LIQUID CRYSTAL DISPLAY DEVICE AND METHOD FOR DRIVING SAME

• US 20160196781A1
• Filed: 12/20/2013
• Published: 07/07/2016
• Est. Priority Date: 12/28/2012
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: TANAKA, Noriyuki, SUYAMA, Tatsuhiko, SONE, Takuya, OHMURA, Norio, UEMURA, Kentaroh, KUMADA, Kouji
• Granted Patent: US 9,607,541 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G09G 2310/0205 Simultaneous scanning of several lines in flat panels
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• CPC Class Codes: G09G 2310/08 Details of timing specific for flat panels, other than clock recovery
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 2320/0252 Improving the response speed
• CPC Class Codes: G09G 2320/0285 using tables for spatial correction of display data
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2330/022 in absence of operation, e.g. no data being entered during a predetermined time
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/2096 Details of the interface to the display terminal specific for a flat panel suitable for both CRT and flat panel G09G5/006; specific for a CRT G09G1/167
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers
• CPC Class Codes: G09G 3/3614 Control of polarity reversal in general
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3677 suitable for active matrices only
• CPC Class Codes: G09G 3/3688 suitable for active matrices only
• CPC Class Codes: G09G 5/395 Arrangements specially adapted for transferring the contents of the bit-mapped memory to the screen G09G5/399 takes precedence
• CPC Class Codes: H04N 5/63 Generation or supply of power specially adapted for television receivers

Abstract

Provided is a liquid crystal display device capable of reliably reducing power consumption during pause drive by controlling the timing of performing refresh.

When there is an image change in externally inputted RGB data, or when the number of consecutive pause frames reaches a predetermined value, if the number of immediately preceding pause frames is less than a threshold BCTH, image signal refresh is performed once, or if the number of pause frames is greater than or equal to the threshold BCTH, boost charge refresh is performed first, and then, the image signal refresh is performed. As a result, it is rendered possible to reduce flicker due to luminance reduction, and it is also rendered possible to eliminate the need to perform refresh consecutively even if the frequency of RGB data is high (e.g., 30 Hz) during pause drive.

Claims

1. A liquid crystal display device performing pause drive with a pause frame for pausing screen refresh being set between two refresh frames in which screen refresh is performed, the device comprising:

a display portion including a plurality of scanning signal lines formed on an insulating substrate, a plurality of data signal lines crossing each of the scanning signal lines, and a plurality of pixel forming portions arranged in a matrix corresponding to respective intersections of the scanning signal lines and the data signal lines;

a scanning signal line driver circuit configured sequentially to select the scanning signal lines;

a data signal line driver circuit configured to write image signal voltages to the data signal lines, the image signal voltages being generated on the basis of externally inputted image data; and

a display control circuit configured to control the operation of the scanning signal line driver circuit and the data signal line driver circuit, wherein,

the display control circuit includes;

a correction circuit configured either to output correction image data obtained by subjecting image data for a current frame to a tone emphasizing process for emphasizing a temporal change or to output the image data for the current frame without performing the tone emphasizing process; and

a first register configured to store a preset threshold,

the display control circuit determines whether the number of pause frames preceding the current frame is greater than the threshold, and

when the number of pause frames is determined to be greater than the threshold, the data signal line driver circuit applies a boost charge voltage and an image signal voltage successively to the data signal lines, the boost charge voltage being different in polarity from image data for the pause frame and being based on the correction image data outputted by the correction circuit, the image signal voltage having the same polarity as the correction image data and being based on the image data for the current frame, whereas when the number of pause frames is determined to be less than the threshold, the data signal line driver circuit applies the image signal voltage to the data signal lines, the image signal voltage being different in polarity from the image data for the pause frame.

2. The liquid crystal display device according to claim 1, wherein the display control circuit further includes an image change detection circuit configured to detect a state change of the image data for the current frame.

3. The liquid crystal display device according to claim 2, wherein,

the externally inputted image data is data that is inputted successively on a frame-by-frame basis,

the image change detection circuit detects a change in an image represented by the image data on a frame-by-frame basis, and

when there is any change detected in the image, the display control circuit starts providing both the correction image data and the image data or only the image data to the data signal line driver circuit from the next frame after the frame with the detected image change.

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

the display control circuit further includes:

a counter configured to count the number of consecutive pause frames preceding the frame determined to have a change in the image data; and

a second register configured to store a preset specific value, and

the display control circuit determines whether the number of counted pause frames is greater than the specific value regardless of the presence or absence of a change in the image, and provides both the correction image data outputted by the correction circuit and the image data successively to the data signal line driver circuit when the number is determined to be greater than the specific value, or provides only the image data to the data signal line driver circuit when the number is determined to be less than the specific value.

5. The liquid crystal display device according to claim 1, wherein,

the externally inputted image data is data that is inputted intermittently or in response to a transmission request made by the liquid crystal display device, and

upon reception of the externally inputted image data, the display control circuit starts providing both the correction image data and the image data or only the image data to the data signal line driver circuit from a frame in which the image data has been detected.

