KR101365796B1 - Liquid Crystal Display Device in Light Switching System and Driving Method thereof - Google Patents

Abstract

The present invention provides an optical intermittent liquid crystal display device suitable for displaying an image of maximum luminance while preventing the occurrence of motion blurring.

An optical intermittent liquid crystal display device includes at least one light source element for irradiating light onto a liquid crystal panel; A light receiving element for sensing the amount of light from the liquid crystal panel; A response time detector for detecting a response time of a liquid crystal pixel on the liquid crystal panel from the detection signal from the light receiving element; A brightness detector for detecting a brightness of an image displayed on the liquid crystal panel from the detection signal from the light receiving element; A dimming duty ratio determining unit configured to calculate a dimming duty ratio of the light source based on the detected response time and luminance of the liquid crystal; And a light source driver for causing the light source element to be turned on and off repeatedly according to the dimming duty ratio determined by the dimming duty ratio determining unit.

Dimming, duty ratio, lamp, luminance, motion, blurring, image quality

Description

Liquid Crystal Display Device in Light Switching System and Driving Method

1 is a block diagram illustrating an optical intermittent liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram for explaining the characteristics of the dimming duty ratio indicating the change of the MPRT in the form of nonlinear curves according to the liquid crystal response time.

BRIEF DESCRIPTION OF THE DRAWINGS

10: liquid crystal panel 12: gate driver

14: Data driver 16: Timing controller

18: backlight unit 20: light receiving element

22: response time detector 24: luminance detector

26: dimming duty ratio determining unit 28: duty ratio control unit

30: light source driving unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having a backlight switching function and a driving method thereof.

Conventional liquid crystal display devices can be made slimmer and lighter, but also facilitate the implementation of large screens. In addition, the liquid crystal display consumes small power. In this respect, instead of the conventional cathode ray tube display device, which is also referred to as a CRT, a liquid crystal display device is commonly used.

In a moving image displayed by a liquid crystal display, a motion blurring phenomenon in which the outline of an object is blurred appears. In order to prevent the occurrence of such motion blurring and ghosting, a method of controlling the light irradiated to the rear surface of the liquid crystal panel is applied to the liquid crystal display. In the liquid crystal display device of the light intermittent method, in order to minimize the deterioration of the brightness of the image due to light interruption, a light irradiation period (that is, a dimming duty ratio) for the light intermittent period (hereinafter, referred to as a "dimming duty ratio"). ""). The dimming duty ratio of the light irradiated onto the liquid crystal panel is a characteristic that is in contrast to the period from which the outline becomes blurry to clear again (ie, the motion picture response time (hereinafter referred to as "MPRT") and the brightness of the image). In other words, as the dimming duty ratio of the light irradiated onto the liquid crystal panel becomes smaller, the MPRT becomes better (shorter) while the brightness of the image is lowered.

However, the dimming duty ratio of the light irradiated to the liquid crystal causes the change characteristic of the luminance of the MTRT and the image to be deepened in accordance with the response speed of the liquid crystal. In fact, if the light is irradiated to the liquid crystal panel with 50% and 100% dimming duty ratio with the response speed of 5ms, 50% of the dimming duty ratio of the light is 5.3 MPT compared to 100% of the dimming duty ratio of the light. While shortening by ms, it reduces the brightness of the image by about 40%.

In order to increase the brightness of the image while preventing motion blur (i.e., maintaining the MPRT for less than a certain time), the dimming duty ratio of the light to be irradiated to the liquid crystal panel should be adjusted in consideration of the response speed of the liquid crystal. Nevertheless, the optical intermittent liquid crystal display adjusts the dimming duty ratio of the light to be irradiated onto the liquid crystal panel irrespective of the response speed of the liquid crystal. As a result, the liquid crystal display has no choice but to cause motion blur or reduce luminance of an image. In addition, the optical intermittent liquid crystal display device displays an image that causes the user to be tired due to a change in the response time of the liquid crystal according to the use time.

