KR100627307B1 - A liquid crystal display and a driving method thereof - Google Patents

Abstract

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

The present invention provides a method of driving a liquid crystal display device that sequentially transmits red, green, and blue light to one of a plurality of pixels, wherein the driving method includes the number of voltage levels equal to the number of digital bits when implementing 64 gradations. It is characterized in that the multiplied value is 2048 or more.

According to the present invention, in the case of the digital analog complex driving, the condition for determining the voltage level for implementing a constant gray level and the number of bits for implementing the gray level can be found, and the gray level can be accurately implemented according to such conditions.

Field sequential, FS, LCD, light source, LED, gradation

Description

Liquid crystal display device and driving method thereof. {A LIQUID CRYSTAL DISPLAY AND A DRIVING METHOD THEREOF}

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

5 shows an example of a digital analog method.

Fig. 6 is a diagram showing the tone when the number of digital bits is 10 bits and 11 bits in the digital driving method.

Fig. 7 is a diagram showing the gradation when the digital bit number and the voltage level number are set according to the conditions in the digital analog driving method.

The present invention relates to a liquid crystal display device and a driving method thereof, and more particularly, to a 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, and according to such demands, flat displays such as liquid crystal displays (LCDs) instead of cathode ray tubes (CRTs) are required. 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 are not divided into R, G, and B pixel units. By displaying the light sequentially in time division, a color image is displayed using the afterimage effect of the eye.

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 Tr 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 Tg 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 Tb 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 Tr, Tg, and Tb sections, respectively.

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.

On the other hand, research is being actively conducted to drive a liquid crystal display device by mixing a digital method and an analog method.

The technical problem to be achieved in the present invention is a liquid crystal display for finding a condition for determining the number of voltage levels for implementing a constant gradation and the number of bits for gradation in the case of a digital analog composite drive and implements gradation under such conditions; It is to provide a driving method thereof.

Method of driving a liquid crystal display device according to an aspect 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 data lines arranged in a matrix form having a switching element connected to the scan lines and the data lines, respectively; A driving method of a liquid crystal display device comprising a pixel and sequentially transmitting red, green, and blue light to one of the plurality of pixels.

The driving method is to display the gray scale in a digital analog composite,

When implementing 64 gradations, the value of multiplying the number of voltage levels by the number of digital bits is 2048 or more.

According to one aspect of the present invention,

A matrix form having a plurality of scan lines for transmitting a scan signal, a plurality of data lines insulated from and intersecting the scan lines, a switching element formed in an area surrounded by the scan lines and data lines, and connected to the scan lines and data lines, respectively. A liquid crystal display panel including a plurality of pixels arranged in a line;

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

A gray voltage generator which generates a gray voltage corresponding to gray data;

A data driver for supplying a gradation voltage output from the gradation voltage generator and a reset pulse for initializing the state of the liquid crystal to a specific state; And

It includes a light source to sequentially output the light of red, green, blue to one pixel,

When the gray voltage generator generates 64 gray levels, the value obtained by multiplying the number of voltage levels by the number of digital bits is 2048 or more.

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.

Next, a liquid crystal display according to an exemplary embodiment of the present invention will be described with reference to FIG. 4.

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

As shown in FIG. 4, the liquid crystal display according to the exemplary embodiment of the present invention includes a liquid crystal display panel 100, a scan driver 200, a data driver 300, a gray voltage generator 500, and a timing controller ( 400, light emitting diodes 600a, 600b, and 600c respectively outputting R, G, and B light sources, and a light source controller 700.

A plurality of scan lines are formed on the liquid crystal display panel 100 to transmit a gate-on signal, and the plurality of scan lines are insulated from and intersect with the plurality of scan lines, and the data lines are configured to transmit gray data voltages and reset voltages corresponding to gray data. It is formed. The plurality of pixels 110 arranged in a matrix form are surrounded by scan lines and data lines, respectively. Each pixel includes a thin film transistor (not shown) having a gate electrode and a source electrode connected to the scan line and a data line, a pixel capacitor (not shown), and a storage capacitor (not shown) connected to the drain electrode of the thin film transistor. do.

The gate driver 200 sequentially applies a scan signal to the scan line, thereby turning on the TFT to which the gate electrode is connected to the scan line to which the scan signal is applied.

