KR20060018396A - Liquid crystal display - Google Patents

Abstract

The present invention relates to a liquid crystal display device.

According to an aspect of the present invention, a liquid crystal display device includes a liquid crystal panel assembly having a plurality of pixels and a switching element connected thereto, a gray voltage generator generating a plurality of gray voltages, and a gray level corresponding to an image signal among the gray voltages. A data driver which selects a voltage as a data voltage and applies it to the pixel; and a common voltage generator that generates a common voltage and applies it to the liquid crystal panel assembly, wherein the common voltage generator is provided to an operational amplifier and an output terminal of the operational amplifier. And first and second multi-switches that are connected.

In this manner, afterimage and flicker may be improved by subdividing and compensating the total resistance and the kickback voltage distributed in the display panel assembly.

LCD, Common Voltage, Resistance, Kickback Voltage, Multi Switch, Flicker, Afterimage

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 an example of a circuit diagram of a common voltage generator of a liquid crystal display according to an exemplary embodiment of the present invention.

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

The present invention relates to a liquid crystal display, and more particularly, to a common voltage generator of a liquid crystal display.

A typical liquid crystal display (LCD) includes two display panels provided with pixel electrodes and a common electrode, and a liquid crystal layer having dielectric anisotropy interposed therebetween. The pixel electrodes are arranged in a matrix and connected to switching elements such as thin film transistors (TFTs) to receive data voltages one by one in sequence. The common electrode is formed over the entire surface of the display panel and receives a common voltage. The pixel electrode, the common electrode, and the liquid crystal layer therebetween form a liquid crystal capacitor, and the liquid crystal capacitor becomes a basic unit that forms a pixel together with a switching element connected thereto.

In such a liquid crystal display, a voltage is applied to two electrodes to generate an electric field in 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. In this case, in order to prevent degradation caused by an electric field applied to the liquid crystal layer for a long time, the polarity of the data voltage with respect to the common voltage is inverted frame by frame, row by pixel, or pixel by pixel.

Such a liquid crystal display includes a liquid crystal panel assembly having a pixel including a switching element and a display signal line connected thereto, a data driver for applying a corresponding data voltage to the pixel through a switching element, and generating a gray voltage and supplying the gray voltage to the data driver. The gray voltage generator includes a common voltage generator that provides a common voltage to the liquid crystal panel assembly.

In such liquid crystal display devices, there is a constant resistance in the assembly and a kick-back voltage necessarily occurs due to the parasitic capacitance between the gate and drain of the switching element, which causes flicker or an afterimage on the screen. Etc.

In order to solve the problem of flicker or afterimage caused by such resistance or kickback voltage, some compensation is made by feeding back the common voltage applied to the assembly. However, the resistance or kickback voltage is not consistently present at the front of the assembly, but varies slightly depending on the position of the assembly, especially as the resolution increases and the larger the area becomes.

Current liquid crystal display devices have a limited resistance range and a range of kickback voltages and are compensated for them, and thus there is a limit in improving afterimage and flicker.

The technical problem to be achieved by the present invention is to provide a liquid crystal display device that can solve the problems of the prior art.

According to an aspect of the present invention, a liquid crystal panel assembly including a plurality of pixels and a switching element connected thereto, a gray voltage generator generating a plurality of gray voltages, and a gray level A data driver which selects a gray voltage corresponding to an image signal among the voltages as a data voltage and applies it to the pixel, and generates a common voltage and applies it to the liquid crystal panel assembly,

The common voltage generator includes an operational amplifier and first and second multi-switches connected to an output terminal of the operational amplifier.

In this case, the first multi-switch may be connected to an output terminal of the operational amplifier, and the second multi-switch may be connected to a center of a resistor string connected in series between the output terminal and a ground terminal. The second multi-switch may emit first to eighth corrected common voltages, respectively.

In addition, the liquid crystal panel assembly may include a plurality of short points, and the operational amplifier may receive a feedback voltage from at least one of the short points.

In addition, the data driver may include a plurality of data driver integrated circuits, and output voltages of the first and second multi-switches may be applied to the liquid crystal panel assembly through dummy channels of the data driver integrated circuit.

On the other hand, the operational amplifier may be a differential amplifier (differential amplifier).

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 part of a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the other part being "right over" 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.

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, 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 500 connected thereto. The gray voltage generator 800 connected to the signal generator 500 and a signal controller 600 for controlling the gray voltage generator 800 are included.

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 line D for transmitting a data signal. 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, such as a thin film transistor, is provided in the lower panel 100, and the control terminal and the input terminal are three-terminal elements, respectively, with gate lines G ₁ -G _n and data lines D ₁ -D _m . The output terminal is connected to a liquid crystal capacitor (C _LC ) and a holding 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. It functions as a dielectric. 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, at least one of the two electrodes 190 and 270 may be linear or rod-shaped.

The storage capacitor C _ST , which serves as an auxiliary part of the liquid crystal capacitor C _LC , is formed by overlapping a separate signal line (not shown) and the pixel electrode 190 provided on the lower panel 100 with an insulator interposed therebetween. A predetermined voltage such as the common voltage V _com is applied to this separate signal line. 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.

