KR100956344B1 - Liquid crystal display - Google Patents

Abstract

The present invention relates to a liquid crystal display device capable of improving visibility and response speed according to a state of a screen.

According to an exemplary embodiment of the present invention, a liquid crystal display includes a plurality of pixels, a signal controller detecting a state of an image signal from an external source, and outputting a result thereof, a reference voltage generator configured to output two sets of reference voltages, and the reference voltage generator A data driver configured to generate a plurality of gray voltages based on the reference voltages from the pixels, and apply a gray voltage corresponding to the video signal among the generated gray voltages to the pixel as a data voltage, wherein the signal controller The number of pixels representing the first gray scale among the gray scale distributions of the signal is divided into a case over a predetermined range and a case below, and a control signal according to the result is output, and the reference voltage generator outputs a reference voltage according to the control signal. In this way, the visibility and the response speed can be improved simultaneously by adjusting the white gray voltage or the black gray voltage by dividing the white gray or the black gray into more than a predetermined range and the following.

Visibility, response speed, liquid crystal display, signal controller, data driver, gradation, white, black, amplifier

Description

Liquid crystal display {LIQUID CRYSTAL DISPLAY}

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 block diagram of a signal controller according to an embodiment of the present invention.

4 is a circuit diagram of a reference voltage generator according to an 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 more particularly, to a liquid crystal display device capable of improving response speed and visibility by changing a gray scale voltage according to a screen state.

A general liquid crystal display device includes two display panels and a liquid crystal layer having dielectric anisotropy interposed therebetween. An electric field is applied to the liquid crystal layer, and the intensity of the electric field is adjusted to adjust the transmittance of light passing through the liquid crystal layer to obtain a desired image. Such liquid crystal displays are typical of portable flat panel displays (FPDs), and among them, TFT-LCD using a thin film transistor (TFT) as a switching element is mainly used.

The LCD includes a pixel including a switching element, a data driver for applying a corresponding data voltage to the pixel, and a reference voltage generator for generating a reference voltage and supplying the reference voltage to the pixel.

The reference voltage generator generates a gray voltage of positive and negative polarity for inversion driving, and the data driver selects a gray voltage corresponding to an image signal among a plurality of gray voltages and applies it to the pixel as a data voltage.

At this time, a method of supplying a gray voltage includes a method of generating all necessary gray voltages in advance and supplying them to the data driver, and supplying some gray voltages as a reference, and dividing the rest within the data driver IC. Recently, as the number of bits of data increases, the number of gradation voltages to be expressed also increases, and usually the latter method is employed.

For example, in the latter method, in case of 6-bit data, all of the gray scale voltages required are 64 gray scale voltages, of which eight are referred to as reference voltages (hereinafter referred to as "reference voltages"). The values in between are generated by a certain rule in the IC of the data driver.

What is needed to obtain such a constant rule is gamma correction, which is to correct the light transmittance of the liquid crystal so that it is intended to obtain uniform light transmission characteristics. In addition, a kind of curve used for gamma correction is called a gamma curve.

On the other hand, for example, when setting the white gradation voltage in a normally white LCD, to reduce the contrast ratio and the response speed to set the gamma curve, or to some extent, give up the accuracy of the gamma curve to some extent. And aim for contrast ratio and response speed. To do this, the white voltage is applied separately from the rest of the data driver IC to secure the contrast ratio and the response speed, while maintaining the gamma curve.

In this case, when the white gray voltage is set using a separate resistor string, the lower the white gray voltage is, the faster the response speed is, but the visibility between grays is a problem. For example, when the total grayscale is 63 gray scales from 0 gray scales, there is a big difference between 63 gray scales and 62 gray scales, and the white part becomes prominent, causing problems in visibility. It is also more severe when viewed from the side.

Accordingly, an object of the present invention is to provide a liquid crystal display device which can improve response speed and visibility at the same time.