Accordingly, an object of the present invention is to provide an optical intermittent liquid crystal display device and a driving method thereof suitable for displaying an image of maximum luminance while preventing the occurrence of motion blurring.

Another object of the present invention is to provide a liquid crystal display and a driving method thereof suitable for displaying an image that a user can comfortably view.

According to an aspect of the present invention, there is provided an optical intermittent liquid crystal display device, including: at least one light source element for irradiating light onto a liquid crystal panel; A light receiving element for sensing the amount of light from the liquid crystal panel; A response time detector for detecting a response time of a liquid crystal pixel on the liquid crystal panel from the detection signal from the light receiving element; A brightness detector for detecting a brightness of an image displayed on the liquid crystal panel from the detection signal from the light receiving element; A dimming duty ratio determining unit configured to calculate a dimming duty ratio of the light source based on the detected response time and luminance of the liquid crystal; And a light source driver for causing the light source element to be turned on and off repeatedly according to the dimming duty ratio determined by the dimming duty ratio determining unit.

According to another aspect of the present invention, a method of driving an optical intermittent liquid crystal display device includes: sensing an amount of light from a liquid crystal panel; Detecting a response time of a liquid crystal pixel on the liquid crystal panel from the sensed light amount; Detecting a luminance of an image displayed on the liquid crystal panel from the detected amount of light; Calculating a dimming duty ratio of a light source for irradiating light onto the liquid crystal panel based on the response time and the luminance of the detected liquid crystal; And causing the at least one light source element to turn on and off repeatedly according to the determined dimming duty ratio.

Other objects, other features, and other advantages of the present invention will become apparent from the detailed description of the embodiments with reference to the attached drawings.

Best Mode for Carrying Out the Invention Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram illustrating a liquid crystal display of an optical switching method according to an exemplary embodiment of the present invention. Referring to FIG. 1, the liquid crystal display includes a gate driver 12 connected to a plurality of gate lines GL1 to GLn on the liquid crystal panel 10 and a plurality of data lines DL1 to on the liquid crystal panel 10. A data driver 14 connected to the DLm, and a timing controller 16 controlling these drivers 12,14. In the liquid crystal panel 10, a plurality of pixel regions arranged in an active matrix form are distinguished by crossing the gate lines GL1 to GLn and the data lines DL1 to DLm. A liquid crystal pixel is formed in each of the plurality of pixel regions.

The gate driver 12 sequentially enables a plurality of gate lines GL1 to GLn for one frame (period of one vertical synchronizing signal) sequentially by a predetermined period (for example, one horizontal synchronizing signal). Let's do it. To this end, the gate driver 12 generates a plurality of gate signals having exclusively enable pulses which are sequentially shifted for each period of the horizontal synchronization signal. The gate enable pulse included in each of the plurality of gate signals has the same width as the period of the horizontal synchronous signal. The enable pulse included in each of the plurality of gate scan signals is generated once every frame period. To generate these multiple gate scan signals, the gate driver 12 responds to gate control signals GCS from the timing controller 16. The gate control signals GCS include a gate start pulse GSP and at least one gate clock GSC. The gate start pulse GSP has a pulse of a specific logic (for example, high logic) corresponding to a period of one horizontal synchronization signal from the start of the frame period.

The data driver 14 corresponds to the number of data lines DL1 to DLm each time any one of the plurality of gate lines GL1 to GLn is enabled (that is, to the number of liquid crystal pixels arranged in one gate line). Generate pixel drive signals). Each pixel data signal for one line is supplied to a corresponding liquid crystal pixel on the liquid crystal panel 10 via a corresponding data line DL. Each of the liquid crystal pixels arranged on the gate line GL passes an amount of light corresponding to a voltage level of the pixel driving signal. In order to generate the pixel drive signal for one line, the data driver 14 responds to the data control signal DCS and, in response to the data control signal DCS, one line of pixel data VDd for each period of the enable pulse included in the gate signal. Enter sequentially. The data driver 14 simultaneously converts sequentially input pixel data VDd for one line into pixel drive signals in analog form.

