KR20100077819A - Liquid crystal display device and method of driving the same - Google Patents

Abstract

PURPOSE: A liquid crystal display device and a driving method thereof are provided to improve display quality and power consumption by improving the gray scale of a data signal in a high-level mode and driving the device using a method which reduces the brightness of a backlight. CONSTITUTION: An input-on duty ratio output part(430) produces the input-on duty ratio of an input dimming signal. A data signal analysis part(420) calculates a gray scale distribution property value of an input data signal which is inputted according to a frame unit. A correlation analysis part(440) generates a first modulation coefficient and a default value according to the analysis. A data signal modulating part(450) outputs a data signal by modulating the gray scale of the input data signal when the first modulation coefficient is inputted. An on duty ratio modulating part(460) outputs a dimming signal by executing a modulation for the input-on duty ratio when the first modulation coefficient is inputted. A first selection switch(471) selects and outputs a data signal and an input data signal which are outputted from the data signal modulation part according to each on/off state of a high-level mode.

Description

Liquid crystal display device and method of driving the same

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a driving method thereof.

As the information society develops, the demand for display devices for displaying images is increasing in various forms. Recently, liquid crystal displays (LCDs), plasma display panels (PDPs), organic fields Various flat display devices such as organic light emitting diodes (OLEDs) are being utilized.

Among these flat panel display devices, liquid crystal display devices are widely used because they have advantages of miniaturization, light weight, thinness, and low power driving. On the other hand, an active matrix type liquid crystal display device in which a plurality of pixels are arranged in a matrix form and a switching transistor is formed in each of these pixels is currently widely used.

1 is a view schematically showing a general liquid crystal display device.

As illustrated, the liquid crystal display device 10 includes a driving circuit unit, a liquid crystal panel 20, and a backlight 70.

In the liquid crystal panel 20, a plurality of gate lines GL1 to GLn and a plurality of data lines DL1 to DLm cross each other to define a plurality of subpixels SP.

In each subpixel SP, a switching thin film transistor T connected to a gate line and a data line is formed. The switching thin film transistor T is connected to the pixel electrode. Meanwhile, a common electrode is formed corresponding to the pixel electrode, and an electric field is formed between the pixel electrode and the common electrode to drive the liquid crystal. The pixel electrode, the common electrode, and the liquid crystal positioned between these electrodes constitute a liquid crystal capacitor Clc. Meanwhile, a storage capacitor Cst is further configured in each pixel P, which stores a data voltage applied to the pixel electrode until the next frame. The subpixel SP includes R, G, and B subpixels SP that display red, green, and blue adjacent to each other.

The driving circuit section includes a control circuit section 30, a gate driving circuit section 40, a data driving circuit section 50, and an inverter circuit section 60.

The control circuit unit 30 samples the data control signal DCS for controlling the data driving circuit unit 50 and the data signal RGB in accordance with the data control signal DCS, and the data control signal DCS and the data signal ( RGB) is supplied to the data driver 350. In addition, the control circuit unit 30 supplies a gate control signal GCS for controlling the gate driving circuit unit 40 to the gate driving circuit unit 40.

The gate driving circuit unit 40 sequentially scans the plurality of gate wirings GL1 to GLn according to the gate control signal GCS to supply a turn-on voltage in the form of a pulse. According to the turn-on voltage, the switching transistor T is turned on.

On the other hand, the data driving circuit section 50 supplies the data signal RGB to the plurality of data wirings DL1 to DLm in response to the data control signal DCS supplied from the control circuit section 30. That is, the data voltage Vdata corresponding to the data signal RGB is generated, and the generated data voltage is output to the data wirings DL1 to DLm.

The inverter circuit unit 60 receives a dimming signal VBR and generates a backlight driving voltage (or driving current) in response to the dimming signal VBR.

The backlight 70 emits light and supplies the light to the display unit according to the backlight driving voltage supplied from the inverter circuit unit 60. The brightness of the backlight 70 is determined according to the on duty ratio of the dimming signal VBR.

On the other hand, recently, driving methods for improving the dynamic contrast ratio and reducing power consumption of an image by adjusting the brightness of the backlight 70 according to the gray level of the data signal RGB have been proposed. have. As one of such driving methods, a driving method of obtaining an average gray level of the data signal RGB and controlling the brightness of the backlight 70 by adjusting the dimming signal VBR according to the average brightness is used. In such a driving method, the backlight 70 is the maximum luminance in the brightest image, and as the image darkens, the luminance of the backlight is lowered.

However, when driving in such a driving method, when a part of the image displayed on the screen is brighter than most other parts, the brightness of the backlight 70 is adjusted based on the average gradation of the data signal RGB, Bright parts may also appear dark. In such a case, the visibility of the image is lowered, resulting in a problem that the image quality is lowered. In addition, when considering the image quality, there is a limit to lowering the luminance of the backlight 70 which occupies a large part of the power consumption of the liquid crystal display device. As described above, the conventional liquid crystal display device has a limitation in improving both image quality and power consumption.

The present invention has a problem to provide a liquid crystal display device and a driving method thereof capable of improving image quality and power consumption.

In order to achieve the above object, the present invention is a liquid crystal panel for displaying an image; A backlight for supplying light to the liquid crystal panel; An on duty ratio calculation unit for calculating an input on duty ratio of the input dimming signal; A data signal analysis unit for calculating a gray scale distribution characteristic value of the input data signal input in the frame unit; A first modulation coefficient and a default value are generated according to the correlation analysis between the input on duty ratio and the gray distribution characteristic value, and the second modulation is selected by selecting the first modulation coefficient / default value according to each of advanced mode on / off. A correlation analysis unit outputting as a coefficient; When the first modulation coefficient is input, the data signal is output by performing modulation on the gradation of the input data signal, and when the default value is input, the data signal outputting a data signal having the same gradation as the input data signal. A modulator; On-duty outputs a dimming signal by modulating the input on-duty ratio when the first modulation coefficient is input, and outputs a dimming signal corresponding to the input-on-duty ratio when the default value is input. A non-modulation unit; A first selection switch for selecting and outputting the data signal / the input data signal output from the data signal modulator according to each of the advanced mode on / off; A second selection switch for selecting and outputting a dimming signal / the input dimming signal output from the on-duty ratio modulator according to each of the advanced mode on / off; And an interleaver circuit for adjusting the brightness of the backlight according to the on-duty ratio of the dimming signal output from the second selection switch, wherein the first modulation coefficient of the current frame is the second modulation coefficient of previous n frames. And a gray level of the input data signal is modulated so as to increase the gray level of the input data signal when the input on duty ratio is modulated to decrease in response to the first modulation coefficient.

