KR100739621B1 - Liquid crystal display and driving method thereof - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a driving method thereof, wherein the device includes a liquid crystal display panel including a plurality of pixels, a gate driver, a gray voltage generator, a data driver, a timing controller, and a driving voltage for driving the gate driver. And generating and applying the generated power to the gate driver according to the power enable signal. At this time, the power generator applies a driving voltage to the gate driver when the power enable signal is at a high level, and blocks the driving voltage when the power is enabled. According to the present invention, by making the power enable signal active high, the output voltage of the gate driver can be removed quickly, thereby eliminating the afterimage.

Liquid crystal display, field sequential driving, power generator, power enable signal, gate driver

Description

Liquid crystal display and driving method thereof {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 an equivalent circuit diagram of one pixel of a liquid crystal display according to an exemplary embodiment of the present invention.

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

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

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 having a field sequential driving method and a driving method thereof.

Recently, display devices are also required to be lighter and thinner in accordance with the light weight and thickness of personal computers and televisions, and according to such demands, flat panels such as liquid crystal displays (LCDs) instead of cathode ray tubes (CRTs) are required. Display is being developed.

The liquid crystal display device applies an electric field to a liquid crystal material having an anisotropic dielectric constant injected between two substrates, and adjusts the intensity of the electric field to control the amount of light transmitted from the external light source (backlight) to the substrate. It is a display device which obtains a desired image signal.

Such a liquid crystal display is representative of a portable flat panel display, and among these, a TFT-LCD using a thin film transistor (TFT) as a switching element is mainly used.

In general, the liquid crystal display may be classified into two methods, a color filter method and a field sequential driving method, according to a method of displaying a color image.

A color filter type liquid crystal display device forms a color filter layer consisting of three primary colors of red (R), green (G), and blue (B) on one of two substrates, and adjusts the amount of light transmitted through the color filter layer. By doing so, a desired image is displayed. The color filter type LCD synthesizes R, G, and B colors by adjusting the amount of light transmitted through the R, G, and B color filter layers in transmitting light emitted from a single light source to the R, G, and B color filter layers. By doing so, a desired image is displayed.

As described above, in a liquid crystal display device that displays an image using a single light source and a three-color color filter layer, a corresponding unit pixel is required for each of the R, G, and B regions, so that three times as many pixels are used as for displaying black and white. It is necessary. Therefore, in order to obtain a high resolution image, sophisticated manufacturing technology of a liquid crystal display panel is required. In addition, such a liquid crystal display device has manufacturing difficulties in that a separate color filter layer is formed on a substrate, and the luminance is lowered because the light transmittance of the color filter itself is low.

The liquid crystal display of the field sequential driving method periodically turns on independent light sources of R, G, and B colors, and applies a color signal corresponding to each pixel in synchronization with the lighting cycle to generate a full color image. Get That is, according to the liquid crystal display of the field sequential driving method, R, G, and B primary colors output from R, G, and B backlights are output to one pixel without dividing one pixel into R, G, and B unit pixels. By displaying the light sequentially in time division, an image is displayed using the afterimage effect of the eye.

Such a field sequential driving method may be classified into an analog driving method and a digital driving method.

The analog driving method sets a plurality of gray voltages corresponding to the number of gray scales to be displayed, selects one gray voltage corresponding to gray data among the gray voltages, and drives the liquid crystal panel with the selected gray voltage to thereby apply the applied gray voltage. The gradation is displayed by the corresponding amount of transmitted light.

On the other hand, in the digital driving method, the driving voltage applied to the liquid crystal is made constant, and the voltage application time is controlled to display the gray scale. According to such a digital driving method, gray scales are displayed by adjusting a cumulative amount of light transmitted through a liquid crystal by maintaining a constant driving voltage and controlling a voltage application state and a voltage non-application state in a timing manner.

However, when the power is unexpectedly cut off in such a liquid crystal display device, an afterimage remains on the display screen, thereby degrading the quality of the liquid crystal display device.

Accordingly, an object of the present invention is to provide a liquid crystal display device and a driving method thereof, in which an afterimage remains on the display screen even when the power is unexpectedly cut off.