According to an exemplary embodiment of the present invention, a liquid crystal display including a plurality of pixels includes a signal controller, a reference voltage generator, and a data driver, and the signal controller controls the state of an image signal from the outside. Detect and output a result, wherein the reference voltage generator outputs a plurality of reference voltages, and the data driver generates a plurality of gray voltages based on the reference voltages from the reference voltage generator. The gray voltage corresponding to the video signal among the gray voltages is applied to the pixel as a data voltage. In addition, the signal controller divides the number of pixels representing the first gray scale among the gray scale distribution of the image signal into a case where the number of pixels is greater than or equal to a predetermined range and outputs a control signal according to the result, and the reference voltage generator is configured to output the control signal. Output the reference voltage accordingly. In this case, the signal controller may include a memory for storing the video signal from the outside, a detector for detecting a gray scale distribution of the video signal from the memory, and outputting a result thereof, and first and second according to the result of the detector. It is preferable to include a signal generator for generating the control signal having a state.

The reference voltage generator includes a resistor string in which a plurality of amplifiers and a plurality of resistors are connected in series, and the amplifier receives and integrates the control signal;

A second amplifier inverting the output from the first amplifier, a third amplifier amplifying the output from the second amplifier by one or more times, and a center voltage connected between the output of the third amplifier and the center of the resistor string; It is preferable to include a fourth amplifier for amplifying and outputting the difference of. Here, it is preferable that the value of the voltage corresponding to the first gray scale varies depending on the first and second states of the control signal.

On the other hand, the voltage corresponding to the first grayscale includes positive polarity and negative polarity, the output of the third amplifier is connected to the first grayscale voltage of the negative polarity, and the output of the fourth amplifier is the positive polarity zero. It may be connected to one gray voltage. In this case, the liquid crystal display may be a liquid crystal display device of normally white or normally black.

DETAILED DESCRIPTION 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.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like parts are designated by like reference numerals throughout the specification. When a portion of a layer, film, region, plate, etc. is said to be "on top" of another part, this includes not only when the other part is "right on" but also another part in the middle. On the contrary, when a part is "just above" another part, there is no other part in the middle.

A liquid crystal display according to an exemplary embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

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

As shown in FIG. 1, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal panel assembly 300, a gate driver 400, a data driver 500, and a data driver And a reference voltage generator 800 connected to 500 and a signal controller 600 for controlling them.                     

The liquid crystal panel assembly 300 includes a plurality of display signal lines G ₁ -G _n , D ₁ -D _m and a plurality of pixels connected to the plurality of display signal lines G ₁ -G _n , D ₁ -D _m , and arranged in a substantially matrix form. .

The display signal lines G ₁ -G _n and D ₁ -D _m are a plurality of gate lines G ₁ -G _n for transmitting a gate signal (also called a “scan signal”) and a data signal line or data for transmitting a data signal. Line D ₁ -D _m . The gate lines G ₁ -G _n extend substantially in the row direction and are substantially parallel to each other, and the data lines D ₁ -D _m extend substantially in the column direction and are substantially parallel to each other.

Each pixel includes a switching element Q connected to a display signal line G ₁ -G _n , D ₁ -D _m , and a liquid crystal capacitor C _LC and a storage capacitor C _ST connected thereto. It includes. The holding capacitor C _ST can be omitted as necessary.

The switching element Q is provided on the lower panel 100, and the control terminal and the input terminal are connected to the gate line G ₁ -G _n and the data line D ₁ -D _m, respectively. The output terminal is connected to the liquid crystal capacitor C _LC and the storage capacitor C _ST .

The liquid crystal capacitor C _LC has two terminals, the pixel electrode 190 of the lower panel 100 and the common electrode 270 of the upper panel 200, and the liquid crystal layer 3 between the two electrodes 190 and 270. Functions as a genetic material The pixel electrode 190 is connected to the switching element Q, and the common electrode 270 is formed on the front surface of the upper panel 200 and receives a common voltage V _com . Unlike in FIG. 2, the common electrode 270 may be provided in the lower panel 100. In this case, both electrodes 190 and 270 may be linear or rod-shaped.

The storage capacitor C _ST is formed by overlapping a separate signal line (not shown) and the pixel electrode 190 provided on the lower panel 100, and a predetermined voltage such as a common voltage V _com is applied to the separate signal line. Is approved. However, the storage capacitor C _ST may be formed such that the pixel electrode 190 overlaps the front end gate line directly above the insulator.

