KR20080062848A - Liquid crystal display device and method of driving the same - Google Patents

Abstract

An LCD device and a driving method thereof are provided to increase the duty rate of lamps corresponding to the central area of a screen and decrease the duty rate of lamps corresponding to the upper and lower areas of the screen, thereby compensating luminance and improving the quality of subtitle broadcasting. An LCD(Liquid Crystal Display) panel(10) displays an image. A gate driving unit(20) and a data driving unit(30) supply a driving signal and a data signal to the LCD panel. A timing control unit(70) generates a control signal used in the gate driving unit, a vertical start signal for lighting a lamp(40), and a control signal for turning on/off the lamp at difference duty rates. A backlight unit includes the lamp and an inverter(50). The lamps supply a light source to the LCD panel. The inverter drives lamps. The timing control unit includes a control signal generator(80) for generating the control signal for turning on/off the lamps at different duty rates. The lamp includes plural fluorescent lamps. The on/off duty rates of fluorescent lamps corresponding to the upper and lower areas of an image frame displayed on the LCD panel are smaller than the on/off duty rates of fluorescent lamps corresponding to the central area of the image frame displayed on the LCD panel.

Description

Liquid crystal display and its driving method {LIQUID CRYSTAL DISPLAY DEVICE AND METHOD OF DRIVING THE SAME}

1 is a block diagram showing the structure of a liquid crystal display according to the present invention.

2 is a block diagram illustrating driving of a backlight unit according to the present invention.

3 is a view showing a driving state of the scanning lamp of the backlight unit according to the present invention.

4A is a diagram illustrating a luminance distribution of a backlight unit according to the related art.

4B is a diagram illustrating a luminance distribution of a backlight unit according to the present invention.

* Description of the symbols for the main parts of the drawings *

10: liquid crystal display panel 20: gate driver

30: gator drive 40: lamp

60: voltage generator 70: timing controller

80: control signal generator

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a driving method thereof capable of improving image quality.

Liquid crystal display device (Liquid crystal display device) is due to the characteristics such as light weight, thin, low power consumption driving, the application range is gradually increasing. In accordance with this trend, the liquid crystal display device is used for office automation equipment, audio / video equipment, and the like. On the other hand, the liquid crystal display device displays the desired image on the screen by adjusting the transmission amount of the light beam according to the image signal applied to the plurality of control switches arranged in a matrix form.

While the cathode ray tube (CRT) is an impulse light emission by scanning an electron gun, since the liquid crystal display device is a hold light emission using a backlight system using a linear lamp (fluorescent lamp) as an illumination light source, it is difficult to display a complete moving image. That is, when moving picture display is performed with a liquid crystal display device, so-called motion blurring (image outline deterioration) occurs due to the hold characteristic, and image quality is deteriorated.

Accordingly, a liquid crystal display device according to a backlight sequential driving method using a direct type backlight in which a plurality of lamps are arranged horizontally in order to prevent motion blur (moving image contour deterioration) of a moving image display has been disclosed.

The liquid crystal display device according to the backlight sequential driving method applies a dimming function to adjust the brightness of the lamps when the plurality of lamps are turned on in synchronization with the start time of the scanning signal of the display image in response to a request for high display quality. Doing.

This dimming function is particularly useful for displaying movies. In order to adjust the brightness of the lamp, there are a method of changing the intensity of the current flowing through the lamp, and a method of changing the lamp on / off duty ratio while keeping the magnitude of the lamp current constant.

If the lamp duty ratio is small, the motion picture response time (MPRT) is improved, but the luminance is lowered. Especially when moving at a constant speed, a motion blur phenomenon is easily recognized. Therefore, when driving the backlight unit according to a conventional scanning method, a motion blur phenomenon occurs in caption broadcasting that is broadcast at a constant speed due to high luminance at the top and bottom of the screen.

According to the present invention, the on / off duty ratio of the lamps corresponding to the center area of the screen is increased to compensate for luminance, while the on / off duty ratio of the lamps corresponding to the top and bottom areas of the screen is reduced to improve the quality of closed captioning. It is an object of the present invention to provide a liquid crystal display and a driving method thereof.

In order to achieve the above object, the liquid crystal display device according to the present invention,

A liquid crystal display panel displaying an image;

A gate driver supplying a driving signal and a data signal to the liquid crystal display panel;

A data driver;

A timing controller for generating a control signal used in the gate driver and the data driver, a vertical start signal (STV) for turning on a lamp, and a control signal for turning on / off lamps at different duty ratios; And

A backlight unit including a lamp for supplying a light source to the liquid crystal display panel and an inverter driving the same;

The timing controller includes a control signal generator for generating a control signal to turn on / off lamps at different duty ratios.