The correlation analyzer may include a correlation analysis block configured to output a first modulation coefficient according to a correlation analysis between the input on duty ratio and the gray scale distribution characteristic value; A default block for outputting the default value; And a third selection switch for selecting the first modulation coefficient / default value according to each of the on / off modes of the advanced mode and outputting the second modulation coefficient as the second modulation coefficient.

When the first modulation coefficient is input, the data signal modulator outputs a data signal by modulating the gray level of the input data signal, and when the default value is input, the data having the same gray level as the input data signal. A data signal modulation block for outputting a signal; And a fourth selection switch for selecting and outputting the data signal / the input data signal output from the data signal modulation block according to each of the advanced mode on / off.

When the first modulation coefficient is input, the on-duty ratio modulator performs modulation on the input on-duty ratio, and outputs the modulated signal. An output duty ratio modulation block; And a fifth selection switch configured to select and output the on duty ratio / the input on duty ratio output from the on duty ratio modulation block according to each of the advanced mode on / off.

The gradation distribution characteristic value includes a target gradation, and as the target gradation decreases, the amount by which the input on duty ratio decreases in response to the first modulation coefficient increases, and the target gradation is the gradation of the input data signal. It may be the maximum gray scale of the gray scale distribution except the upper x% in the distribution.

In another aspect, the present invention includes the steps of calculating an input on duty ratio of the input dimming signal; Calculating a gray scale distribution characteristic value of the input data signal input in units of frames; A first modulation coefficient and a default value are generated according to the correlation analysis between the input on duty ratio and the gray distribution characteristic value, and the second modulation is selected by selecting the first modulation coefficient / default value according to each of advanced mode on / off. Outputting as a coefficient; In the data signal modulator, when the first modulation coefficient is input, the data signal is output by performing modulation on the gray level of the input data signal, and when the default value is input, data having the same gray level as the input data signal. Outputting a signal; In the on-duty ratio modulator, when the first modulation coefficient is input, modulate the input on-duty ratio to output a dimming signal, and when the default value is input, dimming corresponding to the input on-duty ratio. Outputting a signal; Selecting and outputting the data signal / the input data signal output from the data signal modulator according to each of the advanced mode on / off; Selecting and outputting a dimming signal / the input dimming signal output from the on duty ratio modulator according to each of the advanced mode on / off; Adjusting the brightness of the backlight according to the on duty ratio of the selected and output dimming signal; And displaying an image on a liquid crystal panel by receiving light from the backlight, wherein the first modulation coefficient of the current frame is generated by reflecting the second modulation coefficient of the previous n frames, and the first modulation coefficient. When the input on duty ratio is modulated so as to decrease in response, the gray level of the input data signal is modulated so as to increase.

The data signal modulator may further include selecting and outputting the input data signal when the advanced mode is turned off.

The on duty ratio modulator may further include selecting the input on duty ratio and outputting a dimming signal corresponding to the input on duty ratio when the advanced mode is turned off.

The gradation distribution characteristic value includes a target gradation, and as the target gradation decreases, the amount by which the input on duty ratio decreases in response to the first modulation coefficient increases, and the target gradation is the gradation of the input data signal. It may be the maximum gray scale of the gray scale distribution except the upper x% in the distribution. The x% may be 50% or less.

The liquid crystal display device according to the present invention can select a normal mode and an advanced mode. Furthermore, in the advanced mode, the image signal and power consumption can be improved by driving the method of increasing the gray level of the data signal and lowering the brightness of the backlight.

In addition, since the grayscale modulation of the data signal and the on-duty ratio modulation of the input dimming signal are not performed during the period in which the advanced mode is initially off after the power-on time, the brightness of the backlight is sharply changed when the advanced mode is changed from off to on. The image quality can be improved by preventing the change.

Also, during the period in which the advanced mode is initially off after the power-on time, the on-duty ratio of the input data signal and the input dimming signal bypasses the data modulator and the on-duty ratio modulator so that the input data signal and the on-duty ratio In terms of outputting the original signal without signal manipulation, more stable driving can be obtained.

Hereinafter, with reference to the drawings will be described embodiments of the present invention.

2 is a view schematically showing a liquid crystal display device according to a first embodiment of the present invention, and FIG. 3 is a view showing an image quality processor of FIG. 2.

As illustrated, the liquid crystal display device 100 according to the exemplary embodiment of the present invention includes a driving circuit unit, a liquid crystal panel 200, and a backlight 700.

In the liquid crystal panel 200, a plurality of gate lines GL1 to GLn and a plurality of data lines DL1 to DLm cross each other to define a plurality of subpixels SP.

In each subpixel SP, a switching thin film transistor T connected to gate wirings and data wirings GL1 to GLn and DL1 to DLm is formed. The switching thin film transistor T is connected to the pixel electrode. Meanwhile, a common electrode is formed corresponding to the pixel electrode, and an electric field is formed between the pixel electrode and the common electrode to drive the liquid crystal. The pixel electrode, the common electrode, and the liquid crystal positioned between these electrodes constitute a liquid crystal capacitor Clc. On the other hand, each subpixel SP further includes a storage capacitor Cst, which stores a data voltage applied to the pixel electrode until the next frame.

The subpixel SP may include red, green, and blue R, G, and B subpixels. The neighboring R, G, and B subpixels SP constitute pixels that are video display units.

The driving circuit unit may include a system circuit unit 300, a control circuit unit 400, an inverter circuit unit 500, a power generator 610, a gate driver circuit unit 620, a data driver circuit unit 630, and a gamma reference voltage generator 640. ).

The control circuit 400 is an input data signal RGB_IN, a vertical synchronization signal Vsync, a horizontal synchronization signal Vsync, a clock signal DCLK, and data from a system circuit 300 such as a TV system or a video card. The control signal TCS such as the Able DE is received. Although not shown, such signals may be input through an interface configured in the control circuit unit 400. Each input data signal RGB_IN includes an R data signal, a G data signal, and a B data signal, and these R, G, and B data signals correspond to the R, G, and B subpixels SP, respectively.