The liquid crystal display according to an embodiment of the present invention for achieving the technical problem,

And a plurality of scan lines for transmitting a scan signal, a plurality of data lines insulated from and intersecting the scan lines, and a plurality of pixels formed in an area surrounded by the scan lines and data lines, respectively, and connected to the scan lines and data lines. Liquid crystal display panel,

A gate driver for sequentially supplying scan signals to the scan lines;

A gray voltage generator for generating gray voltage corresponding to gray data;

A data driver for supplying a gray voltage output from the gray voltage generator to a corresponding data line;

A timing controller which transmits the gray data to the gray voltage generator, and controls the gate driver and the data driver;

A power generation unit generating a driving voltage for driving the gate driver and applying the driving voltage to the gate driver according to a power enable signal.

It includes.

In this case, the power generation unit applies the driving voltage to the gate driver when the power enable signal is at a high level, and blocks the driving voltage when the power is enabled at a low level. The power enable signal is changed to the low level when the power is cut off in a state where the power enable signal is set to the high level during normal operation.
The power enable signal may be transmitted from the timing controller to the power generator.

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The power enable signal may be transmitted from the data driver to the power generator.

Furthermore, the pixel further includes a plurality of light sources that respectively output red, green, and blue light.

It is preferable that each said light source turns on one by one.

In addition, according to another embodiment of the present invention for achieving the technical problem, a liquid crystal display including a liquid crystal display panel, a gate driver for applying a scan signal to the liquid crystal display panel, and a power generation unit for applying a driving voltage to the gate driver The driving method of the device is

Applying a power enable signal to the power generation unit, and

Applying the driving voltage to the gate driver according to the power enable signal

Including;

The driving voltage is applied when the power enable signal is at a high level, and the driving voltage is blocked when the power enable signal is at a low level. The power enable signal is changed to the low level when the power is cut off in a state where the power enable signal is set to the high level during normal operation.

The method may further include sequentially lighting red, green, and blue light sources on the liquid crystal display panel.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like parts are designated by like reference numerals throughout the specification.

A liquid crystal display and a driving method thereof according to an embodiment of the present invention will now be described in detail with reference to the drawings.

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

As shown in FIG. 1, the liquid crystal display according to the exemplary embodiment of the present invention includes a liquid crystal display panel 100, a gate driver 200, a data driver 300, a gray voltage generator 400, and a timing controller 500. ), Light emitting diodes 600a, 600b, and 600c that output R, G, and B light, respectively, and a light source controller 700.

The liquid crystal display panel 100 includes a plurality of display signal lines S1 -Sn and D1 -Dm and a plurality of pixels connected to the plurality of display signal lines S1-Sn and D1-Dm in an equivalent circuit and arranged in a substantially matrix form.

The display signal lines S1 -Sn and D1 -Dm include a plurality of scan lines S1 -Sn for transmitting a gate signal (also referred to as a "scan signal") and data lines D1 -Dm for transmitting a data signal. The scan lines S1-Sn extend substantially in the row direction and are substantially parallel to each other, and the data lines D1-Dm extend substantially in the column direction and are substantially parallel to each other.

Each pixel includes a thin film transistor 10 connected to display signal lines S1 -Sn and D1 -Dm, a liquid crystal capacitor Cl, and a storage capacitor Cst connected thereto. The holding capacitor C _ST can be omitted as necessary.

The thin film transistor 10 is a three-terminal element whose control terminal and input terminal are connected to the scan line S1-Sn and the data line D1-Dm, respectively, and the output terminal is the liquid crystal capacitor Cl and the storage capacitor Cst. )

The liquid crystal capacitor Cl has a pixel electrode (not shown) and a common electrode (not shown) as two terminals, and the liquid crystal layer between the two electrodes functions as a dielectric. The pixel electrode is connected to the thin film transistor 10 and the common electrode 270 receives a common voltage Vcom.

The storage capacitor Cst is formed by overlapping a separate signal line (not shown) and the pixel electrode, and a predetermined voltage such as the common voltage Vcom is applied to the separate signal line.