According to another aspect of the present invention, there is provided a method of driving a liquid crystal display device.

A liquid crystal display panel displaying an image;

A gate driver and a data driver supplying a driving signal and a data signal to the liquid crystal display panel;

A timing controller for generating a control signal used in the gate driver and the data driver, a vertical start signal (STV) for turning on a lamp, and a control signal for turning on / off lamps at different duty ratios;

A backlight unit including a plurality of fluorescent lamps for supplying a light source to the liquid crystal display panel and an inverter driving the same; And

The timing controller includes a control signal generator for generating a control signal to turn on / off the lamps at different duty ratios.

The lamps are sequentially driven according to different lamp on / off duty ratios.

According to the present invention, the on / off duty ratio of lamps corresponding to the center area of the screen is increased to compensate for luminance while the on / off duty ratio of lamps corresponding to the top and bottom areas of the screen is reduced to improve the quality of closed captioning. It was.

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

1 is a block diagram showing the structure of a liquid crystal display according to the present invention.

Referring to FIG. 1, a liquid crystal display according to the present invention includes a liquid crystal display panel 10, a gate driver 20, a data driver 30, a lamp 40, an inverter 50, a voltage generator 60, and the like. The timing controller 70 is included. The lamp 40 and the inverter 50 are backlight units, and in the case of the direct type backlight unit, the lamp 40 includes a plurality of fluorescent lamps. The fluorescent lamp includes a cold cathode tube fluorescent lamp or an external electrode fluorescent lamp.

The liquid crystal display panel 10 includes a substrate on which a pixel pattern is formed, and a plurality of gate lines and a plurality of data lines perpendicular to the gate lines are formed on the substrate, and the gate lines and the data lines are formed on the substrate. The pixel is formed at the intersection of. Each pixel is arranged in a matrix form. Each pixel includes a thin film transistor having a gate electrode and a source electrode connected to a gate line and a data line, and a pixel capacitor and a storage capacitor connected to a drain electrode of the thin film transistor.

In such a pixel structure, when a gate voltage for sequentially selecting each gate line is applied by the gate driver 20, a thin film transistor of a pixel connected to the corresponding gate line is turned on, and then each data driver 30 is turned on by the data driver 30. An image data voltage including pixel information is applied to the data line. This voltage is applied to the pixel capacitor and the sustain capacitor through the thin film transistor of the pixel, and these capacitors are driven to perform a predetermined display operation.

The timing controller 70 receives RGB image data (RGB data), vertical and horizontal sync signals (Vsync / Hsync), and a clock signal (CLK) input from an external graphic source (not shown). Basically, the timing controller 70 converts a format of the input RGB image data RGB data according to a data format required by the data driver 30, and the liquid crystal display panel 10. To generate and output a control signal to be used by the gate driver 20 and the data driver 30. In addition, the timing controller 70 outputs a vertical start signal (STV) to the inverter 50. The vertical start signal STV is a frame period signal when an initial signal is applied to a gate line. Therefore, a plurality of fluorescent lamps included in the lamp 40 are sequentially turned on and off with the vertical start signal STV as a starting point.

In addition, the timing controller 70 of the present invention includes a control signal generator 80 that controls the duty ratio to have a specific luminance value while sequentially turning on and off the plurality of fluorescent lamps provided in the lamp 40. Include. The control signal generator 80 generates the first, second, and third control signals Vdim1, Vdim2, and Vdim3 capable of controlling the luminance of the fluorescent lamps while repeatedly turning on and off the fluorescent lamps in units of one frame.

The first control signal Vdim1 is a signal for controlling the duty ratio of the fluorescent lamps corresponding to the upper region of the image frame, and the second control signal Vdim2 is a duty ratio of the fluorescent lamps corresponding to the center region of the image frame. The third control signal Vdim3 is a signal for controlling the duty ratio of the fluorescent lamps corresponding to the lower region of the image frame.

The present invention improves MPRT characteristics by lowering the lamp on / off duty ratio in the upper and lower regions of the video frame during which caption broadcasting is performed, while increasing the lamp on / off duty ratio in the center region of the video frame to compensate for luminance. It was.