The timing controller 400 receives the gray level data signals R, G, and B data, the horizontal synchronization signal Hsync, and the vertical synchronization signal Vsync from an external or graphic controller (not shown), and controls necessary signals Sg, Sd and Sb are supplied to the scan driver 200, the data driver 300, and the light source controller 700, respectively, and the gray scale data R, G, and B DATA are supplied to the gray voltage generator 500.

The gray voltage generator 500 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 500 to the data line in the gray bit period, and applies a reset voltage to the data line to reset the data in the reset period. do.

The light emitting diodes 600a, 600b, and 600c respectively output light corresponding to R, G, and B to the LCD panel 100 during the lighting period, and the light source controller 700 turns on the light emitting diodes 600a, 600b, and 600c. Control the timing.

In this case, the timing at which the gray level voltage is supplied or stopped from the data driver 300 to the data line and the timing at which the R, G, and B light emitting diodes are turned on by the light source controller 800 are controlled by the timing controller 500. Can be synchronized by a signal.

Here, the gray voltage generator generates a digital analog complex drive of the gray voltage corresponding to the gray level, and may express various gray levels according to the number of voltage levels and the number of digital bits. An example of such a digital analog composite drive is shown in FIG.

In the field sequential driving type liquid crystal display which is currently digitally driven to find the conditions for the number of voltage levels and the number of digital bits for the digital analog complex driving as shown in FIG. 5, the number of digital bits has 10 bits. The simulation was performed using and 11 bits. The results are shown in FIG.

Referring to FIG. 6, when the number of digital bits is 10 bits, errors in gradation and simulated gradation are severe, and the gradation does not change smoothly according to a certain rule.

However, when the number of digital bits is 11 bits, the calculated gray scale and the simulated gray scale value almost match.

That is, 10 bits (2 ¹⁰ = 1024), in this case 64 gray scale display incomplete

11 bits (2 ¹¹ = 2048), in which case 64 gradations can be displayed

It can be seen that.

From this, it can be seen that in order to express 64 gray levels, at least two voltage levels, the number of digital bits should be 11 or more.

Similarly, when applied to digital analog complex driving, the number of voltage levels multiplied by the number of digital bits must be greater than 2048 to achieve 64 gradations.

This is expressed as a formula as follows.

Here, the number of digital bits is n and the number of voltage levels is M.

In fact, the results of simulating the digital analog composite driving method with different voltage levels are shown in FIG.

Referring to Fig. 7, the gradation and the simulated gradation coincide with both the case where the number of digital bits is set to 16 levels and the case where the number of digital bits is set to 7 levels.

As described above, in order to implement 64 gray scales in the case of the digital analog complex driving, gray scales can be accurately implemented by appropriately determining the number of digital bits and the number of voltage levels according to the above conditions.

Although the embodiment of the present invention has been described with respect to 64 gradations, it can be applied to other gradation liquid crystal display devices as necessary.

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. I can understand that it can.

As described above, according to the present invention, when performing the digital analog composite drive, it is possible to predict the conditions for determining the number of voltage levels for implementing a constant gradation and the number of bits for gradation. The number of digital bits can be determined.

Claims (3)

A plurality of scan lines, a plurality of data lines insulated from and intersecting the scan lines, a plurality of data lines arranged in a matrix form having a switching element connected to the scan lines and the data lines, respectively; A driving method of a liquid crystal display device comprising a pixel and sequentially transmitting red, green, and blue light to one of the plurality of pixels. The driving method, And a voltage multiplied by the number of digital bits when the number of voltage levels is implemented to be 2048 or more. delete A matrix form having a plurality of scan lines for transmitting a scan signal, a plurality of data lines insulated from and intersecting the scan lines, a switching element formed in an area surrounded by the scan lines and data lines, and connected to the scan lines and data lines, respectively. A liquid crystal display panel including a plurality of pixels arranged in a line; A gate driver for sequentially supplying scan signals to the scan lines; A gray voltage generator which generates a gray voltage corresponding to gray data; A data driver for supplying a gradation voltage output from the gradation voltage generator and a reset pulse for initializing the state of the liquid crystal to a specific state; And It includes a light source to sequentially output the light of red, green, blue to one pixel, And when the gray voltage generator generates 64 gray levels, a value obtained by multiplying the number of voltage levels by the number of digital bits is 2048 or more.

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