The control circuit 400 generates a gate control signal GCS for controlling the gate driving circuit 620 and a data control signal DCS for controlling the data driving circuit 630 using the input control signal. . The gate control signal GCS includes a gate start pulse (GSP), a gate shift clock (GSC), a gate output enable signal (GOE), and the like. The data control signal (DCS) includes a source start pulse (SSP), a source shift clock (SSC), a source output enable signal (SOE), and a polarity signal (POL). It includes. For example, the above operation may be performed by the timing controller 490 of the control circuit 400.

Also, the image quality processing unit 410 of the control circuit unit 400 receives the input data signal RGB_IN and the input dimming signal VBR_IN from the system circuit unit 300, and inputs the input data signal RGB_IN and the input dimming signal ( VBR_IN) modulates the input on duty ratio.

On the other hand, the control circuit unit 400 outputs or outputs the first output dimming signals RGB_C and VBR_OUT1 corresponding to the modulated modulation data signal and the modulation on duty ratio according to the selection of the operation mode. It is determined whether to output the data signal and the input dimming signals RGB_IN and VBR_IN. For example, the driving mode may include an advanced mode and a normal mode. When the advanced mode is selected, the image quality processing unit 410 outputs the modulated modulation data signal and the first output dimming signals RGB_C and VBR_OUT1 corresponding to the modulation on duty ratio. When the normal mode is selected, the image quality processing unit 410 outputs input data signals and input dimming signals RGB_IN and VBR_IN.

In the embodiment of the present invention, the advanced mode is a driving mode for improving image quality and power consumption, and may be selected by the user or the system circuit unit 300 itself. For example, the advanced mode according to the embodiment of the present invention is also called an OPC (Optimal Power Control) mode, and may be referred to as a mode driven to optimize both of image quality and power consumption aspects. This will be described in more detail later.

The output data signal RGB_OUT output from the video quality processor 410 is input to the timing controller 490 and supplied to the data driver circuit 630 together with the data control signal DCS in accordance with the synchronization signal.

In addition, the second output dimming signal VBR_OUT2 output from the image quality processing unit 410 is supplied to the inverter circuit unit 500 according to the synchronization signal.

On the other hand, the dimming signal will be described in more detail. The image quality processor 410 modulates the on-duty ratio of the input dimming signal VBR_IN to generate a first output dimming signal VBR_OUT1 corresponding to the modulated on-duty ratio. The on-duty ratio determines the emission time of the backlight 700, and ultimately, determines the luminance of the backlight 700. As the on-duty ratio increases, the luminance increases, and the decrease decreases the luminance. For example, the on-duty ratio determines the light emission time of the backlight 700. As the on-duty ratio increases, the light emission time becomes longer, and as the on-duty ratio decreases, the light emission time becomes shorter. As such, the on-duty ratio can adjust the luminance of the backlight 700 by adjusting the light emission time of the backlight 700.

The input dimming signal VBR_IN may be supplied in an analog voltage method or a pulse width modulation (PWM) method, and thus the method of the first output dimming signal VBR_OUT1 corresponding to the modulation on duty ratio may be determined. have. For an analog voltage dimming signal, the on-duty ratio is determined according to the voltage level. For example, the higher the voltage level, the higher the on-duty ratio, and the lower the voltage level, the lower the on-duty ratio. For the PWM dimming signal, the on-duty ratio is determined according to the pulse width. For example, the wider pulse width increases the on-duty ratio, and the narrower pulse width decreases the on-duty ratio. On the other hand, in the embodiment of the present invention, description will be given mainly on the dimming signal of the PWM method.

The input dimming signal VBR_IN may be selected and adjusted by the user or the system circuit unit 300 itself. For example, the user may adjust the input dimming signal VBR_IN by using a control means such as a remote controller, a mouse, a button, and the like. In addition, the input dimming signal VBR_IN may be adjusted through a sensor for measuring illuminance of the external environment. Also, the input dimming signal VBR_IN may be adjusted in the system circuit unit 300 for the purpose of image quality control or power control.

The input dimming signal VBR_IN may be transmitted to the control circuit unit 410 through the inverter circuit unit 500.

The gamma reference voltage generator 640 generates a gamma reference voltage Vgamma by dividing the high potential voltage and the low potential voltage generated from the power generator 610 and supplies it to the data driving circuit unit 630.

The power generation unit 610 receives the power supply voltage VCC from the system circuit unit 300, and generates and supplies a driving voltage for driving the components of the driving circuit unit.

The gate driving circuit unit 620 sequentially scans the plurality of gate wirings GL1 to GLn in response to the gate control signal GCS supplied from the control circuit unit 400. During each scan period, a turn-on voltage in the form of a pulse is supplied to the gate wirings GL1 to GLn. On the other hand, the turn-off voltage is continuously supplied to the gate lines GL1 to GLn until the scan period of the next frame. As the turn-on voltage is applied during the scan period, the switching thin film transistor T is turned on.

The data driving circuit unit 630 supplies the output data signal RGB_OUT to the plurality of data wirings DL1 to DLm in response to the data control signal DCS supplied from the control circuit unit 400. That is, the data voltage corresponding to the output data signal RGB_OUT is generated using the gamma reference voltage Vgamma, and the generated data voltage is output to the data wirings DL1 to DLm.

The inverter circuit unit 500 generates the driving voltage (or driving current) of the backlight 700 by using the second output dimming signal VBR_OUT2 received from the control circuit unit 400. For example, the inverter circuit unit 500 receives the DC voltage VINV from the system circuit unit 300 and converts the DC voltage into an AC voltage which is a driving voltage. The waveform of the AC voltage is the second output dimming signal VBR_OUT2. It is determined by on duty ratio. For example, the supply time of the driving voltage is determined in proportion to the on duty ratio of the second output dimming signal VBR_OUT2.

The driving voltage generated as described above is supplied to the backlight 700 to adjust the brightness of light emitted from the backlight 700. That is, since the light emission time of the backlight 700 is adjusted according to the supply time of the driving voltage, the brightness of the backlight 700 is eventually adjusted according to the on-duty ratio.

Meanwhile, when the second output dimming signal VBR_OUT2 is an analog dimming signal, the second output dimming signal VBR_OUT2 is a PWM method through a dimming signal conversion circuit (not shown) in the inverter circuit unit 500. It can be converted into a dimming signal of. The inverter circuit unit 500 may generate a driving voltage by using the PWM dimming signal converted as described above.

