KR100612337B1 - Thin Film Transistor Liquid Crystal Display and Driving method threrof - Google Patents

Abstract

The present invention relates to a liquid crystal display and a driving method thereof.

According to the present invention, red, green, and blue light is sequentially transmitted to one of a plurality of pixels, and the driving method includes a red field, a blue field, and a green field for driving red, blue, and green light, respectively. In each of the red field, green field, and blue field, a first period for applying a constant voltage higher than the first driving voltage, and the second common voltage is constant compared to the second driving voltage for each of the red field, the green field, and the blue field. Drive to the second section to apply a low voltage. In this way, even if the gray level is changed in units of frames, a voltage difference does not occur regardless of the Vcom code, and thus no flicker occurs.

LCD, Drive, FRM, Invert

Description

Thin film transistor liquid crystal display and driving method thereof {Thin Film Transistor Liquid Crystal Display and Driving method threrof}

1 is a view showing a pixel of a conventional TFT-LCD.

2 is a waveform diagram illustrating a driving method of a conventional analog liquid crystal display device.

3 is a waveform diagram illustrating a driving method of a conventional digital liquid crystal display device.

4 is a waveform diagram showing a conventional FRM driving method.

5 is a diagram illustrating a liquid crystal display device according to an exemplary embodiment of the present invention.

6 illustrates driving waveforms of the liquid crystal display according to the exemplary embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor liquid crystal display device and a driving method thereof, and more particularly, to a thin film transistor liquid crystal display device of 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. Panel-type displays are being developed.

An LCD 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 to the substrate from an external light source (backlight). A display device for obtaining an image signal.

Such LCDs are typical of portable flat panel displays, and among them, TFT-LCD using a thin film transistor (TFT) as a switching element is mainly used.

In the TFT-LCD, each pixel may be modeled as a capacitor having a liquid crystal as a dielectric, that is, a liquid crystal capacitor. The equivalent circuit of each pixel in the LCD is shown in FIG.

As shown in FIG. 1, each pixel of the liquid crystal display includes a TFT 10 having a source electrode and a gate electrode connected to the data line Dm and the scan line Sn, respectively, a drain electrode of the TFT, and a common voltage Vcom. It includes a liquid crystal capacitor (Cl) connected between and a storage capacitor (Cst) connected to the drain electrode of the TFT.

In Fig. 1, when the scan signal is applied to the scan line Sn and the TFT 10 is turned on, the data voltage Vd supplied to the data line is applied to each pixel electrode (not shown) through the TFT. 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. 1), 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. In FIG. 1, the storage capacitor Cst is used to maintain the pixel voltage Vp applied to the pixel electrode.

In general, the liquid crystal display may be divided 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 composed of three primary colors of red (R), green (G), and blue (B) on one of two substrates, and transmits the amount transmitted through the color filter layer. Display the desired color by adjusting. 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 to transmit light emitted from a single light source to the R, G, and B color filter layers. Thereby displaying the desired color.

As described above, in a liquid crystal display device displaying a color 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, there is a manufacturing problem that a separate color filter layer must be formed on the liquid crystal display substrate, and there is a problem that the light transmittance of the color filter itself must be improved.

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 synchronism with the lighting cycle to display a full color image. Get it. 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 to one pixel without dividing one pixel into R, G, and B unit pixels. The color image is displayed by using the afterimage effect of the eye by time-divisionally displaying the light of?.

The field sequential driving method can 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, thereby applying the applied gray voltage. Gradation display is performed with the amount of transmitted light corresponding to.

2 is a diagram illustrating a driving voltage and a transmitted light amount according to a conventional LCD driving apparatus.

Referring to FIG. 2, in the R field section T1 for displaying the R color, a driving voltage of the V11 level is applied to the liquid crystal so that light corresponding to the driving voltage of the V11 level passes through the liquid crystal. In the G field section T2 for displaying the G color, a driving voltage of the V12 level is applied so that light corresponding to the driving voltage of the V12 level passes through the liquid crystal. Then, in the B field section T3 for displaying the B color, a driving voltage of the V13 level is applied to obtain a light transmittance corresponding to the driving voltage of the V13 level. The desired color image is displayed by the sum of the R, G, and B lights transmitted in the T1, T2, and T3 sections, respectively.

Referring to FIG. 2, the period in which the R color is actually displayed is a period Tr from the time t2 to t3 when the R backlight is emitted, and the G color is displayed in the period from the time t5 to t6 when the G backlight is emitted ( Tg), and the color B is displayed in the period Tb from the time t8 to t9 when the B backlight emits light.

On the other hand, the digital driving method makes the driving voltage applied to the liquid crystal constant and controls the voltage application time to perform gradation display. According to this digital driving method, the gray scale is displayed by adjusting the accumulated amount of light transmitted through the liquid crystal by keeping the driving voltage constant and controlling the voltage applied state and the voltage unapplied state in a timely manner.