The voltage generator 60 generates and outputs a gray voltage Vgray and a gate voltage Vgate, which are voltages actually applied to the data line and the gate line of the liquid crystal display panel 10, respectively. Here, the gray voltage Vgray has a plurality of voltage levels and is transmitted to the data driver 30. The gate voltage Vgate includes a gate on voltage and a gate off voltage, and is transmitted to the gate driver 20.

The gate driver 20 includes a plurality of gate driver ICs (not shown) respectively responsible for a predetermined number of gate lines on the liquid crystal display panel 10, and the control signal CONT provided from the timing controller 70. ) And each gate line on the liquid crystal display panel 10 are sequentially scanned in units of one horizontal scanning period by using the gate voltage Vgate provided from the voltage generator 60. For example, the gate driver 20 applies a gate-on voltage to the gate line to be scanned and a gate-off voltage to the remaining gate lines, and the application time of the gate-on voltage is one horizontal scanning period. This scanning process is performed sequentially for all gate lines.

The data driver 30 includes a plurality of data driver ICs (not shown) each responsible for a predetermined number of data lines on the liquid crystal display panel 10. The data driver 30 sequentially latches the RGB image data (RGB data) supplied from the timing controller 70 to change the data sequence of the point sequential method into a line sequential method, and to match each image data. The gray voltage Vgray is selected, and the selected voltages are applied to each data line on the liquid crystal display panel 10 as an image data voltage in units of one horizontal scanning period. One screen, that is, a frame, is divided by a pulse of the vertical start signal STV, and the above-described operation in the data driver 30 is continuously performed for one frame in units of one horizontal scanning period. This operation is also repeated for every frame.

The inverter 50 uses the control signals Vdim1, Vdim2, and Vdim3 output from the control signal generator 80 of the timing controller 70 and the vertical start signal STV output from the timing controller 70. A lamp driving signal is generated, and the lamp driving signal controls the lighting of the fluorescent lamps of the lamp 40 installed on the rear surface of the liquid crystal display panel 10. The control signals Vdim1, Vdim2, and Vdim3 may be provided by the timing controller 70 or may be provided by an external display-related peripheral board. The lamp driving signal has a turn-on and turn-off period, and in the present invention, the duty ratio of the lamps at the top and bottom of the backlight unit and the lamps at the center area are differently adjusted to improve the screen quality.

2 is a block diagram illustrating driving of a backlight unit according to the present invention.

Referring to FIG. 2, control signals Vdim1, Vdim2, and Vdim3 and a vertical start signal STV supplied from the timing controller of the liquid crystal display are supplied to the control IC 51 of the inverter 50.

The control IC 51 compares the control signals Vdim1, Vdim2, and Vdim3 with pulse signals generated by an internal PWM signal generator to correspond to a lamp driving signal corresponding to an upper region of an image frame and a center region of an image frame. A ramp driving signal corresponding to the ramp driving signal and a lower region of the image frame are generated.

The lamp driving signals generated from the control IC 51 are first, second, third, fourth, fifth, sixth, seventh and eighth driving units 52a, 52b, 52c, 52d, 52e, 52f, 52g of the inverter 50, respectively. , 52h) to sequentially light up the fluorescent lamps Lamp1, Lamp2, Lamp3, Lamp4, Lamp5, Lamp6, Lamp7, Lamp8.

For example, a lamp driving signal having a lamp duty ratio of 5 to 10% is input to the first and second driving units 52a and 52b, and a lamp is supplied to the third, 4, 5 and 6 driving units 52c, 52d, 52e, and 52f. The duty ratio is input to the lamp driving signal of the reference duty ratio (40 to 70%) of the liquid crystal display, and the lamp driving signal of 10 to 20% of the lamp duty ratio is input to the seventh and eighth driving units 52g and 52h.

Accordingly, since the lamp duty ratio is lower than the center region at the top and bottom of the image frame, the MPRT is improved to implement high quality closed caption broadcasting, and the screen quality can be improved by compensating for luminance characteristics in the center region.

3 is a view showing a driving state of the scanning lamp of the backlight unit according to the present invention.

Referring to FIG. 3, when a vertical start signal STV for dividing each image frame is applied to a liquid crystal display panel, gate out signals are sequentially applied to gate lines of the liquid crystal display panel corresponding to one frame. ) Is applied.

At this time, the plurality of fluorescent lamps (lamp1, lamp2, lamp3, lamp4, lamp5, lamp6, lamp7, lamp8) arranged in the backlight unit are sequentially driven in accordance with the driving signal is applied to the gate line.