The backlight 700 emits light by receiving a driving voltage supplied from the inverter circuit unit 500. As the backlight 700, a Cold Cathode Fluorescent Lamp (CCFL), an External Electrode Fluorescent Lamp (EEFL), a Light Emitting Diode (LED), or the like may be used.

Hereinafter, the image quality processing unit 410 will be described in more detail.

The image quality processing unit 410 may perform data signal modulation and on-duty ratio modulation for driving the advanced mode described above. When driving the advanced mode of the liquid crystal display device 100 according to the embodiment of the present invention, it is possible to make a significant improvement in terms of image quality and power consumption as compared with driving the conventional liquid crystal display device.

In this regard, it will be described with reference to FIG. 4 further. FIG. 4 shows the gradation of the data signal and the brightness of the backlight when driving a general liquid crystal display and driving a high-end mode of a liquid crystal display according to an embodiment of the present invention.

The final image that is finally displayed through the liquid crystal display and viewed by the user is an image in which the luminance of the backlight is combined with the data image generated in the liquid crystal panel depending on the input data signal. In other words, the data image is an image generated in the liquid crystal panel by the data signal output from the system circuit unit.

In a general liquid crystal display device, a luminance of 100% of the on-duty ratio of a dimming signal, that is, a backlight of 100% is supplied to the liquid crystal panel, and the input data signal is supplied to the liquid crystal panel without being modulated. As described above, in the general liquid crystal display device, the backlight is driven at 100%. However, the backlight is a component that consumes significantly higher power than other components. Thus, the liquid crystal display device consumes considerable power consumption. In addition, since the luminance of the backlight is fixed and the dynamic contrast ratio and the color gamut of the final image have a limit determined depending on the input data image, the dynamic contrast ratio and The range of color reproduction has a limitation in the display of a moving image which is an important image quality factor.

On the other hand, for the liquid crystal display device 100 according to the embodiment of the present invention, it is possible to significantly improve both power consumption and image quality when driving in the advanced mode. Referring to FIG. 4, for example, with respect to a general liquid crystal display device and a liquid crystal display device 100 driven in an advanced mode according to an embodiment of the present invention, the input data signal RGB_IN having the same gray level and the on-duty ratio An input dimming signal VBR_IN of 100% is input and it is assumed that the final image has the same brightness. In this case, when the advanced mode is selected in the liquid crystal display according to the exemplary embodiment of the present invention, the grayscale of the input data signal RGB_IN and the on-duty ratio of the input dimming signal VBR_IN are modulated. The modulation is performed in consideration of the correlation between the gray scale and the on-duty ratio of the input dimming signal VBR_IN. For example, the input data signal RGB_IN is modulated to generate a modulation data signal RGB_C having a gray level higher than that of the input data signal RGB_IN, and modulated so that the on-duty ratio is less than 100%. That is, in the advanced mode, the final image having the same brightness as that of the general liquid crystal display device can be displayed by increasing the gray level and decreasing the brightness of the backlight. Accordingly, the power consumption of the backlight can be considerably lowered.

Furthermore, in the advanced mode according to the embodiment of the present invention, since the on-duty ratio is modulated to decrease the brightness of the backlight as the gray level of the input data signal is lowered, the dynamic contrast ratio is eventually improved.

Further, in the advanced mode according to the embodiment of the present invention, the brightness of the backlight is lowered as compared with the general liquid crystal display device. Therefore, the degree of light leakage of the backlight passing through the liquid crystal panel 200 is reduced, so that the color gamut can be improved.

As such, when driving the liquid crystal display device in the advanced mode according to the embodiment of the present invention, all aspects of image quality and power consumption can be considerably improved compared with the related art.

As described above, the image quality processing unit 410 that can operate the LCD in the advanced mode and can also operate in the general mode will be described in more detail.

The image processing quality unit 410 may include a data signal analyzer 420, an on duty ratio calculator 430, a correlation analyzer 440, a data signal modulator 450, an on duty ratio modulator 460, First and second selector switches 471 and 472.

The data signal analyzer 420 analyzes the attributes of the input data signal RGB_IN. For example, the data signal analyzer 420 extracts a gray level among the attributes of the input data signal RGB_IN input in units of frames, and shows a histogram indicating a distribution thereof. It can be analyzed by calculating

The analysis result is transmitted to the correlation analysis unit 440. As an analysis result, the gray scale distribution characteristic value representing the gray scale distribution characteristic may be transmitted to the correlation analyzer 440. For example, the gray scale distribution characteristic value may include at least one of an average gray scale, a maximum gray scale, a minimum gray scale, a target gray scale, and a value calculated therefrom. In relation to the target gradation, for example, the maximum gradation of the gradation distribution except for the upper x% may correspond to the target gradation. On the other hand, the top x% may vary from the manufacturer side, for example, may be 50% or less. More preferably, x% may be approximately 10% or approximately 100 * (1/8)%.

The on duty ratio calculation unit 430 calculates and calculates an input on duty ratio of the input dimming signal VBR_IN supplied from the system circuit unit 300. The calculated input on duty ratio is transmitted to the correlation analyzer 440.

The correlation analysis unit 440 analyzes the correlation between the gray scale distribution characteristic and the input on duty ratio, as an analysis result of the input data signal RGB_IN. That is, the correlation analyzer 430 analyzes the image displayed by combining the luminance of the backlight 700 by the input data signal RGB_IN and the input dimming signal VBR_IN. Based on the analysis result, in order to display an optimized image in terms of image quality and power consumption, a degree of modulation of the gray level of the input data signal RGB_IN and a degree of input on duty ratio are determined. .

For example, the correlation analyzer 440 may determine that the on-duty ratio is lowered and the gray level is increased. The reduction degree of the input on duty ratio may be determined according to the gray scale distribution characteristic value. For example, the amount of reduction in the on-duty ratio may be determined according to the gray scale distribution characteristic value. In other words, as the gray scale distribution characteristic value is lowered, the amount of reduction in the on-duty ratio may increase. More preferably, it may be determined according to the target gradation. For example, as the target gradation is lowered, the amount of reduction in the on-duty ratio may increase. On the other hand, the gray level of the input data signal RGB_IN can be increased in inverse proportion to the amount of decrease in the on-duty ratio.

