KR20140093467A - Liquid Crystal Display Device And Driving Method Thereof - Google Patents

Abstract

The present invention relates to a liquid crystal display device and a driving method thereof capable of reducing the consumption of electrical power by performing a dimming control without the degradation of sensory quality of an image in a bright screen with brightness greater than the specific brightness. The liquid crystal display device according to the present invention comprises; a liquid crystal panel which displays the image; a back light unit which supplies light for displaying the image to the liquid crystal panel; a driving circuit which controls the drive of the liquid crystal panel or the back light unit to display the image, and supplies a control signal including an image signal to the liquid crystal panel; and a dimming control unit which performs a dimming control including a light output control of the back light unit by controlling the driving circuit if the brightness of the image is over the predetermined standard brightness.

Description

[0001] The present invention relates to a liquid crystal display device,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a driving method thereof, and more particularly, to a liquid crystal display device and a method of driving the same, in which power consumption can be reduced by performing dimming control without deteriorating visual perception quality .

A liquid crystal display, which is one of the flat panel display devices, is capable of displaying a high image quality, can be driven at low power, is easily manufactured in various screen sizes, is used in various fields, and is exposed to various environments.

Such a liquid crystal display device requires a backlight unit for expressing an image, and the liquid crystal panel displays an image by adjusting the amount of light transmitted from the backlight unit.

Therefore, the specific gravity of the power consumption of the liquid crystal display device is large because the specific gravity of the power required for driving the backlight unit is large, and the image quality is also dependent on the degree of utilizing the light from the backlight unit.

Accordingly, a driving method of a liquid crystal display device includes a dimming control method for improving picture quality and reducing power consumption. The dimming control is performed in such a manner that the driving amount of the backlight, that is, the light supply amount is adjusted by analyzing the image of the whole or part of the screen and the gain value is adjusted to the analyzed part of the image. This dimming control has the effect of reducing the power consumption or increasing the contrast ratio while outputting the same brightness image as before. Therefore, even in the same liquid crystal display device, the liquid crystal display device driven by the dimming control can display a higher-quality image and is driven by low power consumption.

However, in such a conventional dimming control method, the effect of dimming control becomes small when a bright screen is continuous. Specifically, the dimming control method mainly uses a method of determining the image and driving the backlight unit, that is, reducing the supply of light, while increasing the gain and outputting an image of the same brightness as a result. However, in the case of the bright screen, the compensation due to the increase of the gain is not performed well, but the light supply by the backlight unit is reduced, so that the desired dimming control is difficult.

Therefore, when the dimming control is performed on a bright screen, the image quality deteriorates and the quality of the image perceived by the user deteriorates. In addition, when the dimming control on the bright screen is canceled in order to solve this problem, there arises a problem that the power reduction effect is lowered in a high-power-consuming image.

It is therefore an object of the present invention to provide a liquid crystal display device and a method of driving the same that enable dimming control and diminish power consumption without deteriorating visual perception quality even on a bright screen over a certain luminance.

According to an aspect of the present invention, there is provided a liquid crystal display comprising: a liquid crystal panel displaying an image; A backlight unit for supplying light to the liquid crystal panel for displaying the image; A driving circuit for controlling driving of the liquid crystal panel or the backlight unit for displaying the image and supplying a control signal including a video signal to the liquid crystal panel; And a dimming control unit controlling the driving circuit to perform dimming control including adjustment of an optical output of the backlight unit when the brightness of the image is equal to or greater than a predetermined reference brightness.

The dimming control reduces the light output of the backlight unit by a predetermined output reduction amount continuously in accordance with a lapse of time or a change of a frame for displaying the image.

The dimming control unit performs the dimming control when the image by the video signal is a dynamic image.

The dimming control unit performs dimming control when the luminance difference between the previous frame and the current frame is equal to or less than a predetermined luminance difference value.

The dimming control unit reduces the light output of the backlight unit within a luminance range of a predetermined lower luminance limit value or more.

The dimming control increases the gain of the video signal in correspondence with the reduction of the light output of the backlight unit.

According to another aspect of the present invention, there is provided a method of driving a liquid crystal display, comprising: supplying a video signal for displaying an image from the outside; Calculating a luminance of the image from the video signal by the dimming control unit; The dimming control unit comparing the brightness of the image with a predetermined reference brightness; A dimming control step in which the dimming control unit adjusts an optical output of the backlight unit when the brightness of the image is equal to or greater than the reference brightness; And a liquid crystal panel and a driving unit displaying an image using the image signal by the dimming control; .