The timing controller 16 inputs the synchronization signals SYNC from an external video source (for example, an image demodulation module included in a television receiver or a graphics module included in a computer system) not shown. The sync signals SYNC include a data clock Dclk, a data enable signal DE, a horizontal sync signal Hsync, a vertical sync signal Vsync, and the like. The timing controller 16 causes the gate driver 12 to sequentially scan the plurality of gate lines GL1 to GLn on the liquid crystal panel 10 every frame using the synchronization signals SYNC. The gate control signals GCS required to generate the plurality of gate signals are generated. In addition, the timing controller 16 sequentially inputs one line of pixel data VDd to the data driver 12 every cycle in which the gate line GL is enabled, and sequentially inputs one line of pixel data VDd. The data control signals DCS are required to convert the pixel data VDd into an analog pixel data signal and output the same. Further, the timing controller 16 inputs a pixel data stream VDf divided in units of frames (one image unit) from a video source. The timing controller 16 divides the pixel data stream VDf for each frame into the pixel data stream VDd for each line and divides the pixel data stream VDd for the divided line to the data driver 14. Supply.

The liquid crystal display of FIG. 1 includes a backlight unit 18 positioned below the liquid crystal panel 10 and a light receiving element 20 positioned on the liquid crystal panel 10. The backlight unit 18 irradiates planar light to the rear surface of the liquid crystal panel 10. To this end, the backlight unit 18 includes at least one light source element. The light receiving element 10 is provided so as to correspond to any one liquid crystal pixel on the liquid crystal panel 10. The light receiving element 10 converts the amount of light from the corresponding liquid crystal pixel into an electrical signal. The electrical signal converted by the light receiving element 20 is supplied to the response time detector 24 and the luminance detector 26 as a light detection signal.

The response time detector 22 is a response time of a liquid crystal pixel (ie, a liquid crystal cell) on the liquid crystal panel 10 based on a time and a change in the light sensing signal from the light receiving element 20 (hereinafter referred to as "liquid crystal response time"). Detection). To this end, the response time detector 22 detects the minimum voltage (or current) level and the highest voltage level of the light sensing signal. The response time detector 22 counts the time that the light sensing signal has passed from the minimum (highest) voltage level to the highest (minimum) voltage level. The counted time is output from the response time detector 22 as the liquid crystal response time.

The brightness detector 26 detects the brightness of the image displayed on the liquid crystal panel 10 from the light detection signal from the light receiving element 20. To this end, the luminance detector 26 integrates the voltage (or current) of the light sensing signal and converts the integrated voltage (current) into digital integrated voltage data. The integrated voltage (or current) data thus converted is used as luminance data displayed on the liquid crystal panel 10.

The dimming duty ratio determiner 26 includes at least one light source element included in the backlight unit 18 based on the liquid crystal response time from the response time detector 22 and the luminance data from the luminance detector 24. For example, the dimming duty ratio of the lamp or light emitting diode) is determined. To this end, the dimming duty ratio determiner 26 first searches for a range of dimming duty ratios applicable in the dimming duty ratio threshold (or inflection) information table using the liquid crystal response time LCRT. In the dimming duty ratio threshold (or inflection) table, the upper and lower threshold (inflection) values of the range of dimming duty ratios applicable for each liquid crystal response time (i.e., the luminance can be maintained while preventing occurrence of motion blurring). Are recorded. These upper and lower threshold values are determined by the characteristics of the dimming duty ratio indicating the change in MPRT in the form of nonlinear curves as the liquid crystal response time becomes longer as in FIG. 2.