FIG. 3 is a waveform diagram illustrating a conventional method for driving a liquid crystal display device of a digital driving method, and illustrates a waveform of a driving voltage according to driving data of a predetermined bit and a waveform of an amount of light passing through the liquid crystal. will be.

Referring to FIG. 3, grayscale waveform data corresponding to each grayscale is provided as a digital signal of a predetermined bit, for example, 7bit, and a grayscale waveform according to the 7bit data is applied to the liquid crystal. Then, the transmission amount of the liquid crystal is determined according to the applied gradation waveform to perform gradation display.

4 is a waveform diagram showing a conventional FRM driving method.

Referring to FIG. 4, in the related art, the common voltage applied to the common electrode in units of fields of R, G, and B is driven to be larger or smaller than the driving voltage, which is called field inversion driving. Here, Vcom (+) means a period in which the common voltage is larger than the driving voltage, and Vcom (-) means a period in which the common voltage is smaller than the driving voltage.

However, in the conventional FRM driving method, when the R field of the current frame and the R field of the next frame are driven with different gradations, the flicker is caused by the voltage difference caused by the change of Vcom (-) and Vcom (+). There is a disadvantage that such a phenomenon occurs.

SUMMARY OF THE INVENTION The present invention has been made in an effort to solve the disadvantages of the related art, and provides a thin film transistor liquid crystal display device and a driving method thereof in which inversion driving is performed in each of R, G, and B fields so that a voltage difference does not occur between fields. It is.

A method of driving a thin film transistor liquid crystal display device according to a feature of the present invention for achieving the above object is
A plurality of scan lines, a plurality of data lines insulated from and intersecting the scan lines, a plurality of pixels formed in an area surrounded by the scan lines and data lines, respectively surrounded by the scan lines and data lines, and arranged in a matrix; Each pixel includes a thin film transistor having a gate electrode and a source electrode connected to the scan line and a data line, and a pixel capacitor having one side connected to a drain electrode of the thin film transistor and the other side connected to a common electrode line. A method of driving a thin film transistor liquid crystal display device sequentially transmitting red, green, and blue light to one of the plurality of pixels,
The driving method includes a red field, a blue field, and a green field for driving red, blue, and green light, respectively.
For each of the red field, green field and blue field,
A first step of applying a first common voltage having a level lower than a driving voltage applied to the pixel through the thin film transistor from the data line in response to a scan signal applied to the scan line;
And applying a second common voltage having a level higher than a driving voltage applied to the pixel and having a predetermined magnitude.
On the other hand, the thin film transistor liquid crystal display device according to the characteristics of the present invention,
A plurality of scan lines for transmitting a scan signal, a plurality of data lines insulated from and intersect the scan lines, a thin film transistor and a thin film transistor connected to the scan line and the data line, respectively, in a region surrounded by the scan line and the data line. A liquid crystal display panel including a plurality of pixels arranged in a matrix form, the pixel capacitor including a pixel capacitor having one side connected to the common electrode and the other side connected to the common electrode;
A gate driver for sequentially supplying scan signals to the scan lines;
A gray voltage generator which generates a gray voltage corresponding to the gray;
A data driver for supplying a gray voltage output from the gray voltage generator to a corresponding data line;
In a red field, a green field, and a blue field having a first period and a second period, respectively, driving is applied to the pixel from the data line through the thin film transistor in response to a scan signal applied to the scan line during the first period. A first common voltage having a level lower than the voltage and having a constant magnitude is generated, and a second common voltage having a level higher than a driving voltage applied to the pixel and having a constant magnitude is generated and applied to the common electrode during the second period. A common voltage generator; And
And a light source sequentially outputting light of red, green, and blue in the red field, the green field, and the blue field, respectively.

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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.

5 illustrates a thin film transistor liquid crystal display according to an exemplary embodiment of the present invention.

As shown in FIG. 5, the liquid crystal display according to the exemplary embodiment of the present invention is

The liquid crystal display panel 100, the scan driver 200, the data driver 300, the gray voltage generator 400, the timing controller 500, the common voltage generator 600, and the R, G, and B light sources are respectively Output light emitting diodes 700a, 700b, 700c and a light source controller 800.

A plurality of scan lines (not shown) are formed in the liquid crystal display panel 100 to transmit a gate-on signal, and are insulated from and intersect with the plurality of scan lines to transmit gray data voltages and reset voltages corresponding to gray data. A data line (not shown) is formed for this purpose. A plurality of pixels arranged in a matrix form is surrounded by a scan line and a data line, and each pixel includes a thin film transistor (not shown) and a drain electrode of the thin film transistor, in which a gate electrode and a source electrode are connected to the scan line and the data line, respectively. One side is connected to the other side, and the other side includes a pixel capacitor (not shown) and a storage capacitor (not shown) connected to the common electrode.