In the dimming control step, the dimming control unit reduces the light output of the backlight unit by a predetermined output reduction amount in accordance with a lapse of time or a change of a frame for displaying the image.

Wherein the step of supplying the control signal or the step of calculating the brightness of the image includes the step of determining whether the image based on the image signal is a dynamic image, and the dimming control unit is operable, when the image is a dynamic image, Control step.

Wherein the dimming control step comprises the step of the dimming control unit comparing the brightness of the previous frame with the brightness of the current frame, and if the brightness difference between the previous frame and the current frame is equal to or less than a predetermined brightness difference value, do.

The dimming control unit reduces the light output of the backlight unit within a luminance range of a predetermined lower luminance limit value or more.

The dimming control step increases the gain of the video signal in response to the reduction of the optical output of the backlight unit.

The dimming control unit performs global dimming when the brightness is equal to or less than the reference brightness value.

The liquid crystal display device and the driving method thereof according to the present invention can reduce power consumption by performing dimming control without deteriorating the visual perception quality even on a bright screen over a certain luminance.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram showing a configuration of a liquid crystal display device according to the present invention; Fig.
Fig. 2 is a diagram illustrating a configuration example of a sub-pixel circuit of the liquid crystal panel shown in Fig. 1; Fig.
3 is a flowchart showing a driving method of a liquid crystal display according to the present invention.
4 is a graph showing the relationship between the light output and the luminance of an image according to the dimming control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. It should be noted that the drawings denoted by the same reference numerals in the drawings denote the same reference numerals whenever possible, in other drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. And certain features shown in the drawings are intended to be illustrative, not limiting, or reduced, or simplified, and the drawings and elements thereof are not necessarily drawn to scale. However, those skilled in the art will readily understand these details.

Fig. 1 is a schematic diagram showing a configuration of a liquid crystal display device according to the present invention, and Fig. 2 is a diagram showing a configuration example of a subpixel circuit of the liquid crystal panel shown in Fig.

1, a liquid crystal display device according to the present invention includes a liquid crystal panel 10, a timing control unit 20, a dimming control unit 30, a data driving unit 40, a gate driving unit 50, a backlight driving unit 60, And a backlight unit (70).

The liquid crystal panel 10 is driven by a data signal and a gate signal supplied from the data driver 40 and the gate driver 50 to display an image. To this end, the liquid crystal panel 10 includes an upper substrate, a lower substrate, and a liquid crystal layer formed between the upper substrate and the lower substrate. Data lines DL1 to DLn connected to the data driver 40 and gate lines SL1 to SLm connected to the gate driver 50 are connected to the substrate constituting the liquid crystal panel 10 in a matrix form. And a subpixel SP is formed at the intersection of the gate line Sl and the data line DL. The subpixel SP may include a thin film transistor (TFT), a liquid crystal cell CL and a storage capacitor Cst as shown in FIG. In the subpixel SP, two or more pixels form one pixel, and the color represented by each subpixel is divided into red (R), green (G), and blue (B) by a color filter formed on the substrate The present invention is not limited thereto. In addition, a black matrix layer polarizing layer may be further formed on the substrate. The liquid crystal panel 10 may include an electrode, a color filter, a black filter, and the like according to a vertical electric field system such as TN (Twisted Nematic) or VA (Vertical Alignment), a horizontal electric field system such as IPS (In Plane Swing) Matrix, and subpixel may be varied, and the present invention is not limited by the presented examples.

The timing control unit 20 receives the video signal ADATA, the clock signal DC, the enable signal DE, the vertical synchronization signal Vs and the horizontal synchronization signal Hs from the outside, And the gate driver 50. [ Particularly, the timing controller 20 transmits the video data DDATA controlled by the dimming control signal Cdata from the dimming control unit 30 to the data driver 40. Such dimming control will be described in more detail below. The timing controller 20 controls the operation timing of the data driver 40 and the gate driver 50 using the vertical synchronization signal Vs, the horizontal synchronization signal Hs, the enable signal DE and the clock signal DC . The control signal generated from the timing control unit 20 may include a gate control signal GDC for controlling the driving of the gate driving unit 50 and a data control signal DDC for controlling the driving of the data driving unit 40 have.

