# US 9,520,097 B2 · Display device with compensating backlight drive circuit and method for driving same

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- Number: US 9,520,097 B2
- Document ID: US9520097B2
- Status: Granted
- Kind: B2
- Application number: 14/351,613
- Filed: 2012-10-31
- Published: 2014-09-18
- Granted: 2016-12-13
- Earliest claimed: 2011-11-07
- Assignees: Sharp Kabushiki Kaisha
- Applicants: Sharp Kabushiki Kaisha
- Inventors: Yutaka Takamaru; Seiji Kaneko; Yasuyuki Ogawa; Kaoru Yamamoto; Kohhei Tanaka; Seiichi Uchida; Noriaki Yamaguchi; Shigeyasu Mori
- Web page: https://patentgrep.com/patent/US9520097B2

## CPC

- G09G 3/3648: {using an active matrix (G09G3/367 - G09G3/3696 take precedence)}
- G09G 3/3406: {Control of illumination source (illumination devices structurally associated with liquid crystal cells G02F1/1336)}
- G09G 3/3614: {Control of polarity reversal in general}
- G09G 2310/0237: Switching ON and OFF the backlight within one frame
- G09G 2320/0247: Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
- G09G 2320/0626: for control of overall brightness
- G09G 2360/16: Calculation or use of calculated indices related to luminance levels in display data
- G09G: ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION (arrangements for transferring data between digital computers and displays G06F3/14; static indicating arrangements comprising an association of a number of separate sources or light control cells G09F9/00; static indicating arrangements comprising integral associations of a number of light sources H01J, H01K, H10H, H05B33/12; scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission, details thereof H04N1/00)

## Abstract

In a display control circuit (200) of a display device, an image pattern detection portion (230) detects whether an image is an anti-flicker pattern or not, and when it is an anti-flicker pattern, a backlight source is driven (typically, such that its luminance changes in the opposite phase relative to luminance changes that would occur), on the basis of predicted values, which are predetermined so as to compensate for the luminance changes that would occur. Moreover, the backlight is not turned on during the scanning period. As a result, flicker due to current leakage, etc., can be reduced or eliminated in a display device for which a scanning period and a scan stop period are set.

## Claims

### Claim 1

An active-matrix display device provided with a backlight including a light source, a plurality of pixel forming portions for forming an image to be displayed by transmitting light from the light source, a plurality of video signal lines for transmitting a plurality of video signals representing the image to be displayed to the pixel forming portions, and a plurality of scanning signal lines crossing the video signal lines, the pixel forming portions being arranged in a matrix so as to be associated with the video signal lines and the scanning signal lines, the device comprising:
a scanning signal line driver circuit for selectively driving the scanning signal lines during a predetermined scanning period and deselecting all of the scanning signal lines during a hold off period starting upon completion of the scanning period, the scanning period and the hold off period constituting a frame period longer than 1/60 of a second;
a video signal line driver circuit for providing the video signal lines with the video signals to be transmitted, during the scanning period;
a backlight drive circuit for controlling the light source included in the backlight so as to be turned on/off multiple times during the hold off period; and
a luminance change storage portion having prestored therein predicted values for luminance changes due to current leakage in an image displayed by the pixel forming portions during the hold off period, wherein,
the backlight drive circuit calculates emission luminance of the light source multiple times during the hold off period on the basis of the predicted values stored in the luminance change storage portion, and controls the light source so as to be turned on with the calculated emission luminance, thereby compensating for the luminance changes.

### Claim 2 (depends on 1)

The display device according to claim 1, further comprising a pattern detection portion for determining whether or not at least a part of the image matches a prestored display pattern, wherein,
the luminance change storage portion has stored therein predicted values for luminance changes corresponding to display patterns detectable by the pattern detection portion, and
when the pattern detection portion determines a match, the backlight drive circuit calculates and controls the emission luminance of the light source on the basis of predicted values stored in the luminance change portion and corresponding to a display pattern determined as the match.

### Claim 3 (depends on 2)

The display device according to claim 2, wherein,
the video signal line driver circuit performs drive such that the video signals transmitted to the pixel forming portions are inverted in polarity every frame period and also every one or more rows corresponding to one or more scanning signal lines, and
the pattern detection portion detects a display pattern in which display tone values change regularly every row for which the polarity inversion is performed by the video signal line driver circuit.

