device according to claim 4, wherein

the scan control signal generation circuit obtains a luminance of the liquid crystal display panel at a time of the gradation conforming to the gradation conversion factor from a gradation-luminance characteristic of the liquid crystal display panel in a case in which no black image insertion is carried out, obtains a black insertion ratio corresponding to the obtained luminance from a black insertion ratio-maximum luminance characteristic of the liquid crystal display panel, and generates a control signal which selects a position of a next scan line to be supplied with the black image selection scan voltage after the scan line has been supplied with the video selection scan voltage.

8. The liquid crystal display device according to claim 5, wherein

the scan control signal generation circuit obtains a luminance of the liquid crystal display panel at a time of the gradation conforming to the gradation conversion factor from a gradation-luminance characteristic of the liquid crystal display panel in a case in which no black image insertion is carried out, obtains a black insertion ratio corresponding to the obtained luminance from a black insertion ratio-maximum luminance characteristic of the liquid crystal display panel, and generates a control signal which selects a position of a next scan line to be supplied with the black image selection scan voltage after the scan line has been supplied with the video selection scan voltage.