Meanwhile, in order to implement color display, each pixel must display color, which is possible by providing a red, green, or blue color filter 230 in a region corresponding to the pixel electrode 190. In FIG. 2, the color filter 230 is formed in a corresponding region of the upper panel 200. Alternatively, the color filter 230 may be formed above or below the pixel electrode 190 of the lower panel 100.

A polarizer (not shown) for polarizing light is attached to an outer surface of at least one of the two display panels 100 and 200 of the liquid crystal panel assembly 300.

The reference voltage generator 800 generates two sets of gradation voltages related to the transmittance of the pixel. One of the two sets has a positive value for the common voltage (V _com ) and the other set has a negative value.

The gate driver 400 is connected to the gate lines G ₁ -G _n of the liquid crystal panel assembly 300 to receive a gate signal formed by a combination of a gate on voltage V _on and a gate off voltage V _off from the outside. It is applied to the gate lines G ₁ -G _n .

The data driver 500 is connected to the data lines D ₁ -D _m of the liquid crystal panel assembly 300 to select the gray voltage from the reference voltage generator 800 and apply the gray voltage to the pixel as a data signal. It consists of a circuit.

The signal controller 600 generates control signals for controlling operations of the gate driver 400 and the data driver 500, and provides the corresponding control signals to the gate driver 400 and the data driver 500.

Next, the display operation of the liquid crystal display will be described in more detail.

The signal controller 600 inputs 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 sync signal V _sync and a horizontal sync signal. (H _sync ), a main clock (MCLK), a data enable signal (DE) is provided. The signal controller 600 generates a gate control signal CONT1 and a data control signal CONT2 based on the input control signal, and adjusts the image signals R, G, and B to match the operating conditions of the liquid crystal panel assembly 300. After appropriately processing, the gate control signal CONT1 is sent to the gate driver 400, and the data control signal CONT2 and the processed image signals R ', G', and B 'are sent to the data driver 500. In addition, the gray scale distribution state of the image signals R, G, and B is detected, and a dimming signal Sdim is output to the reference voltage generator 800 according to the result. This will be described later in detail.

The gate control signal CONT1 includes a vertical synchronization start signal STV indicating the start of output of the gate on pulse (gate on voltage section), a gate clock signal CPV for controlling the output timing of the gate on pulse, and a gate on pulse. An output enable signal OE or the like that defines a width.

The data control signal CONT2 is a load for applying a corresponding data voltage to the horizontal synchronization start signal STH indicating the start of input of the image data R ', G', and B 'and the data lines D ₁ -D _m . Signal LOAD, inverted signal RVS and data that inverts the polarity of the data voltage with respect to common voltage V _com (hereinafter referred to as " polarity of data voltage " by reducing " polarity of data voltage with respect to common voltage "). Clock signal HCLK and the like.

The data driver 500 sequentially receives image data R ′, G ′, and B ′ corresponding to one row of pixels in accordance with the data control signal CONT2 from the signal controller 600, and generates a reference voltage generator ( The image data R ', G', B 'is converted into the corresponding data voltage by selecting the gray voltage corresponding to each of the image data R', G ', and B' among the gray voltages from the 800.

The gate driver 400 applies the gate-on voltage V _on to the gate lines G ₁ -G _n in response to the gate control signal CONT1 from the signal controller 600, thereby applying the gate lines G ₁ -G _n. Turn on the switching element (Q) connected to.

The gate-on voltage V _on is applied to one gate line G ₁ -G _n so that a row of switching elements Q connected thereto is turned on (this period is "1H" or "1 horizontal period). (horizontal period) "and equal to one period of the horizontal sync signal Hsync, the data enable signal DE, and the gate clock CPV], and the data driver 500 converts each data voltage to a corresponding data line D. ₁ -D _m ). The data voltage supplied to the data lines D ₁ -D _m is applied to the corresponding pixel through the turned-on switching element Q.

The liquid crystal molecules change their arrangement according to the electric field generated by the pixel electrode 190 and the common electrode 270, and thus the polarization of light passing through the liquid crystal layer 3 changes. The change in polarization is represented by a change in transmittance of light by a polarizer (not shown) attached to the display panels 100 and 200.