As can be seen in FIG. 2, the MPRT becomes nonlinearly longer according to the liquid crystal response time as the dimming duty ratio is smaller. For example, when the light source element in the backlight unit 18 irradiates light onto the liquid crystal panel 10 with a 60% dimming duty portion, the MPRT is 10.4 ms when the liquid crystal response time is 11 ms, but the liquid crystal response time is 12 ms. MPRT is rapidly increased to 15.7ms when. When the light source element in the backlight unit 18 irradiates light onto the liquid crystal panel 10 with a dimming duty of 70%, the MPRT is 11.8 ms when the liquid crystal response time is 10 ms, but the MPRT is 11 ms when the liquid crystal response time is 11 ms. It is rapidly lengthened to 15.6ms. Even when the light source element in the backlight unit 18 irradiates light onto the liquid crystal panel 10 with an 80% dimming duty portion, the MPRT is 11.9 ms when the liquid crystal response time is 8 ms, but the MPRT when the liquid crystal response time is 10 ms. Is drastically lengthened to 15.5ms. In other words, the response time value (critical response time value or inflection response time value) of the liquid crystal appears which causes the MPRT to increase rapidly discontinuously. When the liquid crystal response time is longer than this threshold response time (or the inflection response time), the MPRT changes rapidly. In addition, the threshold response time of the liquid crystal depends on the dimming duty ratio. Accordingly, in the dimming duty ratio threshold table, upper and lower dimming duty ratios representing the range of dimming duty ratios applicable according to the liquid crystal response time (i.e., the luminance can be maintained while preventing the occurrence of motion blurring). Is recorded.

In addition, the dimming duty ratio determiner 26 calculates a difference between the detected luminance data and the reference luminance value (that is, the target luminance value), and the dimming increases or decreases the luminance by the difference calculated in consideration of the MPRT. Determine the duty ratio. For example, if the detected liquid crystal response time is 9 ms, the dimming duty ratio determiner 26 searches for a range of the applicable 60% to 70% dimming duty ratio, and the luminance data detected in consideration of the MPRT within the detected range. Determine a dimming duty ratio that can cause the luminance to be increased by a difference between and the target luminance value.

The duty ratio control unit 28 and the light source driver 30 are connected between the dimming duty ratio determining unit 26 and the backlight unit 18. The duty ratio controller 28 may determine a specific logic corresponding to the dimming duty ratio for each constant period (eg, a vertical synchronization signal period) based on the dimming duty ratio from the dimming duty ratio determiner 26. Logic) to generate a light source control signal having an enable pulse. The period of the light source control signal coincides with the period of the vertical synchronizing signal, and the width of the enable pulse included therein coincides with the period corresponding to the dimming duty ratio with respect to the period of the vertical synchronizing signal. This light source control signal causes the at least one light source element in the backlight unit 18 to light up during the period of the enable pulse. In order to generate such a light source control signal, the duty ratio controller 28 includes a programmable pulse generator.

If the plurality of light source elements are arranged in the vertical direction in the backlight unit 18, the duty ratio controller 28 may generate light source control signals corresponding to the number of the light source elements. In this case, the plurality of light source control signals each have enable pulses shifted in phase by a predetermined period (for example, by 50 horizontal synchronization signals). Accordingly, the plurality of light source elements in the backlight unit 18 are sequentially turned on every predetermined period (i.e., the period corresponding to the 50 horizontal synchronization signals) to be turned off when the period corresponding to the dimming duty ratio has elapsed. Will be repeated. In order to generate the plurality of light source control signals, the duty ratio controller 28 may include a plurality of programmable pulse generators.

The light source driver 30 causes the light source element in the backlight unit 18 to be turned on and off in response to the light source control signal from the duty ratio controller 28. To this end, the light source driver 30 supplies the light source driving signal to at least one light source in the backlight unit in the period of the enable pulse included in the light source control signal. On the other hand, in the period in which the light source control signal maintains the basis logic (for example, low logic), the light source driver 30 blocks the light source driving signal to be supplied to the light source so that the light source element is turned off.

In this way, since the lighting period (dimming duty ratio) of the light source element is adjusted based on the liquid crystal response speed and the luminance, the motion blurring is minimized and the highest luminance can be maintained in the image displayed on the liquid crystal panel. As a result, the liquid crystal display device of the optical interruption system according to the present invention can display a good image. In addition, even if the response time of the liquid crystal pixel on the liquid crystal panel 10 changes, the dimming duty ratio is adjusted to adapt to the change. Accordingly, the liquid crystal panel 10 displays an image that can be easily recognized (viewed) by the user.