In FIG. 2, when the scan signal is applied to the scan line Si and the thin film transistor 10 is turned on, the data voltage Vd supplied to the data line is applied to each pixel electrode through the thin film transistor 10. Then, an electric field corresponding to the difference between the pixel voltage Vp and the common voltage Vcom applied to the pixel electrode is applied to the liquid crystal (equivalently represented by the liquid crystal capacitor in FIG. 2), and thus transmittance corresponding to the intensity of the electric field. To allow light to pass through. At this time, the pixel voltage Vp should be maintained for one frame or one field, and the storage capacitor Cst is used to maintain the pixel voltage Vp applied to the pixel electrode.

Referring back to FIG. 1, the gate driver 200 sequentially applies a scan signal to the scan lines S1 -Sn, thereby turning on the thin film transistor having the gate electrode connected to the scan line to which the scan signal is applied.

The gray voltage generator 400 generates a gray voltage having a magnitude corresponding to gray data and supplies it to the data driver 300. The data driver 300 applies the gray voltage output by the gray voltage generator 400 to the corresponding data line.

The timing controller 600 is an input control signal for controlling the RGB image signals R, G and B and their display from an external graphic controller (not shown), for example, a vertical synchronization signal Vsync and a horizontal synchronization signal ( Hsync). The timing controller 400 properly processes the image signals R, G and B based on the input image signals R, G and B and the input control signal in accordance with the operating conditions of the liquid crystal display panel 100, and controls the gate control signals. After generating Sg, the data control signal Sd, the light source control signal Sb, and the like, the gate control signal Sg is sent to the gate driver 200 and the data control signal Sd is sent to the data driver 300. The processed image signals R, G, and B DATA are sent to the gray voltage generator 500 and the light source control signal Sb is sent to the light source controller 700.

The light emitting diodes 600a, 600b, and 600c respectively output light corresponding to R, G, and B to the liquid crystal display panel 100, and the light source controller 700 determines when the light emitting diodes 600a, 600b, and 600c are turned on. To control. In this case, according to an exemplary embodiment of the present invention, the timing controller 500 may be configured to supply the grayscale data from the data driver 300 to the data line and to turn on the R, G, and B light emitting diodes by the light source controller 700. It can be synchronized by the control signal provided by.

Next, the display operation of the liquid crystal display will be described in more detail with reference to FIG. 3.

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

As shown in FIG. 3, the liquid crystal display according to the exemplary embodiment of the present invention displays an image by dividing one frame into three fields, that is, an R field, a G field, and a B field. The driving frequency of one frame is 60 Hz, and each field performs display operation in synchronization with 180 Hz. Here, G1, G2, ..., Gn represent scan signals applied to the respective gate lines, and Cr, Cg, Cb are lit to instruct lighting of the R, G, and B light emitting diodes 600a, 600b, and 600c. It shows a signal.

One frame of R, G, and B image data supplied from the outside are separated into one frame of R image data, G image data, and B image data by the timing controller 400 in accordance with the display operation of the liquid crystal display device. The data is converted to the frame memory and stored in a frame memory (not shown). The stored image data of each color is read out of the R image data in an R field period of 1/180 seconds obtained by dividing one frame into three parts according to the read signal from the timing controller 400, and subsequently G image data is stored in the G field. Subsequently, B image data is sequentially read into the B field.

In the R field, the R image data voltage is sequentially written to all the pixels according to the scan signals G1, G2, ..., Gn, and then the light emitting diode 600a lights up in accordance with the lighting signal Cr in the illumination period. The R image is displayed on the liquid crystal display panel 100.

The G image data voltage is sequentially written to all the pixels according to the scan signals G1, G2, ..., Gn in the writing section of the G field, and then the light emitting diode 600b lights up in accordance with the lighting signal Cg in the lighting section. The G image is displayed on the liquid crystal display panel 100.

The B image data voltage is sequentially written to all the pixels according to the scan signals G1, G2, ..., Gn in the writing section of the B field, and then the light emitting diode 600c lights up in accordance with the lighting signal Cb in the lighting section. The B image is displayed on the liquid crystal display panel 100.

In this way, the image corresponding to each color component of R, G, and B is sequentially displayed for each field of each color of the R, G, and B fields so that the image of the R, G, and B color components is a visual afterimage of human. Is synthesized and visually recognized as a color image of one frame.