As such, the correlation analysis unit 440 analyzes the correlation between the gray distribution characteristics and the on-duty ratio to determine the degree of data signal modulation and on-duty ratio modulation. The analysis result is, for example, a modulation coefficient. output as (k). That is, the modulation coefficient k is determined by using the gradation distribution characteristics and the on-duty ratios as correlation variables.

The data signal modulator 450 modulates the input data signal RGB_IN in response to the modulation coefficient k. In addition, the on duty ratio modulator 460 modulates the input on duty ratio in response to the modulation coefficient k, and outputs a first output dimming signal VBR_OUT1 corresponding to the modulation on duty ratio.

For example, the data signal modulator 450 can increase the gradation of the input data signal RGB_IN in proportion to the modulation coefficient k, and the on-duty ratio modulator 460 is inversely proportional to the modulation coefficient k. The input on duty ratio can be lowered.

Meanwhile, in calculating the modulation coefficient k of the current frame, not only the input data signal RGB_IN and the input on duty ratio of the current frame, but also the modulation coefficient of the previous n frames may be reflected. That is, it refers to the correlation analysis result of the previous n frames. This will be described taking modulation of the on-duty ratio as an example.

For example, when a black data signal is input from the current frame and the input on duty ratio is 100%, the correlation analyzer 440 may based only on the correlation between the input data signal RGB_IN and the input on duty ratio. It is assumed that the modulation coefficient k is output to amplify the data signal and reduce the on-duty ratio to, for example, 30%. At this time, if the on-duty ratio of the output dimming signal is maintained at 100% for the previous n frames, the brightness of the backlight 700 is drastically reduced from 100% to 30% in the current frame. Such a sudden change in the brightness of the backlight 700 may cause deterioration of image quality.

Therefore, the brightness of the backlight 700 is sequentially decreased, for example, 100%-> 98%-> 96%-> ...-> 30%, so as to prevent a sudden change in the brightness of the backlight 700. Will be required. Accordingly, in calculating the modulation coefficient k, the modulation coefficients of the previous n frames are reflected. For example, each of the modulation coefficients of the previous n frames is weighted, and the preliminary modulation coefficients depending on the input data signal and the input on duty ratio of the current frame are weighted, and the averages of the modulation coefficients are obtained. The modulation coefficient of the frame can be obtained. E.g,

kn + 1 = f ((a1 * k1 + a2 * k2 + ... + an * kn + bkp) / n)

It can be expressed as a function of the mean value. Where k1 to kn are modulation coefficients for each previous n frames, kn + 1 is a modulation coefficient for the current frame, a1 to an are weights for each modulation coefficient of the previous n frames, and kp is a current frame Is a preliminary modulation coefficient depending on the grayscale and the input on duty ratio of the input data signal RGB_IN, and b is a weight for the preliminary modulation coefficient. Here, a1 to an and b may be greater than zero. And, a1 to an and b become 1, and an arithmetic mean value can be used as a function argument.

On the other hand, in response to the modulation coefficient k, the signal modulation in the on-duty modulator 460 and the data signal modulator 450 is, for example,

ORD_OUT = f (ORD_IN / k),

GRL_C = f (GRL_IN * k)

It can be expressed as a function such as Here, ORD_IN and ORD_OUT are input on duty ratio and modulation on duty ratio, respectively, and GRL_IN and GRL_C correspond to the grayscale of the input data signal and the modulated grayscale, respectively.

The first selection switch 471 receives an input data signal RGB_IN and a modulation data signal RGB_C from an input terminal, and receives an advanced mode enable signal OPC_EN from a switching terminal. When the advanced mode enable signal OPC_EN is enabled (or a logic signal "1", or high), that is, when the advanced mode is selected (ON), the modulation data signal (RGB_C) is It is output through the output terminal. On the other hand, when the advanced mode enable signal OPC_EN is in the disabled state (logical signal "0", or low), that is, when the advanced mode is not selected and turned off (OFF), the input data signal RGB_IN is output. Is output via

The second selection switch 472 receives an input dimming signal VBR_IN and a first output dimming signal VBR_OUT1 from an input terminal, and receives an advanced mode enable signal OPC_EN from a switching terminal. When the advanced mode enable signal OPC_EN is in the enable state, the first output dimming signal VBR_OUT1 is output through the output terminal. On the other hand, when the advanced mode enable signal OPC_EN is in the disabled state, the input dimming signal VBR_IN is output through the output terminal.

That is, when the advanced mode for driving the improvement of image quality and power consumption is selected, the advanced mode enable signal OPC_EN has an enabled state, and the modulated data signal and the modulated on through the image quality processor 410 are enabled. The dimming signals RGB_C and VBR_OUT1 corresponding to the duty ratio are output. If the image quality improvement and the power consumption improvement are not required, for example, when the normal mode is selected, the advanced mode enable signal OPC_EN is in a disabled state and is modulated by the image quality processor 410. The dimming signals RGB_C and VBR_OUT1 corresponding to the data signal and the modulated on-duty ratio are not output, but the input data signal and the input dimming signals RGB_IN and VBR_IN input from the system circuit unit 300 are output.

Meanwhile, in using the liquid crystal display device 100 according to the first embodiment described above, a problem may occur at the time of power-on of the liquid crystal display device 100. For example, depending on the initial driving characteristics of the backlight 700 itself, the brightness of the backlight 700 is preferably 100% at the time of power-on. Otherwise, while the liquid crystal display 100 is being driven, the backlight 700 may not generate the desired luminance. For example, when white is displayed, the image may be displayed dark.

It is assumed that the advanced mode operates from a power-on time and a black data signal is input at the power-on time. In the advanced mode, the main purpose is to reduce the power consumption by lowering the brightness of the backlight 700. Therefore, when the black data signal is input and the input on-duty ratio is 100%, the image processing unit 410 is 100%. By modulating the input on duty ratio, for example, a modulation on duty ratio of 30% is generated. In such a case, the backlight 700 has only 30% of the brightness at the time of power-on, resulting in failure to meet the initial driving characteristics of the backlight 700 itself, which should have 100% of the brightness at the time of power-on. do. In addition, the power sequence is different for each of the secondary companies that use the liquid crystal display device 100 to produce a product such as a TV. Therefore, it is difficult to unilaterally adjust the brightness of the backlight 700 in the control circuit unit 400.

