KR20080041908A - Liquid crystal display and driving method thereof - Google Patents

Abstract

An LCD device and a driving method thereof are provided to block a gradation voltage from being inputted to a pixel when black data is inputted, and enable the pixel of a normal block mode to display a black image, thereby displaying a more complete black image to improve the contrast ratio of a displayed image. An LCD(Liquid Crystal Display) panel(400) displays an image according to a data signal and has plural unit pixels for displaying a black image when there is no data signal. A data driving unit(540) provides the data signal to the LCD panel as an image signal. A gate driving unit(530) provides a gate signal to the LCD panel as a switching signal so as for the data signal to be applied to the LCD panel. A signal controller(510) controls the gate driving unit and the data driving unit so as for black data not to be inputted to the LCD panel when the black data is inputted.

Description

Liquid crystal display and its driving method {LIQUID CRYSTAL DISPLAY AND DRIVING METHOD THEREOF}

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

2 is a circuit diagram of a unit pixel of a liquid crystal display according to an exemplary embodiment of the present invention.

3 is an operation timing diagram of a liquid crystal display according to an exemplary embodiment of the present invention.

<Explanation of protection for main parts of drawing>

100: upper substrate 190: pixel electrode

200: lower substrate 230: black matrix

270: common electrode 400: liquid crystal display panel

500: liquid crystal drive circuit 510: signal controller

520: voltage generator 530: gate driver

540: data driver

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 capable of improving a contrast ratio of a liquid crystal display panel driven in a normal black mode and a driving thereof. It is about a method.

In general, a liquid crystal display includes a liquid crystal display panel including an upper substrate on which a black matrix, a color filter, and a common electrode are formed, a lower substrate on which a thin film transistor and a pixel electrode are formed, and a liquid crystal layer filled between two substrates. And a polarizing plate attached to both sides of the liquid crystal display panel. In addition, since the liquid crystal display panel does not emit light by itself, a backlight for providing light is disposed on the rear surface of the liquid crystal display panel so as to visually recognize the display contents. In addition, a driving circuit for controlling the operation of the liquid crystal display panel and the backlight is required.

Here, the liquid crystal display panel displays an image by adjusting the light transmittance of the liquid crystal layer. For example, referring to the liquid crystal display panel of the normal black mode, the arrangement of the liquid crystal molecules by the electric field generated by the difference between the two voltage levels by applying a common voltage to the common electrode and a gray voltage to the pixel electrode The desired image is displayed by changing the light transmittance to adjust the light transmittance. In this case, the gray voltage applied to the pixel electrode depends on the gray level of the input image data. When black data having a gray level of '0' is input, the gray level voltage having the same level as the common voltage is applied. Ideal. However, since electronic devices have an operating error, the gray scale voltage applied to the pixel electrode is changed within a certain range. Therefore, the image in which black data is input and displayed does not display perfect black.

As described above, since the liquid crystal display according to the related art does not display perfect black, the band between the black and the white is narrowed, and as a result, the contrast ratio of the display image is lowered, resulting in poor display quality. .

The present invention was derived to solve the above problems, and when black data is input, the corresponding gray voltage is blocked from being input to the pixels, and instead, the pixels in the normal black mode display the black image by themselves. It is an object of the present invention to provide a liquid crystal display and a driving method thereof capable of improving the contrast ratio of a display image by displaying a black image closer to a more complete black image.

A liquid crystal display device according to the present invention for achieving the above object is a liquid crystal display panel comprising a plurality of unit pixels for displaying the image in accordance with the data signal, and displays a black image when there is no data signal, and the liquid crystal A data driver that provides a data signal as an image signal to a display panel, a gate driver that provides a gate signal as a switching signal so that the data signal can be applied to the liquid crystal display panel, and black data when the black data is input to the liquid crystal display panel And a signal controller configured to control the gate driver and the data driver so that black data is not input.

The signal controller generates a gate clock signal which is a basic operation clock of the gate driver, and when black data is input, disables the gate clock signal and provides the gate clock signal to the gate driver.