In this manner, the gate-on voltages V _{on are} sequentially applied to all the gate lines G ₁ -G _n during one frame to apply data voltages to all the pixels. At the end of one frame, the next frame starts and the state of the inversion signal RVS applied to the data driver 500 is controlled so that the polarity of the data voltage applied to each pixel is opposite to that of the previous frame ("frame inversion). "). In this case, the polarity of the data voltage flowing through one data line may be changed (“line inversion”) within one frame or the polarity of the data voltage applied to one pixel row may be different according to the characteristics of the inversion signal RVS ( "Dot reversal").

Meanwhile, as described above, the signal controller 600 outputs a dimming signal Sdim according to the gradation distribution state of the image signals R, G, and B, and the reference voltage generator 800 outputs the dimming signal Sdim. The corrected white voltage is generated based on the following description, which will be described in detail with reference to FIGS. 3 and 4.

3 is a block diagram of a signal controller 600 according to an embodiment of the present invention, and FIG. 4 is a circuit diagram of a reference voltage generator 800 according to an embodiment of the present invention.

Hereinafter, a normal white liquid crystal display will be described as an example, and the same applies to a normally black liquid crystal display.

As shown in FIG. 3, the signal controller 600 according to an exemplary embodiment of the present invention includes a memory 601, a data detector 602, a dimming signal generator 603, and a data processor 604. Here, since the data processing unit 604 is the same as a normal data processing unit, description thereof will be omitted.

The memory 601 stores the video signals R, G, and B from the outside in one frame unit and supplies them to the data detector 602.

The data detector 602 detects the degree of distribution of the white gray levels in the image data R, G, and B corresponding to one frame.

For example, in the case of SXGA resolution, the total number of pixels is 1280 × 1024, and the white gradation appears when all of the red, green, and blue subpixels are all 63 gradations, so the ratio of the pixels representing the white gradations to the total number of pixels occupies. Is detected and the result is supplied to the dimming signal generator 603. For example, 1 and 0 are respectively outputted by dividing the pixel of the white gray level into the case of 30% or more of the whole and the case of 30% or less.

The dimming signal generator 603 outputs a high or low signal based on the control signal from the data detector 602. In the above example, when the pixel of the white gradation is 30% or more, low is output, and when it is 30% or less, high is output.

The reference voltage generator 800 outputs a white gray voltage based on the dimming signal Sdim from the dimming signal generator 603.

The reference voltage generator 800 includes amplifiers OP1, OP2, OP3, and OP4 and a resistor string.

First, the resistor string includes a plurality of resistors R11 to R26 connected in series between the power supply AVDD and ground, and outputs a positive reference voltage on the upper side and a negative side on the basis of the center voltage VCNT. Output the reference voltage of polarity. The positive and negative white gray voltages VG7 and VG8 are output at the node closest to the center voltage VCNT.

In addition, as described above, although a plurality of gray voltages are generated from a resistor string provided in the data driver 500 based on the reference voltage generated by the reference voltage generator 800, the white gray voltages VG7 and VG8 and the center voltage are generated. Since no resistance heat exists between the VCNTs, the white gray voltage generated by the reference voltage generator 800 is no longer separated and used in the data driver 500 as it is.

The amplifier OP1 includes a non-inverting terminal grounded as an integrator and an inverting terminal connected between the resistor R1 and the capacitor C1, and receives and integrates a dimming signal Sdim.                     

The amplifier OP2 includes a non-inverting terminal grounded as an inverting amplifier and an inverting terminal connected between the resistors R3 and R4, and inverts the output from the amplifier OP1. This is to make it positive because the output of the amplifier OP1 has a negative polarity.

The amplifier OP3 is a non-inverting amplifier. The amplifier OP3 includes a non-inverting terminal connected to the output of the amplifier OP2 and an inverting terminal connected between the resistors R5 and R6. The output of the amplifier OP2 is 1 times. The amplification is then performed and supplied to the negative white gray voltage VG8.

The amplifier OP4 is a differential amplifier, and includes a non-inverting terminal connected to the center voltage VCNT and an inverting terminal connected between the resistors R8 and R9 and the center voltage VCNT and the amplifier OP3. The difference of the output voltage is amplified and supplied to the positive white gray voltage VG7.