Accordingly, a method of disabling the advanced mode enable signal for a predetermined time after power-on and using the advanced mode enable signal in an enabled state in accordance with the power sequence of the secondary company has been proposed. On the other hand, after power-on, for example, a black data signal is input as the input data signal RGB_IN for 1 to 2 seconds. However, regardless of whether the advanced mode is on or off, the image quality processing unit 410 internally performs data modulation and on-duty modulation for performing the advanced mode. Therefore, when the black data signal RGB_IN is initially input, for example, a modulation on duty ratio of 30% is generated. Of course, since the advanced mode off state is maintained for an initial predetermined time after the power-on time, the on-duty ratio of the dimming signal output from the image quality processing unit 410 becomes 100% of the input-on-duty ratio, so that the backlight 700 mentioned above ) Its initial driving characteristics are satisfied.

However, after a certain time, when the advanced mode is turned on, the brightness of the backlight 700 rapidly changes. This will be described with reference to FIG. 5 further.

5 is a diagram illustrating a change in a dimming signal when the advanced mode enable signal is changed from the disabled state to the enabled state after the power-on time in the liquid crystal display according to the first embodiment of the present invention. In FIG. 5, the dimming signal of the PWM method is taken as an example, and the input dimming signal VBR_IN has a continuously high state, and the input on-duty ratio of the input dimming signal VBR_IN is 100%.

Referring to FIG. 5, when the advanced mode enable signal is disabled, the on-duty ratio modulator 460 continuously generates the first output dimming signal VBR_OUT1 having a modulation-on-duty ratio of 30%. The on-duty ratio of the second output dimming signal VBR_OUT1 output through the second switch 472 is an input-on-duty ratio of 100%.

However, when the advanced mode enable signal is changed to the enabled state, the second switch 472 is the first output dimming signal VBR_OUT1 corresponding to the 30% modulation on duty ratio generated by the on-duty modulator 460. ) Will be printed. As a result, when the advanced mode enable signal is changed to the enabled state, the brightness of the backlight 700 may change rapidly from 100% to 30%, thereby degrading the image quality.

In addition, when the advanced mode is in the on state, the brightness of the backlight 700 is lowered, and thus the degree of light leakage passing through the liquid crystal panel 200 is reduced as compared with the off state. Therefore, the black image displayed when the advanced mode is on appears somewhat darker than the black image displayed when the advanced mode is off. Thus, when the advanced mode changes from off to on, the viewer can feel that flicker occurs.

As described above, in the liquid crystal display device 100 according to the first embodiment, the image quality may be degraded during the initial stage after the power-on. This problem can be solved through the following embodiments.

FIG. 6 is a diagram illustrating an image quality processor of a liquid crystal display according to a second exemplary embodiment of the present invention, and FIG. 7 is a diagram illustrating a correlation analyzer, a data signal modulator, and an on-duty ratio modulator of FIG. 6. . In the second embodiment, for convenience of description, the image quality processing unit of the liquid crystal display is mainly shown, and the remaining components are omitted. Components omitted in the second embodiment are similar to those in the first embodiment, and thus descriptions thereof may be omitted.

6 and 7, the correlation analyzer 440 of the image quality processor 410 includes a correlation analysis block 441, a default block 442, and a third selection switch 443. do.

The correlation analysis block 441 can have the same function as the correlation analysis unit 440 of FIG. 3 in the first embodiment. For example, the correlation analysis block 441 analyzes the correlation between the result of analyzing the input data signal RGB_IN, for example, the gray scale distribution characteristic and the input on duty ratio. Such an analysis result is output as a 1st modulation coefficient k_1, for example. The first modulation coefficient k_1 corresponds to the modulation coefficient (k in FIG. 3) in the first embodiment. That is, the first modulation coefficient k_1 is calculated based on the tone distribution characteristic and the on duty ratio, which are the objects of correlation. Also, similarly to the first embodiment, the first modulation coefficient k_1 is calculated by reflecting the second modulation coefficient k_2 output during the previous n frames from the correlation analyzer 440.

The default block 442 outputs a default value k_d. The default value may be called a reset value. That is, the default value is a signal that resets the data signal modulator 450 and the on-duty ratio modulator 460 to default the modulation of the gradation and on-duty ratio of the data signal, that is, to not modulate. to be.

The third selection switch 443 receives the first modulation coefficient k_1 and the default value k_d from the input terminal, and receives the advanced mode enable signal OPC_EN from the switching terminal. When the advanced mode enable signal OPC_EN is in the enabled state, the first modulation coefficient k_1 is output through the output terminal. On the other hand, when the advanced mode enable signal OPC_EN is in the disabled state, the default value k_d is output through the output terminal. That is, the third selector switch 443 is the second modulation coefficient k_1, and according to the state of the advanced mode enable signal OPC_EN, one of the first modulation coefficient k_1 and the default value k_d is selected. Will be chosen.

When the advanced mode enable signal OPC_EN is disabled, that is, the advanced mode is off, the data signal modulator 450 and the on-duty ratio modulator 460 set the default value k_d to the second modulation coefficient k_2. Will be input. Accordingly, the data signal modulator 450 may output the input data signal RGB_IN without modulating the data signal. The on duty ratio modulator 460 outputs the first output dimming signal VBR_OUT1 corresponding to the input on duty ratio without modulating the on duty ratio. For example, with respect to the default value k_d, the data signal modulator 450 and the on-duty ratio modulator 460 perform calculations for modulation, but the gray level of the input data signal RGB_IN as a result of the calculation. And the on-duty ratio of the input dimming signal VBR_IN may be calculated.

Meanwhile, when the advanced mode enable signal OPC_EN is enabled, that is, the advanced mode is on, the data signal modulator 450 and the on-duty ratio modulator 460 set the first modulation coefficient k_1 to the second state. It is inputted as the modulation coefficient (k_2). Accordingly, the data signal modulator 450 outputs the modulated data signal RGB_C by performing data signal modulation according to the first modulation coefficient k_1. The on duty ratio modulator 460 performs on duty modulation according to the first modulation coefficient k_1 to generate a modulation on duty ratio and output a first output dimming signal VBR_OUT1 corresponding thereto.