The gate driver 200 sequentially applies a scan signal to the scan line to turn on the thin film transistor to which the scan signal is applied, so that the data voltage applied to the data line is transferred to the pixel electrode through the thin film transistor.

The timing controller 500 receives the gray level data signals R, G, and B data, the horizontal sync signal Hsync, and the vertical sync signal Vsync from an external or graphic controller (not shown), and then requires a control signal Sg. , Sd, Sb are supplied to the scan driver 200, the data driver 300, and the light source controller 800, and the grayscale data R, G, and B DATA are supplied to the grayscale voltage generator 400.

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 common voltage generator 600 applies the common voltage to the common electrode while converting the level of the common voltage each time the period is changed. That is, the first common voltage is generated in the first period of each field, and the second common voltage is generated and supplied to the common electrode in the second period.

Here, the difference between the first common voltage and the driving voltage level and the difference between the second common voltage and the driving voltage level are equal in magnitude and opposite in polarity.

The light emitting diodes 700a, 700b, and 700c respectively output light corresponding to R, G, and B to the LCD panel, and the light source controller 800 controls the lighting timing of the light emitting diodes 700a, 700b, and 700c. 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 800. It can be synchronized by the control signal provided by.

6 illustrates a driving waveform of a thin film transistor liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 6, when the Vcom inversion driving is performed in the field sequential driving type thin film transistor liquid crystal display, each field of the red field, the green field, and the blue field is divided into two sections to be inverted.

In the first section, the driving voltage Vd1 is made smaller than the common voltage Vcom (+), and in the second section, the driving voltage Vd2 is made larger than the common voltage Vcom (−).

In Fig. 6, the levels of the driving voltage Vd1 and the driving voltage Vd2 are different but may be the same.

According to the embodiment of the present invention, even if the gray level is changed in units of frames because Vcom (+) and Vcom (-) exist in the same R, G, and B fields, the voltage does not occur regardless of the Vcom code. Flicker does not occur.

In this embodiment of the present invention, one field is divided into two to invert driving, but if necessary, the driving may be divided into four, eight, or more periods.

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 present invention, even if the gray level is changed in units of frames, the voltage does not occur regardless of the Vcom code, and thus no flicker occurs.

Claims (6)

A plurality of scan lines, a plurality of data lines insulated from and intersecting the scan lines, a plurality of pixels formed in an area surrounded by the scan lines and data lines, respectively surrounded by the scan lines and data lines, and arranged in a matrix; Each pixel includes a thin film transistor having a gate electrode and a source electrode connected to the scan line and a data line, and a pixel capacitor having one side connected to a drain electrode of the thin film transistor and the other side connected to a common electrode line. A method of driving a thin film transistor liquid crystal display device sequentially transmitting red, green, and blue light to one of the plurality of pixels, The driving method includes a red field, a blue field, and a green field for driving red, blue, and green light, respectively. For each of the red field, green field and blue field, A first step of applying a first common voltage having a level lower than a driving voltage applied to the pixel through the thin film transistor from the data line in response to a scan signal applied to the scan line; And applying a second common voltage having a level higher than a driving voltage applied to the pixel and having a predetermined magnitude. The method of claim 1, And the absolute value of the difference between the first common voltage level and the driving voltage level is equal in magnitude and opposite in polarity to the second common voltage level and the driving voltage level. The method according to claim 1 or 2, And a third step of repeating the first step and the second step. A plurality of scan lines for transmitting a scan signal, a plurality of data lines insulated from and intersect the scan lines, a thin film transistor and a thin film transistor connected to the scan line and the data line, respectively, in a region surrounded by the scan line and the data line. A liquid crystal display panel including a plurality of pixels arranged in a matrix form, the pixel capacitor including a pixel capacitor having one side connected to the common electrode and the other side connected to the common electrode; A gate driver for sequentially supplying scan signals to the scan lines; A gray voltage generator which generates a gray voltage corresponding to the gray; A data driver for supplying a gray voltage output from the gray voltage generator to a corresponding data line; In a red field, a green field, and a blue field having a first period and a second period, respectively, driving is applied to the pixel from the data line through the thin film transistor in response to a scan signal applied to the scan line during the first period. A first common voltage having a level lower than the voltage and having a constant magnitude is generated, and a second common voltage having a level higher than a driving voltage applied to the pixel and having a constant magnitude is generated and applied to the common electrode during the second period. A common voltage generator; And And a light source sequentially outputting red, green, and blue light in the red, green, and blue fields, respectively. delete The method of claim 4, wherein The absolute value of the difference between the first common voltage level and the driving voltage level is equal to the absolute value of the difference between the second common voltage level and the driving voltage level, and the polarity is opposite.

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