According to an aspect of the present invention, there is provided a method of driving a liquid crystal display device, including detecting whether black data exists in image data, and outputting a disabled gate clock signal when black data is detected in the detecting step. Turning off the thin film transistor of the pixel when the gate clock signal disabled in the output step is input; and if the thin film transistor of the pixel is turned off so that no data signal is applied, the pixel itself blocks light. Displaying black.

The disabled gate clock signal may be a signal in which the output level is changed from a high period to a low period or a signal in which the output is stopped for a predetermined time.

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

However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the embodiments are intended to complete the disclosure of the present invention, and to those skilled in the art the scope of the invention. It is provided for complete information. Like reference numerals in the drawings refer to like elements.

1 is a block diagram of a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 2 is a circuit diagram of a unit pixel of a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 1, the liquid crystal display includes a liquid crystal display panel 400 for displaying an image and a liquid crystal drive circuit 500 for controlling an operation of the liquid crystal display panel 400.

The liquid crystal display panel 400 includes a plurality of unit pixels arranged in a matrix form. The unit pixel is defined by a cross region of a plurality of gate lines G ₁ to G _n extending in a substantially row direction and a plurality of data lines D ₁ to D _m extending in a column direction perpendicular thereto. The device Q includes a liquid crystal capacitor Clc connected thereto, and a storage capacitor Cst.

Referring to FIG. 2, the liquid crystal display panel 400 includes a lower substrate 100 having a switching element Q, a gate line G, a data line D, a pixel electrode 190, and a storage electrode (not shown). ), An upper substrate 200 on which a black matrix (not shown), a color filter 230, and a common electrode 270 are formed, and a liquid crystal layer (not shown) filled between the two substrates 100 and 200.

The switching element Q includes amorphous silicon, polysilicon, or the like as a channel layer, and includes a thin film transistor (TFT) including a gate electrode, a source electrode, and a drain electrode. It is effective to use In this case, the gate electrode is connected to the gate line G, the source electrode is connected to the data line D, and the drain electrode is connected to the pixel electrode 190.

The pixel electrode 172 forms a liquid crystal capacitor Clc together with the common electrode 270 positioned on the pixel electrode 172. The liquid crystal capacitor Clc controls the molecular arrangement of the liquid crystal layer by charging the data signal.

The storage electrode (not shown) forms a storage capacitor Cst together with the pixel electrode 172 positioned thereon. The sustain capacitor Cst charges the data signal to hold the data signal for a predetermined period, for example, for a predetermined frame (usually one frame). Of course, the storage capacitor (C _st ) that serves as an auxiliary role of the liquid crystal capacitor (C _lc ) may be omitted.

A gray voltage, that is, a data signal, is applied to the pixel electrode 190 of the liquid crystal display panel 400, and a common voltage is applied to the common electrode 270, thereby adjusting the light transmittance of the liquid crystal layer filled therebetween. An image is displayed. In the liquid crystal display panel 400 of the present exemplary embodiment, a normal black mode in which a liquid crystal layer blocks light incident from the rear surface in a normal state in which a data signal is not applied to the pixel electrode 190 is displayed. It is effective to use the liquid crystal display panel 400 in the normal black mode.

Meanwhile, the liquid crystal driving circuit 500 including the signal controller 510, the voltage generator 520, the gate driver 530, and the data driver 540 is provided outside the liquid crystal display panel 400 described above. Various signals for the operation of the liquid crystal display panel 400 are provided through the liquid crystal driving circuit 500.

Here, the gate driver 530 and the data driver 540 may be directly formed on the lower substrate of the liquid crystal display panel 400 (ASG method), and are separately manufactured so that the chip on board (COB) and tape automated bonding (TAB) are manufactured. ), And may be mounted on the lower substrate in a manner such as a chip on glass (COG). Preferably, the gate driver and the data driver of the present embodiment are manufactured in the form of at least one driving chip and mounted on the lower substrate. In addition, the signal controller 510 and the voltage generator 520 are mounted on a printed circuit board (PCB), and the gate driver 530 and the data driver through a flexible printed circuit (FPC). It is preferably connected to the 540, and electrically connected to the liquid crystal display panel 400.