As described above, when the advanced mode is off, the input data signal and on-duty ratio are maintained by selecting the default value k_d as the second modulation coefficient k_2. When the advanced mode is on, data modulation and on-duty ratio modulation are performed by selecting the first modulation coefficient k_1 as the second modulation coefficient k_2. Accordingly, it is possible to improve the deterioration of the image quality when the advanced mode is changed from the off state to the on state after the power-on time, which will be described in more detail.

When the black input data signal RGB_IN is input after the power-on time and before the advanced mode is turned on, and the input dimming signal VBR_IN having an on duty ratio of 100% is input, the correlation analyzer 440 determines the default value ( k_d) is selected to be finally output as the second modulation coefficient k_2. Accordingly, the input on duty ratio is maintained, and the first output dimming signal VBR_OUT1 corresponding to the input on duty ratio of 100% is output through the on duty ratio modulator 460. Of course, since the advanced mode is off, the second selection switch 472 outputs the input dimming signal VBR_IN.

After that, when the advanced mode is turned on while the black input data signal RGB_IN and the input dimming signal VBR_IN having an on duty ratio of 100% are continuously input, the correlation analyzer 440 performs a first modulation. The coefficient k_1 is selected and finally output as the second modulation coefficient k_2.

In this regard, as described above, the correlation analysis block 441 also reflects the second modulation coefficient k_2 of the previous n frames in calculating the first modulation coefficient k_1. That is, it refers to the correlation analysis result of the previous n frames.

Here, for the n frames before the advanced mode is turned on, the default value k_d was output as the second modulation coefficient k_2, and accordingly, the on-duty ratio of the first output dimming signal VBR_OUT1 is input on. Duty ratio 100% was output.

Therefore, for the current frame in which the advanced mode is turned on, the second modulation coefficients k_2 of the n frames before the advanced mode is turned on, that is, the default values k_d, calculate the first modulation coefficient k_1 of the current frame. The default value k_d is reflected to calculate the first modulation coefficient k_1 of the frame up to (n-1) frames after the current frame.

In this regard, in the first embodiment, the correlation analyzer 440 of FIG. 3 reflects the modulation coefficients of the previous n frames in calculating the modulation coefficients of the current frame, so that the on-duty ratio is 100, for example. It is mentioned that it does not decrease rapidly from 30% to 30%, but gradually decreases from 100%-> 98%-> 96%-> ...-> 30%. Meanwhile, also in the second embodiment, the on-duty ratio modulator 260 maintains the input on-duty ratio of 100% after the power-on time until the advanced mode is turned on, so that the first output dimming signal VBR_OUT1 has a 100% on-duty ratio. ) Will be created. Therefore, even if the advanced mode is turned on after the power-on time, the second duty cycle k_2 of the previous n frames is reflected on the frames after the advanced mode on, so that the on-duty ratio is, for example, FIG. 7. As shown in the figure, gradually decrease from 100%-> 98%-> 96%-> ...-> 30%.

Of course, after the advanced mode is turned on after the power-on time, the modulation of the input data signal may be gradually increased in accordance with the change of the second modulation coefficient k_2 as opposed to the decrease in the on-tuty ratio as described above.

Accordingly, when the advanced mode is initially changed from off to on after the power-on time, the brightness of the backlight 700 may be changed rapidly, thereby reducing the image quality.

FIG. 8 is a diagram illustrating an image quality processor of a liquid crystal display according to a third exemplary embodiment of the present invention, and FIG. 9 is a diagram illustrating a correlation analyzer, a data signal modulator, and an on-duty ratio modulator of FIG. 8. . In the third embodiment, for convenience of description, the image quality processing unit of the liquid crystal display device is illustrated, and the remaining components are omitted. Components omitted in the third embodiment are similar to those in the first and second embodiments, and thus descriptions thereof may be omitted.

8 and 9, the data signal modulator 450 of the image quality processor 410 includes a data signal modulator block 451 and a fourth selection switch 452. The on duty ratio modulation unit 460 includes an on duty ratio modulation block 461 and a fifth selection switch 462.

Here, the data signal modulation block 451 can function the same as the data signal modulation section 450 in FIGS. 3 and 7 in the first and second embodiments. That is, the input data signal RGB_IN is modulated according to the second modulation coefficient k_2.

The on-duty non-modulation block 461 can function similar to the on-duty non-modulation section 460 of FIGS. 3 and 7 in the first and second embodiments. That is, the input on duty ratio is modulated according to the second modulation coefficient k_2.

Meanwhile, the data signal modulator 450 includes a fourth selection switch 452 and according to the advanced mode enable signal OPC_EN input through the switching stage, the input data signal RGB_IN input through the input terminal. And one of the modulated data signal RGB_C is outputted. For example, when the enable signal OPC_EN in the advanced mode is in the disabled state, the input data signal RGB_IN is output, and in the enabled state, the modulated data signal RGB_C is output.

In addition, the on-duty ratio modulator 460 includes a fifth selection switch 462 and according to the advanced mode enable signal OPC_EN input through the switching stage, the on-duty ratio calculator 460 input through the input terminal ( One of the input on duty ratio and the modulation on duty ratio transmitted from 430 is selected and output. For example, the input on duty ratio is output when the enable signal OPC_EN in the advanced mode is disabled, and the modulation on duty ratio is output when the enable signal OPC_EN is in the disabled state. Meanwhile, the on duty ratio modulator 460 outputs the first output dimming signal VBR_OUT1 corresponding to the selected on duty ratio.

As described above, the third embodiment compares the data signal modulation block and the on-duty non-modulation blocks 451 and 461 when the advanced mode enable signal OPC_EN is in the disabled state as compared with the second embodiment. The input data signal RGB_IN and the input on duty ratio are selected for the switching operation without selecting the output signal. Referring to the second embodiment, of course, when the advanced mode enable signal OPC_EN is in the disabled state, a default value is output so that the data signal modulator and the on-duty ratio modulator (450, 460 in Fig. 7) result. This generates the same signal as the input data signal and the input on duty ratio. However, the data signal modulator and the on duty ratio modulator of the second embodiment do not bypass the input data signal and the input on duty ratio, and generate the same signal as the input data signal and the input on duty ratio through calculation. On the other hand, in the third embodiment of the present invention, when the advanced mode enable signal OPC_EN is in the disabled state, the operation of bypassing the input data signal RGB_IN and the input on duty ratio is performed by the switching operation. Done. As described above, in the third embodiment, when the advanced mode enable signal OPC_EN is in the disabled state, more stable driving can be ensured in terms of outputting the original signal without signal manipulation.