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

the display control circuit further includes:

a counter configured to count the number of consecutive pause frames preceding the frame in which the image data was detected as having been inputted; and

a second register configured to store a preset specific value, and

the display control circuit determines whether the number of counted pause frames is greater than the specific value regardless of whether the image data has been detected, and provides both the correction image data outputted by the correction circuit and the image data successively to the data signal line driver circuit when the number is determined to be greater than the specific value, or provides only the image data outputted by the correction circuit to the data signal line driver circuit when the number is determined to be less than the specific value.

7. The liquid crystal display device according to claim 2, wherein,

the display control circuit further includes first frame memory configured to hold at least the image data whose state change has been detected, the first frame memory being rewritable memory, and

when the display portion displays the refresh frame, the display control circuit reads the image data being held in the first frame memory, and provides the image data to the data signal line driver circuit.

8. The liquid crystal display device according to claim 1, wherein,

the display control circuit further includes an interface portion configured to obtain the image data and a timing signal from externally inputted data, the timing signal being required for activating the display control circuit, and

in accordance with a control signal generated from the timing signal, the display control circuit controls the timing of providing the image data or the correction image data to the data signal line driver circuit.

9. The liquid crystal display device according to claim 1, wherein the display control circuit further includes a command register configured to output the image data as RAM write data in accordance with an externally inputted command, and internally generates a timing control signal for operation control.

10. The liquid crystal display device according to claim 2, wherein the image change detection circuit detects the presence or absence of an image change by comparing a value obtained by an arithmetic operation using image data for a preceding frame and a value obtained by an arithmetic operation using image data for a current frame.

11. The liquid crystal display device according to claim 2, wherein the image change detection circuit detects the presence or absence of an image change by comparing image data for a preceding frame and image data for a current frame.

12. The liquid crystal display device according to claim 2, wherein the image change detection circuit detects the presence or absence of an image change on the basis of a predetermined signal that is externally inputted.

13. The liquid crystal display device according to claim 2, wherein the image change detection circuit includes a third register in which a value that specifies the presence or absence of an image change is externally written, and detects the presence or absence of an image change on the basis of the value written in the third register.

14. The liquid crystal display device according to claim 2, wherein the image change detection circuit is a checksum circuit configured to obtain and to compare a checksum value for the image data for the preceding frame and a checksum value for the image data for the current frame.

15. The liquid crystal display device according to claim 2, wherein the image change detection circuit detects the presence or absence of an image change on the basis of an image determination packet contained in a header of the image data for the current frame.

16. The liquid crystal display device according to claim 2, wherein,

the display control circuit further includes a command register having prestored information indicating whether the image data to be transmitted includes a changed image, and

upon each reception of the image data, the image change detection circuit senses whether the image data includes a changed image on the basis of the information stored in the command register.

17. The liquid crystal display device according to claim 1, wherein,

the correction circuit includes:

second frame memory configured to hold image data for a preceding frame, and

a lookup table configured to store a correction value for emphasizing a temporal change for each combination of a grayscale value corresponding to the image data for the preceding frame and a grayscale value corresponding to the image data for the current frame, and

when the image data for the current frame is provided, the correction circuit retrieves from the lookup table a correction value based on a grayscale value for the image data for the preceding frame and a grayscale value for the image data for the current frame, and performs the tone emphasizing process based on the retrieved correction value.

18. The liquid crystal display device according to claim 17, wherein the lookup table has correction values stored only for combinations of equal grayscale values corresponding to the image data for the preceding frame and the current frame.

19. The liquid crystal display device according to claim 1, wherein,

the pixel forming portion includes a thin-film transistor functioning as a switching element and a pixel capacitor connected to the thin-film transistor and charged with the image signal voltage, and

the thin-film transistor is 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 of the pixel capacitor, and has a channel layer formed with In—

Ga—

Zn—

O.

20. A method for driving a liquid crystal display device configured to display an image by applying alternating-current voltages to liquid crystals in accordance with externally inputted image data when performing pause drive with a pause frame for pausing screen refresh being set between two refresh frames in which screen refresh is performed, the method comprising the steps of:

detecting whether there is any state change of image data for a current frame;

upon detection of a state change of the image data for the current frame, determining whether the number of pause frames preceding the current frame is greater than a preset threshold;

when the number of pause frames is determined to be greater than the threshold, applying a boost charge voltage and an image signal voltage successively to the data signal lines, the boost charge voltage being different in polarity from image data for the pause frame and being based on correction image data obtained by subjecting the image data for the current frame to a tone emphasizing process for emphasizing a temporal change, the image signal voltage having the same polarity as the correction image data and being based on the image data for the current frame; and

when the number of pause frames is determined to be less than the threshold, applying the image signal voltage to the data signal lines, the image signal voltage being different in polarity from the image data for the pause frame.