The signal controller 510 receives an input image signal and an input control signal from an external graphic controller (not shown). For example, an input image signal including the input image data R, G, and B, and a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a main clock MCLK, and a data enable signal DE are included. Is provided with an input control signal. In addition, the signal controller 510 generates an internal image signal, that is, internal image data R ', G', and B 'based on the input image signal, and based on the input control signal, The gate control signal CS1 including the vertical synchronization start signal STV and the gate clock signal CPV to control the operation of the gate driver 530, and the horizontal synchronization start signal STH to control the operation of the data driver 540. And a data control signal CS2 including the data load signal LOAD.

The voltage generator 520 generates and outputs various driving voltages for driving the liquid crystal display panel 400 using an external power source input from an external power supply device (not shown). For example, a gate-on voltage Von for turning on the switching element Q and a gate-off voltage Voff for turning off the switching element Q are generated and gated. The controller 530 outputs the gradation voltage Vgray and the common voltage Vcom that may correspond to the gradation level, and outputs the gradation voltage Vgray and the common voltage Vcom to the data driver 540.

The gate driver 530 starts an operation according to the vertical synchronization start signal STV, and the gate on voltage Von and the gate off voltage Voff input from the voltage generator 520 according to the gate clock signal CPV. The gate signal of the analog form including the light is sequentially output to the plurality of gate lines G ₁ to G _n formed in the liquid crystal display panel 400. In this case, the gate on voltage Von is output in the high section of the gate clock signal CPV, and the gate off voltage Voff is output in the low section of the gate clock signal CPV. .

The data driver 540 converts the internal image data input from the signal controller 510, that is, the digital image data R ', G', and B ', using a plurality of levels of grayscale voltages input from the voltage generator. And converts the data signal into a plurality of data lines D1 through Dm formed in the liquid crystal display panel according to the load signal.

A general driving method of the liquid crystal display according to the present exemplary embodiment having such a configuration will be described below.

The signal controller 510 generates a gate control signal CS1 and provides the gate control signal CS1 to the gate driver 530, and generates internal image data R ′, G ′, and B ′ and a data control signal CS2. 540). In this case, it is preferable that the internal image data R ', G', and B 'is provided digitally. The internal image data R ', G', and B 'may be corrected image data generated by correcting the raw image data R, G and B through a predetermined algorithm.

The gate driver 530 applies a gate-on voltage Von to the first gate line G ₁ to turn on the switching elements Q connected to the corresponding gate line G ₁ , so that the first data signal is applied to the gate driver 530. The first scan line.

The data driver 540 sequentially receives the internal image data R ', G', and B ', and applies the gray level of each image data R', G ', and B' among the plurality of levels of gray voltage Vgray. A corresponding gray voltage is selected and applied to the scan line as a data signal. In this case, it is preferable to simultaneously apply data signals corresponding to one line to the scan line, but it is also possible to sequentially apply data signals corresponding to one pixel.

In this manner, all the gate lines G ₁ to G _n are sequentially scanned during one frame to apply data signals to all the pixels, and the next frame is started when the corresponding frame ends. In order to prevent deterioration of the liquid crystal layer, a data signal in which the polarity of the common voltage Vcom is inverted may be applied to some pixels or all pixels. For example, the signal controller 510 outputs an inversion signal RVS for inverting the polarity of the data signal with respect to the common voltage Vcom, and the data driver 540 for each frame using the inversion signal (frame inversion). Or a data signal whose polarity is inverted line by line (line inversion) or pixel by pixel (dot inversion).