The response time detector 22, the luminance detector 24, and the dimming duty ratio determiner for adjusting the dimming duty ratio may be driven at the time of initial driving of the liquid crystal panel and at a predetermined time after the driving. This is due to the change in the response time of the liquid crystal as the driving period becomes longer at the initial stage of driving. The driving timing of the response time detector 22, the luminance detector 24, and the dimming duty ratio determiner 26 may be controlled by a timing control signal from the timing controller 16. As the response time detector 22, the luminance detector 24, and the dimming duty ratio determiner 26 are driven at regular intervals, power consumption may be reduced.

As described above, in the optical intermittent liquid crystal display according to the exemplary embodiment of the present invention, the lighting period (dimming duty ratio) of the light source element is adjusted based on the liquid crystal response speed and the luminance. Accordingly, in the image displayed on the liquid crystal panel, the highest luminance can be maintained while the motion blurring is suppressed. As a result, the liquid crystal display device of the optical interruption system according to the present invention can display a good image. In addition, even if the response time of the liquid crystal pixel on the liquid crystal panel changes, the dimming duty ratio is adjusted to adapt to the change. Therefore, the liquid crystal display device of the light intermittent method according to the present invention can display an image that can be easily recognized (viewed) by the user.

As described above, the present invention has been described with reference to the embodiment illustrated in FIG. 1, but a person having ordinary knowledge in the technical field to which the present invention belongs does not depart from the spirit and scope of the present invention. And it will be apparent that other equivalent embodiments are possible. Therefore, the technical scope and features of the present invention should not be limited to the description of the embodiments but should be set by the matters described in the appended claims.

Claims (8)

At least one light source element for irradiating light onto the liquid crystal panel; A light receiving element for sensing the amount of light from the liquid crystal panel; A response time detector for detecting a response time of a liquid crystal pixel on the liquid crystal panel from the detection signal from the light receiving element; A brightness detector for detecting a brightness of an image displayed on the liquid crystal panel from the detection signal from the light receiving element; A dimming duty ratio determining unit configured to calculate a dimming duty ratio of the light source element based on the detected response time and luminance of the liquid crystal; And a light source driving unit for causing the light source element to be turned on and off in accordance with the dimming duty ratio determined by the dimming duty ratio determining unit. The method of claim 1, wherein the dimming duty ratio determiner Determine the range of the applicable dimming duty ratio based on the response time of the liquid crystal, And a dimming duty ratio is selected from among values of the dimming duty ratio based on the detected luminance and reference luminance of the image. The method of claim 2, And the light receiving element is installed to correspond to any liquid crystal pixel on the liquid crystal panel. The method of claim 1, The at least one light source element comprises two or more lamps, And the light source driver drives two or more lamps sequentially to light up. Sensing the amount of light from the liquid crystal panel; Detecting a response time of a liquid crystal pixel on the liquid crystal panel from the sensed light amount; Detecting a luminance of an image displayed on the liquid crystal panel from the detected amount of light; Calculating a dimming duty ratio of a light source for irradiating light onto the liquid crystal panel based on the response time and the luminance of the detected liquid crystal pixel; And And causing the at least one light source element to be repeatedly turned on and off in accordance with the calculated dimming duty ratio. The method of claim 5, wherein the dimming duty ratio calculation step, Determining a range of applicable dimming duty ratios based on a response time of the liquid crystal pixel; And And selecting one of the values of the dimming duty ratio as a dimming duty ratio based on the detected luminance and a reference luminance of the image. The method of claim 6, Detecting the amount of light from the liquid crystal panel, And sensing the amount of light from any liquid crystal pixel on said liquid crystal panel. The method of claim 7, wherein According to the calculated dimming duty ratio, causing the at least one light source element to be repeatedly turned on and off, And a method of driving an optical intermittent liquid crystal display in which two or more lamps included in the at least one light source element are sequentially turned on.

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