Embodiment of the present invention described above is an example of the present invention, it is possible to change freely within the scope included in the spirit of the present invention. Accordingly, the invention includes modifications of the invention within the scope of the appended claims and their equivalents.

1 is a view schematically showing a general liquid crystal display device.

2 is a schematic view of a liquid crystal display device according to a first embodiment of the present invention;

3 is a view illustrating an image quality processing unit of FIG. 2.

4 is a diagram showing gradation of a data signal and luminance of a backlight when driving a general liquid crystal display and driving an advanced mode of a liquid crystal display according to an embodiment of the present invention.

FIG. 5 is a view illustrating a change in a dimming signal when an advanced mode enable signal is changed from a disabled state to an enabled state after a power-on time in the liquid crystal display according to the first embodiment of the present invention.

6 is a view showing an image quality processing unit of the liquid crystal display according to the second embodiment of the present invention.

FIG. 7 is a diagram illustrating a correlation analyzer, a data signal modulator, and an on-duty ratio modulator of FIG. 6.

8 is a view showing an image quality processing unit of the liquid crystal display according to the third embodiment of the present invention.

9 is a diagram illustrating a correlation analyzer, a data signal modulator, and an on-duty ratio modulator of FIG. 8.

Claims (10)

A liquid crystal panel displaying an image; A backlight for supplying light to the liquid crystal panel; An on duty ratio calculation unit for calculating an input on duty ratio of the input dimming signal; A data signal analysis unit for calculating a gray scale distribution characteristic value of the input data signal input in the frame unit; A first modulation coefficient and a default value are generated according to the correlation analysis between the input on duty ratio and the gray distribution characteristic value, and the second modulation is selected by selecting the first modulation coefficient / default value according to each of advanced mode on / off. A correlation analysis unit outputting as a coefficient; When the first modulation coefficient is input, the data signal is output by performing modulation on the gradation of the input data signal, and when the default value is input, the data signal outputting a data signal having the same gradation as the input data signal. A modulator; On-duty outputs a dimming signal by modulating the input on-duty ratio when the first modulation coefficient is input, and outputs a dimming signal corresponding to the input-on-duty ratio when the default value is input. A non-modulation unit; A first selection switch for selecting and outputting the data signal / the input data signal output from the data signal modulator according to each of the advanced mode on / off; A second selection switch for selecting and outputting a dimming signal / the input dimming signal output from the on-duty ratio modulator according to each of the advanced mode on / off; An inverter circuit unit controlling brightness of the backlight according to an on duty ratio of the dimming signal output from the second selection switch, The first modulation coefficient of the current frame is generated by reflecting the second modulation coefficient of the previous n frames, When the input on duty ratio is modulated to decrease in response to the first modulation coefficient, the gray level of the input data signal is modulated to increase. LCD display device. The method of claim 1, The correlation analysis unit, A correlation analysis block for outputting a first modulation coefficient according to the correlation analysis between the input on duty ratio and the gray scale distribution characteristic value; A default block for outputting the default value; A third selection switch for selecting the first modulation coefficient / default value according to each of the on / off modes of the advanced mode and outputting the second modulation coefficient as the second modulation coefficient; Liquid crystal display comprising a. The method of claim 1, The data signal modulator, When the first modulation coefficient is input, the data signal is output by performing modulation on the gradation of the input data signal, and when the default value is input, the data signal outputting a data signal having the same gradation as the input data signal. A modulation block; A fourth selection switch for selecting and outputting the data signal / the input data signal output from the data signal modulation block according to each of the advanced mode on / off Liquid crystal display comprising a. The method of claim 1, The on duty ratio modulator, On-duty ratio modulation block outputs the same on-duty ratio as the input on-duty ratio when the first modulation coefficient is input by performing modulation on the input on-duty ratio; and; A fifth selection switch for selecting and outputting an on duty ratio / the input on duty ratio output from the on duty ratio modulation block according to each of the advanced mode on / off Liquid crystal display comprising a. The method of claim 1, The gray scale distribution characteristic value includes a target gray scale, As the target gradation decreases, an amount of decreasing the input on duty ratio in response to the first modulation coefficient increases. The target gradation is the maximum gradation of the gradation distribution excluding the upper x% from the gradation distribution of the input data signal. LCD display device. Calculating an input on duty ratio of the input dimming signal; Calculating a gray scale distribution characteristic value of the input data signal input in units of frames; A first modulation coefficient and a default value are generated according to the correlation analysis between the input on duty ratio and the gray distribution characteristic value, and the second modulation is selected by selecting the first modulation coefficient / default value according to each of advanced mode on / off. Outputting as a coefficient; In the data signal modulator, when the first modulation coefficient is input, the data signal is output by performing modulation on the gray level of the input data signal, and when the default value is input, data having the same gray level as the input data signal. Outputting a signal; In the on-duty ratio modulator, when the first modulation coefficient is input, modulate the input on-duty ratio to output a dimming signal, and when the default value is input, dimming corresponding to the input on-duty ratio. Outputting a signal; Selecting and outputting the data signal / the input data signal output from the data signal modulator according to each of the advanced mode on / off; Selecting and outputting a dimming signal / the input dimming signal output from the on duty ratio modulator according to each of the advanced mode on / off; Adjusting the brightness of the backlight according to the on duty ratio of the selected and output dimming signal; Receiving light from the backlight and displaying an image on the liquid crystal panel; The first modulation coefficient of the current frame is generated by reflecting the second modulation coefficient of the previous n frames, When the input on duty ratio is modulated to decrease in response to the first modulation coefficient, the gray level of the input data signal is modulated to increase. Liquid crystal display driving method. The method of claim 6, And in the data signal modulator, selecting and outputting the input data signal when the advanced mode is turned off. The method of claim 6, And outputting a dimming signal corresponding to the input on duty ratio by selecting the input on duty ratio in the on duty ratio modulator when the advanced mode is off. The method of claim 6, The gray scale distribution characteristic value includes a target gray scale, As the target gradation decreases, an amount of decreasing the input on duty ratio in response to the first modulation coefficient increases. The target gradation is the maximum gradation of the gradation distribution excluding the upper x% from the gradation distribution of the input data signal. Liquid crystal display driving method. The method of claim 6, And x% is 50% or less.

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