In FIG. 3, each field is divided into a writing period and an illumination period to display an image. However, the present invention is not limited thereto, and a reset period for erasing the data voltage applied in the previous field may be separately included.

Next, an operation of removing an afterimage when the power is turned off in the liquid crystal display according to the exemplary embodiment of the present invention will be described with reference to FIG. 4.

4 is a schematic diagram of a liquid crystal display according to another exemplary embodiment of the present invention.

As shown in FIG. 4, the liquid crystal display includes a timing controller 400, a power generator 800, a gate driver 200, and a liquid crystal display panel 100.

The power generator 800 receives an input voltage Vin from the outside to generate a driving voltage for driving the liquid crystal display, and the gate driver 200 according to the power enable signal PWEN from the timing controller 400. Apply the output voltage (Vout) to. The gate driver 200 receives the output voltage Vout and applies the output voltage Vout 'to the liquid crystal display panel 100.

When the power enable signal PWEN is at a high level, the power generator 800 applies the output voltage Vout to the gate driver 200, and when it is at a low level, the output voltage Vout. ).

When the power enable signal PWEN is set to active high as described above, the power enable signal PWEN remains at a low level even when power applied to the timing controller 400 is unexpectedly shut off and thus cannot operate. The power generator 800 prevents the output voltage Vout from being applied to the gate driver 200. As a result, the output voltage Vout 'of the gate driver 200 is also quickly removed, and thus the voltage charged in the capacitor and the liquid crystal display panel 100 at the final output terminal of the gate driver 200 may be quickly discharged. As a result, the afterimage of the liquid crystal display disappears quickly.

Although the power enable signal PWEN has been described as being applied to the power generator 800 from the timing controller 400, the present invention is not limited thereto and may be applied to the power generator 800 through the data driver 300. have. In some cases, the timing controller 400 and the data driver 300 may be formed of one chip, a so-called one chip. In this case, the power generator 800 may be generated by generating a power enable signal PWEN from the one chip. May be applied to.

Although the above has been described with reference to embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. It will be appreciated.

As described above, according to the exemplary embodiment of the present invention, the power enable signal is made active high to quickly remove the output voltage of the gate driver, thereby quickly removing the afterimage.

Claims (6)

And a plurality of scan lines for transmitting a scan signal, a plurality of data lines insulated from and intersecting the scan lines, and a plurality of pixels formed in an area surrounded by the scan lines and data lines, respectively, and connected to the scan lines and data lines. Liquid crystal display panel, A gate driver for sequentially supplying scan signals to the scan lines; A gray voltage generator for generating gray voltage corresponding to gray data; A data driver for supplying a gray voltage output from the gray voltage generator to a corresponding data line; A timing controller which transmits the gray data to the gray voltage generator, and controls the gate driver and the data driver; A power generation unit generating a driving voltage for driving the gate driver and applying the driving voltage to the gate driver according to a power enable signal; Including; The power generation unit applies the driving voltage to the gate driver when the power enable signal is at a high level, and blocks the driving voltage when the power level is low. And the power enable signal is changed to the low level when the power is cut off in a state where the power enable signal is set to the high level during normal operation. In claim 1, The power enable signal is transmitted from the timing controller to the power generator. In claim 1, The power enable signal is transmitted from the data driver to the power generator. The method according to any one of claims 1 to 3, Further comprising a plurality of light sources for outputting red, green, and blue light to the pixel, respectively, And each of the light sources is sequentially turned on. A driving method of a liquid crystal display device comprising a liquid crystal display panel, a gate driver applying a scan signal to the liquid crystal display panel, and a power generation unit applying a driving voltage to the gate driver. Applying a power enable signal to the power generation unit, and Applying the driving voltage to the gate driver according to the power enable signal Including; The driving voltage is applied when the power enable signal is at a high level, and the driving voltage is blocked when a low level is provided. The power enable signal is changed to the low level when the power is cut off in a state where the power enable signal is set to the high level during normal operation. In claim 5, And sequentially lighting red, green, and blue light sources on the liquid crystal display panel.

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