The data driver 40 samples and latches a digital video signal supplied from the timing controller 20, particularly, the video data DDATA subjected to the dimming control in response to the data control signal DDC supplied from the timing controller 20, Into data of a data structure. For this, the data driver 40 may include a shift register, a latch, a converter, and the like.

The gate driver 50 generates a gate driving voltage in response to the gate control signal GDC supplied from the timing controller 920 and supplies the generated gate driving voltage through the gate line SL. For this, the gate driver 50 may include a shift register, a level shifter, and an output buffer.

The backlight unit 70 operates under the control of the backlight driver 60 to generate light and supply the generated light to the liquid crystal panel 10. [ The backlight unit 70 is disposed below the liquid crystal panel 10 and includes a light source such as an LED (Light Emitting Diode), a CCFL (Cold Cathode Fluorescent Lamp), an EEFL (External Electrode Fluorescent Lamp) And an optical configuration such as a reflective sheet. The light source of the backlight unit 70 supplies light to the liquid crystal panel 10 by varying the light output according to the backlight control signal BL supplied from the backlight driver 60.

The backlight driver 60 supplies the backlight control signal BL including the driving voltage for driving the backlight unit 70 to the backlight unit 70. [ The backlight control signal BL may include a light control signal for the points of the light source and a signal for adjusting the light amount of the light source. In particular, the backlight driver 60 may supply a PWM voltage signal (Pulse Width Modulation) signal to easily adjust the amount of backlight, but the present invention is not limited thereto. In particular, the backlight driver 60 receives the output control signal BLC from the timing controller 20 and adjusts the light output of the backlight unit 70 accordingly.

The dimming control unit 30 performs dimming control of an image displayed by the liquid crystal panel 10. [ Specifically, the dimming control unit 30 determines the brightness of the image through the external image signal ADATA, and performs dimming control according to the determination result. For this, the dimming control unit 30 transmits a control signal for adjusting the gain to the timing controller 20 according to the determination result, or transmits the gain-adjusted image data CDATA to the timing controller 20 according to the dimming control . In the following description, the dimming control unit 30 transmits the image data CDATA whose gain has been adjusted according to the dimming control to the timing control unit 20, so that the description will proceed. However, this is for convenience of explanation and does not limit the present invention. The dimming control unit 30 transmits an output control signal BLC for controlling the light output of the backlight unit 70 to the backlight driving unit 60 according to the judgment of the image. To this end, the dimming control unit calculates an average picture level (APL), determines whether the bright image is continuous, determines whether the continuous bright image is a dynamic image, . This will be described in more detail below with reference to a separate drawing.

FIG. 3 is a flowchart illustrating a method of driving a liquid crystal display according to the present invention, and FIG. 4 is a graph illustrating a luminance relationship between an optical output and an image according to dimming control.

3 to 5, a driving method of a liquid crystal display (LCD) device according to the present invention includes a video signal supply step S10, an APL calculation step S20, a brightness comparison step S30, a dimming control step S40, And an output step S50.

The signal supply step S10 is a step of supplying the image data ADATA, the vertical synchronizing signal VS, the horizontal synchronizing signal HS, the clock signal DC and the enable signal DE to display an image through the liquid crystal panel 10 Is supplied to the timing control unit 20. The timing control unit 20 may be a microcomputer. In the signal supply step S10, the video data ADATA is supplied to the dimming control unit 30. [

The APL calculation step S20 is a step in which the dimming control unit 30 calculates the average picture level (APL) for judging whether or not the dimming control is applied from the video data ADATA. At this time, the dimming control unit 30 calculates the average value of the brightness for each pixel of the entire screen. Here, one pixel is composed of a plurality of subpixels SP, and the representative luminance of the pixel, i.e., the luminance used for calculating the average, is the luminance value of the plurality of subpixels SP constituting one pixel The pixel value of the entire screen is calculated using the highest value. At this time, the APL calculation is performed for each frame or for an image at a constant time interval.

The luminance comparison step S30 compares the APL value calculated in the previous step, in particular, the luminance value and the reference luminance value, and determines whether the image to be output is a bright image designated by the manufacturer. Also, in the brightness comparing step S30, it may be configured to further include a step of comparing brightness between the current frame and the previous or subsequent frame, and determining whether the image to be output is one frame of the dynamic image. If the image to be output in the brightness comparison step S30 is determined to be a bright image, the dimming control unit 930 determines that the target image is a dimming control image, and the dimming control step S40 is performed. Otherwise, the image output step S50 is performed It proceeds.