Meanwhile, all pixels of the liquid crystal display panel 400 are charged with respective voltages under the control of the liquid crystal driving circuit 500 to form an electric field in the liquid crystal layer. That is, data signals having a potential of a suitable level are applied to the pixel electrode 190, and a common voltage Vcom is applied to the common electrode 270 to form an electric field between the two electrodes 190 and 270. As a result, the molecular arrangement of the liquid crystal layer is changed to change the transmittance of light incident from the rear surface. Subsequently, the light provided from the backlight (not shown) positioned on the rear surface of the liquid crystal display panel 400 passes through the liquid crystal layer, and the upper substrate 200 on which red (R), green (G), and blue (B) are disposed. ) Is colored by a color filter (not shown) and emitted to the front surface, and the light emitted from each pixel is mixed to realize a color image.

On the other hand, the signal controller 510 of the liquid crystal display having the above configuration inputs the corresponding data to the corresponding pixel when the internal image data R ', G', B 'to be output to the data driver 540 is black data. By not making it possible, the pixel can be controlled to display black in the normal state. As a result, the contrast ratio can be improved by displaying the black closer to the perfect black, which will be described below with reference to FIGS. 1 and 3. 3 is an operation timing diagram of the liquid crystal display according to the exemplary embodiment of the present invention.

The signal controller 510 detects whether black data exists in the internal image data R ', G', and B 'to be output. At this time, if black data is detected, the disabled gate clock signal CPV is output. For example, when the corresponding image data is represented by an 8-bit gradation level, the black data is represented as '00000000' as binary data, and black data having a gradation level of '00000000' is detected in the Nth image data. The gate clock signal CPV disabled by switching the output from a high level to a low level in a corresponding period N or by stopping the output for a predetermined time. Will print

The gate driver 530 operates according to the vertical synchronization start signal STV, and sequentially outputs gate signals to the plurality of gate lines G ₁ to G _n in the rising edge period of the gate clock signal CPV. Since the disabled gate clock signal CPV is input in the section N where the black data is output, the switching element Q of the pixels connected to the corresponding gate line G is turned off. Therefore, the data signals output from the data driver 540 are not applied to the pixels connected to the corresponding gate line G, so that the pixels are in a normal state to display black.

In general, the liquid crystal display panel of the normal black mode does not apply the gray voltage to the pixel than to display the black by applying the gray level corresponding to the black data, that is, the '00000000' value. Displays a picture close to perfect black in the normal state. Therefore, since the gradation band between black and white becomes wider, the contrast ratio of the display image can be remarkably improved.

As mentioned above, although this invention was demonstrated with reference to the above-mentioned Example and an accompanying drawing, this invention is not limited to this, It is limited by the following claims. Therefore, one of ordinary skill in the art will appreciate that the present invention can be variously modified and modified without departing from the technical spirit of the following claims.

As described above, according to the present invention, when the black data is input, the gray level voltage corresponding thereto is prevented from being input to the pixels, and instead, the pixels in the normal black mode display the black image by themselves, thereby making the black image more complete. Display close to black image. As a result, since the gradation band between black and white becomes wider, the contrast ratio of the display image can be remarkably improved.

Claims (5)

A liquid crystal display panel which displays a corresponding image according to a data signal, and includes a plurality of unit pixels which display a black image when there is no data signal; A data driver for providing a data signal as an image signal to the liquid crystal display panel; A gate driver providing a gate signal as a switching signal so that the data signal is applied to the liquid crystal display panel; And a signal controller configured to control the gate driver and the data driver so that black data is not input to the liquid crystal display panel when black data is input. The method according to claim 1, The signal control unit, And a gate clock signal which is a basic operation clock of the gate driver, and when black data is input, disables the gate clock signal and provides the gate clock signal to the gate driver. Detecting whether black data exists in the image data; Outputting a disabled gate clock signal when black data is detected in the detecting step; Turning off the thin film transistor of the pixel when the disabled gate clock signal is input in the output step; If the thin film transistor of the pixel is turned off so that a data signal is not applied, the pixel itself blocks light and displays black. The method according to claim 3, In the output step, And wherein the disabled gate clock signal is configured to switch an output level from a high period to a low period. The method according to claim 3, In the output step, And the output of the disabled gate clock signal is stopped for a predetermined time.

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