In the present invention, the duty ratio of the first and second fluorescent lamps is lowered to 5-10% so that when the duty ratio is not generally lowered, the fluorescent lamp is turned on only for a shorter time (t1).

In addition, the duty ratio of the third, fourth, fifth, and sixth fluorescent lamps was slightly higher than the conventional (duty ratio 40-70%) to light up the lighting time of the fluorescent lamps longer than the first and second (t2).

The duty ratio of the seventh and eighth fluorescent lamps was reduced to 10-20% so that the fluorescent lamps were turned on for a shorter time (t3) than when the duty ratio was not lowered.

Accordingly, in the present invention, motion blur does not occur in caption broadcasting at the top and bottom of the image frame, and a high quality screen having improved luminance can be implemented in the center region of the image frame.

4A is a diagram illustrating a luminance distribution of a backlight unit according to the prior art, and FIG. 4B is a diagram illustrating a luminance distribution of a backlight unit according to the present invention.

As shown in FIGS. 4A and 4B, the conventional backlight unit has high luminance in the upper region and the lower region and lower luminance than the reference in the central region.

However, as in the present invention, the lamp duty ratio of the fluorescent lamps at the top and bottom of the backlight unit corresponding to the upper area of the image frame is lowered, and the lamp duty ratio of the fluorescent lamps at the center of the backlight unit corresponding to the center area of the image frame is increased. It was made to have uniform luminance characteristic as a whole.

In particular, in the prior art, since the luminance is high in the upper and lower regions of the image frame, a motion blur phenomenon occurs during caption broadcasting. In the present invention, the fluorescent lamps of the backlight unit are individually driven by setting a duty ratio, thereby eliminating motion blur in the upper and lower regions of the image frame.

As described in detail above, the present invention corresponds to the screen center area.

The duty ratio of the lamps is increased to compensate for luminance, and the duty ratio of the lamps corresponding to the upper and lower regions of the screen is reduced to improve the quality of closed captioning.

The present invention has the effect of having a uniform brightness characteristics by adjusting the on / off duty ratio of the lamps.

The present invention is not limited to the above-described embodiments, and various changes can be made by those skilled in the art without departing from the gist of the present invention as claimed in the following claims.

Claims (6)

A liquid crystal display panel displaying an image; A gate driver and a data driver supplying a driving signal and a data signal to the liquid crystal display panel; A timing controller for generating a control signal used in the gate driver and the data driver, a vertical start signal (STV) for turning on a lamp, and a control signal for turning on / off lamps at different duty ratios; And A backlight unit including a lamp for supplying a light source to the liquid crystal display panel and an inverter driving the same; And the timing controller includes a control signal generator which generates a control signal to turn on / off lamps at different duty ratios. The display device of claim 1, wherein the lamp includes a plurality of fluorescent lamps, and on / off duty ratios of fluorescent lamps corresponding to upper and lower regions of an image frame displayed on the LCD panel are displayed on the LCD panel. And an on / off duty ratio of the fluorescent lamps corresponding to the center region of the image frame. A liquid crystal display panel displaying an image; A gate driver and a data driver supplying a driving signal and a data signal to the liquid crystal display panel; A timing controller for generating a control signal used in the gate driver and the data driver, a vertical start signal (STV) for turning on a lamp, and a control signal for turning on / off lamps at different duty ratios; A backlight unit including a plurality of fluorescent lamps for supplying a light source to the liquid crystal display panel and an inverter driving the same; And The timing controller includes a control signal generator for generating a control signal to turn on / off the lamps at different duty ratios. And the lamps are sequentially driven according to different lamp on / off duty ratios. The display device of claim 3, wherein the on / off duty ratios of the fluorescent lamps corresponding to the upper and lower regions of the image frame displayed on the liquid crystal display panel are determined by the fluorescent lamps corresponding to the center area of the image frame displayed on the liquid crystal display panel. A liquid crystal display device driving method, characterized in that it is smaller than the on / off duty ratio. The method of claim 4, wherein the on / off duty ratio of the fluorescent lamps corresponding to the upper and lower regions of the image frame displayed on the liquid crystal display panel is 10 to 20%. 4. The method of claim 3, wherein the fluorescent lamps are sequentially driven according to different lamp on / off duty ratios so that the luminance characteristics of the backlight unit have uniform luminance characteristics in all areas.

Images