The dimming control step S40 is a step of performing dimming control when the image to be output in the brightness comparing step S30 is in conformity with the dimming control condition. Specifically, the dimming control step (S40) of the present invention is performed by distinguishing a bright screen over the reference brightness and a relatively dark screen below the reference brightness. Particularly, since dimming by global dimming or local dimming is hardly performed on a bright screen, in the present invention, power consumption is reduced by continuously reducing the brightness at a level that the viewer can not perceive. For this purpose, in the dimming control step S40, it is determined whether the dimming control condition is satisfied, and accordingly, the output of the backlight unit is continuously reduced by the output reduction amount of the predetermined backlight unit. Through this, the user can not recognize the decrease in the luminance between the frames, but when the dimming of several frames proceeds, the backlight output is significantly reduced as compared with the screen before the dimming control. In particular, in the dimming control step S40, dimming control is performed on a bright image having a reference brightness. In this case, if the output of the backlight unit is reduced in the still image, since the user can recognize that the brightness of the image is lowered, the dimming control is performed only for the dynamic image. If the continuous bright image is the dynamic image, The output of the backlight unit is continuously reduced by the predetermined output reduction amount according to the time, thereby reducing the power consumption. This will be described in more detail with reference to FIG. 4 below. Meanwhile, the dimming control step S40 proceeds so that the output of the backlight unit does not decrease below a predetermined lower limit value even if the dynamic image advances for a long time. Also, when the backlight output is decreased, the image data DDATA supplied to the liquid crystal panel may be data with increased gain.

The video output step S50 is a step in which the liquid crystal panel displays an image by the video data. The video output step S50 may be an image having an average luminance equal to or higher than the reference luminance, and the dimming control for the bright image in the dimming control step S40 may be performed. Alternatively, the image data having the average luminance of the reference luminance binomial may be an image in which global dimming or local dimming control is performed instead of dimming control for a bright image.

FIG. 4 is a graph showing the relationship between the light output and the brightness of the image according to the dimming control, and Table 1 is a table showing the power consumption reduction when the dimming condition is changed.

division Set 1 Set 2 Set 3 Set 4 Condition 1 10 10 20 20 Condition 2 200 100 100 80 Condition 3 100 100 100 100 Dimming control ON 31.62w / h 31.08w / h 30.04w / h 29.46w / h Dimming control OFF 31.62w / h 31.62w / h 31.62w / h 31.62w / h GD OFF 47.7 w / h 47.7 w / h 47.7 w / h 47.7 w / h

Referring to FIG. 4 and Table 1, the dimming control according to the present invention is performed according to whether a bright image over a reference brightness, a bright image lasts, or a bright image is a dynamic image. For this, the reference luminance (B_lu), which is a criterion of the bright image, is compared with the luminance of the previous frame and the current frame to check whether the bright image is continuous. Also, when the output of the backlight unit continues to decrease, a bright image may be converted into a dark image, and thus the lower limit of the output reduction is obtained. The values for determining the reference brightness, the lower limit value, and the continuity of the bright image can be set by the user, and the power saving effect is different depending on the setting of these values. Here, the determination of continuity of the bright image may be used to determine whether the output image is a bright image and whether the output image is a dynamic image. In addition, the method of determining whether the output image is a dynamic image or a still image can be judged by using the inter-frame comparison algorithm of the image data in addition to the continuity of the bright image, and a detailed description thereof will be omitted.

Table 1 shows the degree of power saving according to the conditions by setting these conditions differently.

Concretely, Condition 1 sets the output reduction of the backlight unit during dimming control, and is used as a value obtained by multiplying the table value by a predetermined constant value (for example, 32). That is, when the predetermined constant value is 32, when the condition 1 is set to 10, the output reduction of the backlight unit is 320 at one time, and becomes 640 at 20. The values 320 and 640 may be brightness values that are set in a constant range such as 0 to 3000. [

Condition 2 is a reference luminance value, and an image having an average luminance equal to or higher than a predetermined value is determined as a bright image.

Condition 3 is a lower limit value of the luminance reduction when the backlight output is reduced, and the limiting value is such that the backlight output reduction by the dimming control is performed only over the luminance presented.

