Liquid crystal display device and driving method therefor

Patent metadata

Field	Value
Publication number	US-9865202-B2
Application number	US-201414779682-A
Country	US
Kind code	B2
Filing date	Feb 24, 2014
Priority date	Apr 2, 2013
Publication date	Jan 9, 2018
Grant date	Jan 9, 2018

Abstract

The invention provides a liquid crystal display device capable of preventing a reduction in display quality by suppressing the occurrence of flicker during alternating-voltage drive, as well as a method for driving the same.
Overshoot drive is performed during a first frame period, which is shortened to such an extent that a “positive effective area” and a “negative effective area” are approximately equal in size. The duration of the first frame period is set to be greater than or equal to a quarter of one frame period at a refresh rate of 60 Hz but less than one frame period. This renders it possible to make adjustments such that luminance is inhibited from abruptly dropping immediately after a polarity change, and also luminance is prevented from becoming excessively high due to overshoot drive, and therefore, the occurrence of flicker due to flexoelectric polarization during alternating-voltage drive can be suppressed.

First claim

The invention claimed is:

1. A liquid crystal display device performing alternating-voltage drive, comprising:
a plurality of scanning signal lines formed on an insulating substrate;
a plurality of data signal lines crossing each of the scanning signal lines;
a plurality of pixel forming portions formed at respective intersections of the scanning signal lines and the data signal lines;
a grayscale control portion configured to output either a correction image signal or an image signal, the correction image signal being obtained by subjecting input image data to a grayscale correction process for correcting a temporal signal change, the image signal being the input image data that is not subjected to the grayscale correction process;
a scanning signal line driver circuit configured to sequentially select and scan the scanning signal lines;
a data signal line driver circuit configured to apply either a data voltage or a grayscale correction voltage to the data signal lines, the data voltage being generated in accordance with the image signal and corresponding to a target grayscale value, the grayscale correction voltage being generated by correcting the data voltage in accordance with the correction image signal; and
a display control portion configured to control the scanning signal line driver circuit and the data signal line driver circuit, wherein,
the display control portion writes the grayscale correction voltage to the pixel forming portions during a first frame period, as well as the data voltage having the same polarity as the grayscale correction voltage during a second frame period, thereby performing control such that screen refresh is performed,
the first frame period has a duration greater than or equal to a quarter of a frame period at a refresh rate of 60 Hz but less than the frame period,
the grayscale control portion includes:
a frame memory having stored the input image data for each frame;
a table having, correction values stored corresponding to previous-frame grayscale values and current-frame grayscale values for the input image data;
a comparator circuit configured to obtain a current-frame grayscale value for the input image data and a previous-frame grayscale value for the input image data stored in the frame memory, and output the obtained values to the table; and
an adder circuit configured to output either the correction image signal or the image signal to the data signal line driver circuit in accordance with the input image data,

the table has the correction values stored corresponding to combinations of the current-frame grayscale values and the previous-frame grayscale values for the input image data, and outputs a corresponding correction value from among the combinations to the adder circuit when the comparator circuit provides the table with a current-frame grayscale value and a previous-frame grayscale value for the input image data, and
the adder circuit outputs the correction image signal after correcting the grayscale for the input image data with the correction value provided by the table, or outputs the image signal without correcting the grayscale value for the input image data.

2. The liquid crystal display device according to claim 1 , wherein the second frame period has the same duration as the first frame period.

3. The liquid crystal display device according to claim 1 , wherein the display control portion sets a pause period upon completion of the writing of the data voltage to the pixel forming portions during the second frame period, whereby the writing of the data voltage to the pixel forming portions is paused.

4. The liquid crystal display device according to claim 1 , wherein the display control portion includes a drive frequency control circuit configured to, upon acquisition of update information from the comparator circuit indicating that the input image data has not yet been updated, adjust the duration of the first frame period to be less than the duration of the frame period on the basis of the update information.

5. The liquid crystal display device according to claim 4 , wherein,
the update information includes first update information and second update information, the first update information indicating that the input image data has not yet been updated, the second update information indicating that the input image data has been updated, and
the display control portion further includes a drive/pause control circuit configured to generate a drive/pause control signal to switch between a drive period and a pause period when the first update information is provided by the comparator circuit or only set a data voltage writing period in which the data voltage is written when the second update information is provided, the drive period consisting of a grayscale correction period in which the grayscale correction voltage is written and the data voltage writing period.

6. The liquid crystal display device according to claim 1 , further comprising a temperature sensor configured to measure an ambient temperature around the liquid crystal display device, wherein,
the table includes a plurality of subtables having stored different correction values for predetermined temperature ranges, and
the table selects from among the subtables one that corresponds to temperature information provided by the temperature sensor in accordance with the temperature information.

7. The liquid crystal display device according to claim 1 , wherein the pixel forming portion includes a thin-film transistor being connected at a control terminal to the scanning signal line, at a first conductive terminal to the data signal line, and at a second conductive terminal to a pixel electrode to which the data voltage or the grayscale correction voltage is to be applied, the thin-film transistor having a channel layer formed with an oxide semiconductor.

8. The liquid crystal display device according to claim 7 , wherein the oxide semiconductor includes indium, gallium, zinc, and oxygen.

9. The liquid crystal display device according to claim 3 , wherein the data signal line driver circuit applies a ground potential to the data signal line during the pause period.

10. The liquid crystal display device according to claim 3 , wherein the data signal line driver circuit sets the data signal line at a floating potential during the pause period.

11. The liquid crystal display device according to claim 1 , wherein the insulating substrate has a common electrode and a pixel electrode formed thereon such that one electrode is superimposed over the other electrode with an insulating film positioned therebetween, the overlying electrode having a plurality of openings provided therein.

12. The liquid crystal display device according to claim 1 , wherein alternating-voltage drive is performed in a dot-by-dot inversion drive mode, a line-by-line inversion drive mode, a column-by-column inversion drive mode, or a frame-by-frame inversion drive mode.

13. An alternating-voltage driving method for a liquid crystal display device configured to alternately repeat a refresh period for updating an image with an input image data and a pause period for pausing updating of the image, comprising:
a grayscale correction voltage application step for applying a grayscale correction voltage to a liquid crystal layer by writing the grayscale correction voltage to a pixel forming portion in case where a polarity of a data voltage is switched by being provided with updated image information indicating that the input image data is not updated during a time period having a duration greater than or equal to a quarter of a frame period at a refresh rate of 60 Hz;

Assignees

• Sharp Kk

Inventors

• Kobayashi Fumiyuki
• Yamato Asahi
• Inada Ken

Classifications

• G09G2320/0247

  Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes · CPC title

• G09G2340/0435

  Change or adaptation of the frame rate of the video stream · CPC title

• G09G3/3607 Primary

  for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels (display of colours in flat matrix panels other than liquid crystal displays G09G3/2003; grey scales specific for television H04N3/127) · CPC title

• G02F1/133707

  Structures for producing distorted electric fields, e.g. bumps, protrusions, recesses, slits in pixel electrodes · CPC title

• G02F2203/30

  Gray scale · CPC title