Table 1 shows the relationship between the white gradation voltage and the response speed. Tr represents the rising time of the liquid crystal molecules, Tf represents the falling time and T _total represents the total time.

As shown in Table 1, the lower the white voltage, the faster the response speed, while the visibility problem occurs, and the higher the response, the slower the response speed, but the visibility problem is reduced.

Accordingly, in the above-described example, when the pixel representing the white gray level is 30% or more of all pixels, the dimming signal Sdim is set to 0.7 V so as to input low to improve the visibility of the screen. On the contrary, if it is less than 30% of the total, the white gray voltage is set to, for example, 0.1V to improve the response speed by inputting high.

In the embodiment of the present invention, the value corresponding to the row of the dimming signal Sdim is set to 0V. Therefore, since there is no input voltage value, the reference voltage generator 800 outputs the same without changing the reference voltage value. At this time, the values of the resistor strings R11 to R26 are set so that the value of the output white gray voltage is 0.7V. In addition, by applying a predetermined voltage corresponding to the high of the dimming signal Sdim, the values of the respective resistors R1 to R10 and the capacitor C1 are adjusted so that the value of the finally output white gray voltage is 0.1V.

Although an embodiment of the present invention has been described with respect to a normally white liquid crystal display, it will be appreciated that the present invention can be applied to a normally black liquid crystal display.

In this way, by detecting the state of the input image data and setting the white gradation voltage to improve the visibility when the pixel representing the white gradation is over a certain range and to improve the response speed when the pixel is less than the predetermined range, the response speed and visibility Can be improved at the same time.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

Claims (9)

A liquid crystal display device comprising a plurality of pixels, A signal controller which detects a state of an image signal from the outside and outputs a result thereof; A reference voltage generator for outputting two sets of multiple reference voltages, and A data driver which generates a plurality of gray voltages based on the reference voltages from the reference voltage generator, and applies a gray voltage corresponding to the image signal among the generated gray voltages to the pixel as a data voltage; Including, The signal controller outputs a control signal according to the result by dividing the number of pixels representing the first gray scale among the gray scale distribution of the video signal to be greater than or equal to a predetermined range and less than or equal to a predetermined range, The reference voltage generator outputs a reference voltage according to the control signal. Liquid crystal display. In claim 1, The signal controller A memory for storing the video signal from the outside; A detector which detects the gradation distribution of the video signal from the memory and outputs the result; and A signal generator configured to generate the control signals having first and second states according to a result of the detector Containing Liquid crystal display. In claim 2, The reference voltage generator includes a resistor string in which a plurality of amplifiers and a plurality of resistors are connected in series. The amplifier A first amplifier receiving and integrating the control signal, A second amplifier inverting the output from the first amplifier, A third amplifier for amplifying the output from the second amplifier by one or more times, and And a fourth amplifier for amplifying and outputting a difference between the output of the third amplifier and the center voltage connected to the center of the resistor string. Liquid crystal display. The method of claim 2 or 3, The value of the reference voltage corresponding to the first grayscale varies in accordance with first and second states of the control signal. 4. The method of claim 3, The first gray level reference voltage, which is a reference voltage corresponding to the first gray level, is positive and negative. Including polarity, An output of the third amplifier is connected to the first gradation reference voltage of the negative polarity, An output of the fourth amplifier is connected to the first gray reference voltage of the positive polarity. Liquid crystal display. In claim 1, The liquid crystal display device is normally white. In claim 1, The liquid crystal display device is a normally black liquid crystal display device. In claim 1, When the reference voltage corresponding to the first grayscale is a first grayscale reference voltage, The reference voltage generator sets the first gray reference voltage according to the control signal. Liquid crystal display. In claim 8, When the number of pixels representing the first gray scale is greater than or equal to the predetermined range, the The first gray scale reference voltage is set to lower the luminance represented by the first gray scale, If the number of pixels representing the first gray scale is smaller than the predetermined range, The first gray scale reference voltage is set to increase the luminance represented by the first gray scale. Liquid crystal display.

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