Table 1 shows the change in the amount of output when global dimming or local dimming is not performed. As shown in Table 1, when the dimming control of the present invention is performed with a constant output lowering limit value, a relatively low luminance is set to widen the range of the bright screen and the output reduction is increased (set 4) It can be confirmed that it is reduced. That is, it is possible to confirm that the power consumption is reduced only by changing the output decrement of the backlight unit continuously reduced in the dimming control, as in the case of the set 2 and the set 3, It can be seen that the power consumption differs even when the reference value of the bright image is different as in the comparison between the set 1 and the set 2.

4, the curve p indicates the average luminance of the image data, the vertical axis indicates the output of the backlight unit, and the horizontal axis indicates the luminance. In the horizontal axis, B-Lu is a reference luminance, and a region above this value is determined as a bright image and is subjected to dimming control. By reducing the output in the P 'form by dimming control of the P curve of the region above the reference luminance, it is possible to reduce the light output by DP'-Dp' ', thereby reducing the power consumption. Particularly, in this case, when the luminance is to be kept high, it is possible to reduce power consumption of the backlight unit by reducing the light output of the backlight unit without lowering the haptic brightness felt by the user for the bright screen by compensating the gain of the dimming control on the image data .

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, . ≪ / RTI > Accordingly, such modifications are deemed to be within the scope of the present invention, and the scope of the present invention should be determined by the following claims.

10: liquid crystal panel
20:
30: Dimming control section
40:
50: Gate driver
60: backlight driver
70: Backlight unit

Claims (13)

A liquid crystal panel for displaying an image;
A backlight unit for supplying light to the liquid crystal panel for displaying the image;
A driving circuit for controlling driving of the liquid crystal panel or the backlight unit for displaying the image and supplying a control signal including a video signal to the liquid crystal panel; And
And a dimming control unit controlling the driving circuit to perform dimming control including adjustment of an optical output of the backlight unit when the brightness of the image is equal to or greater than a predetermined reference brightness. The method according to claim 1,
The dimming control
Wherein the dimming control unit decreases the light output of the backlight unit continuously by a predetermined output reduction in accordance with a lapse of time or a change of a frame for display of the image. 3. The method of claim 2,
The dimming control unit
And performs the dimming control when the image based on the image signal is a dynamic image. 3. The method of claim 2,
The dimming control unit
And performs dimming control when the luminance difference between the previous frame and the current frame is equal to or smaller than a predetermined luminance difference value. 3. The method of claim 2,
The dimming control unit
Wherein the light output of the backlight unit is reduced within a luminance range equal to or higher than a predetermined lower luminance limit value. 3. The method of claim 2,
Wherein the dimming control increases a gain of the video signal in response to a decrease in light output of the backlight unit. A step of supplying a video signal for displaying an image from the outside;
Calculating a luminance of the image from the video signal by the dimming control unit;
The dimming control unit comparing the brightness of the image with a predetermined reference brightness;
A dimming control step in which the dimming control unit adjusts an optical output of the backlight unit when the brightness of the image is equal to or greater than the reference brightness; And
The liquid crystal panel and the driving unit displaying an image using the image signal by the dimming control; And a driving method of the liquid crystal display device. 8. The method of claim 7,
The dimming control step
Wherein the dimming control unit decreases the light output of the backlight unit by a predetermined output reduction amount in accordance with an elapse of time or a change of a frame for displaying the image. 8. The method of claim 7,
The step of supplying the control signal or the step of calculating the luminance of the image
And determining whether the image based on the image signal is a dynamic image,
Wherein the dimming control unit performs the dimming control when the image is a dynamic image. 8. The method of claim 7,
The dimming control step
Wherein the dimming control unit compares the luminance of the previous frame with the luminance of the current frame,
Wherein the dimming control step is performed when the luminance difference between the previous frame and the current frame is equal to or less than a predetermined luminance difference value. 11. The method according to claim 8 or 10,
The dimming control unit
Wherein the light output of the backlight unit is reduced within a luminance range that is equal to or higher than a predetermined lower luminance limit value. 9. The method of claim 8,
The dimming control step
Wherein the dimming control unit increases the gain of the video signal in response to a decrease in optical output of the backlight unit. 9. The method of claim 8,
The dimming control unit
And performs global dimming when the brightness is equal to or less than the reference brightness value.

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