### Claim 4 (depends on 3)

The display device according to claim 3, wherein,
the video signal line driver circuit performs drive such that the video signals transmitted to the pixel forming portions are inverted in polarity every one or more columns corresponding to one or more video signal lines, and
the pattern detection portion detects a display pattern in which display tone values change regularly every row and column for which the polarity inversion is performed by the video signal line driver circuit.

### Claim 5 (depends on 4)

The display device according to claim 4, wherein,
the luminance change storage portion has stored therein predicted values for luminance changes corresponding to display patterns to be presented alternatingly with predetermined first and second display tone values every row and column for which the polarity inversion is performed by the video signal line driver circuit, and
the pattern detection portion detects a display pattern to be presented alternatingly with the first display tone values or neighborhood values thereof and the second display tone values or neighborhood values thereof every row and column for which the polarity inversion is performed by the video signal line driver circuit.

### Claim 6 (depends on 1)

The display device according to claim 1, wherein the backlight drive circuit performs control such that an operation of turning on and then off the light source within a time period shorter than 1/60 of a second is performed once or more during the hold off period.

### Claim 7 (depends on 6)

The display device according to claim 6, wherein the backlight drive circuit performs control such that an operation of turning on and then off the light source so as to be kept off for a time period longer than a time period that extends from the time of turning on to the following turning off is performed once or more.

### Claim 8 (depends on 1)

The display device according to claim 1, wherein the backlight drive circuit performs control such that the light source is off during the scanning period.

### Claim 9 (depends on 8)

The display device according to claim 8, wherein the backlight drive circuit performs control such that the light source is maintained in off state for a predetermined time period immediately after completion of the scanning period.

### Claim 10 (depends on 2)

The display device according to claim 2, wherein,
the backlight drive circuit divides an input image into a plurality of areas, and obtains emission luminance data indicating emission luminance of the light source for each of the areas, on the basis of the input image,
the video signal line driver circuit determines potentials of the video signals to be transmitted, on the basis of the emission luminance data,
the pattern detection portion detects the display pattern for each of the areas, and
the backlight drive circuit calculates and controls the emission luminance of the light source for each of the areas including a display pattern determined as a match by the pattern detection portion, on the basis of predicted values stored in the luminance change portion and corresponding to the display pattern determined as the match.

### Claim 11 (depends on 1)

The display device according to claim 1, wherein,
each of the pixel forming portions includes:
a thin-film transistor that is rendered conductive or non-conductive in accordance with a signal applied to a scanning signal line connected thereto;
a pixel electrode connected to the video signal line via the thin-film transistor;
a common electrode provided commonly for the pixel forming portions;
pixel capacitance created by the pixel electrode and the common electrode; and
a liquid crystal element for displaying a pixel with a display tone corresponding to a voltage held in the pixel capacitance, wherein,
the thin-film transistor includes a semiconductor layer made of an oxide semiconductor.

### Claim 12

A method for driving an active-matrix display device provided with a backlight including a light source, a plurality of pixel forming portions for forming an image to be displayed by transmitting light from the light source, a plurality of video signal lines for transmitting a plurality of video signals representing the image to be displayed to the pixel forming portions, and a plurality of scanning signal lines crossing the video signal lines, the pixel forming portions being arranged in a matrix so as to be associated with the video signal lines and the scanning signal lines, the method comprising:
a scanning signal line drive step of selectively driving the scanning signal lines during a predetermined scanning period and deselecting all of the scanning signal lines during a hold off period starting upon completion of the scanning period, the scanning period and the hold off period constituting a frame period longer than 1/60 of a second;
a video signal line drive step of providing the video signal lines with the video signals to be transmitted, during the scanning period; and
a backlight drive step of controlling the light source included in the backlight so as to be turned on/off multiple times during the hold off period, wherein,
in the backlight drive step, emission luminance of the light source is calculated multiple times during the hold off period on the basis of prestored predicted values for luminance changes due to current leakage in an image displayed by the pixel forming portions during the hold off period, and the light source is controlled so as to be turned on with the calculated emission luminance, thereby compensating for the luminance changes.