On the other hand, to implement color display, each pixel uniquely displays one of the three primary colors (spatial division) or each pixel alternately displays the three primary colors over time (time division) so that the desired color can be selected by the spatial and temporal sum of these three primary colors. To be recognized. 2 shows that each pixel includes a red, green, or blue color filter 230 in a region corresponding to the pixel electrode 190 as an example of spatial division. Unlike FIG. 2, 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 gray voltage generator 800 generates two sets of gray 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 and usually consists of a plurality of integrated circuits.

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 gray voltage generator 800 and apply the gray voltage to the pixel as a data signal. It consists of a circuit.

The plurality of gate driving integrated circuits or data driving integrated circuits may be mounted in a tape carrier package (TCP) (not shown) in the form of a chip to attach the TCP to the liquid crystal panel assembly 300, and may be advantageous without using TCP. These integrated circuit chips may be directly attached onto the substrate (chip on glass, COG mounting method), and a circuit performing the same functions as those integrated circuit chips may be directly formed on the liquid crystal panel assembly 300.

The signal controller 600 controls operations of the gate driver 400 and the data driver 500.

The display operation of such a liquid crystal display device will now be described in detail.

The signal controller 600 may control the input 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 properly processes the image signals R, G, and B according to the operating conditions of the liquid crystal panel assembly 300 based on the input image signals R, G, and B and the input control signal, and controls the gate control signal. After generating the CONT1 and the data control signal CONT2, the gate control signal CONT1 is sent to the gate driver 400, and the data control signal CONT2 and the processed image signal DAT are transmitted to the data driver 500. Export to

The gate control signal (CONT1) includes a gate-on voltage vertical synchronization start signal (STV) for instructing the start of output of the (V _on), the gate-on voltage gated clock signal that controls the output timing of the (V _on) (CPV) and the gate-on An output enable signal OE or the like that defines the duration of the voltage V _on .

The data control signal CONT2 includes a horizontal synchronization start signal STH indicating the start of input of the image data DAT, a load signal LOAD for applying a corresponding data voltage to the data lines D ₁ -D _m , and a common voltage ( the polarity of the data voltages for the V _com) (hereinafter the "polarity of data voltage for the common voltage" reduction include inversion signal (RVS), and the data clock signal (HCLK), such as to reverse that) the term "polarity of a data voltage" do.

The data driver 500 sequentially receives and shifts the image data DAT for one row of pixels according to the data control signal CONT2 from the signal controller 600, and the gray voltage from the gray voltage generator 800. The grayscale voltage corresponding to each image data DAT is selected to convert the image data DAT into a corresponding data voltage, and then apply the grayscale voltage to the corresponding data lines D ₁ -D _m .

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. ) Turns on the switching element Q connected thereto, so that the data voltage applied to the data lines D ₁ -D _m is applied to the corresponding pixel through the turned-on switching element Q.

The difference between the data voltage applied to the pixel and the common voltage V _com is shown as the charging voltage of the liquid crystal capacitor C _LC , that is, the pixel voltage. The arrangement of the liquid crystal molecules varies according to the magnitude of the pixel voltage, thereby changing the polarization of light passing through the liquid crystal layer 3. 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.

After one horizontal period (or “1H”) (one period of the horizontal sync signal H _sync , the data enable signal DE, and the gate clock CPV), the data driver 500 and the gate driver 400 are next. The same operation is repeated for the pixels in the row. 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). "). At this time, the polarity of the data voltage flowing through one data line is changed according to the characteristics of the inversion signal RVS even in one frame (eg, "row inversion", "point inversion"), or the voltage of the data voltage applied to one pixel row. The polarities can also be different (eg "heat inversion", "point inversion").

Next, the common voltage generator of the liquid crystal display according to the exemplary embodiment of the present invention will be described in detail with reference to FIGS. 3 and 4.

3 is a common voltage generator of a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 4 is a schematic diagram of a liquid crystal display according to an exemplary embodiment of the present invention.

As shown in FIG. 3, the common voltage generator 700 according to an exemplary embodiment of the present invention may include a plurality of resistor strings connected in parallel to an operational amplifier OP and a non-inverting terminal of the operational amplifier OP. And a plurality of multi-switches 710 and 720 connected to the output terminal of the operational amplifier OP.

Here, the operational amplifier OP is a differential amplifier, the inverting terminal of the amplifier OP is connected to the feedback voltage V _comf through the resistor R4, and the multi-switch 710 is the amplifier OP. ), And the multi-switch 720 is connected between the resistor R6 and the resistor R7.

The plurality of resistor rows R1-R3 and VR are connected between the reference voltage AVDD and the ground voltage, and the variable resistor VR is connected in parallel with the resistor R3 to amplifier together with the resistors R1 and R2. The voltage input to the non-inverting terminal of the OP is adjusted, and the input voltage is substantially the same as the common voltage V _com first input to the liquid crystal panel assembly 300.

Since the multi-switch 710 is connected to the output terminal of the operational amplifier (OP), and the multi-switch 720 is connected between the resistor (R6) and the resistor (R7), the output voltage (V _com21 ) of the multi-switch 720 -V _com28 is lower than the output voltage V _com11 -V _com18 of the multi-switch 710. Therefore, the output voltage may be subdivided within the multi-switches 710 and 720, and the voltage may be subdivided among the multi-switches to further maximize the compensation effect.

In this case, the multi-switches 710 and 720 may _emit , for example, eight output voltages V _com11 to V _com18 and V _{com21 to} V _com28 , _respectively , and the number of outputting these voltages may be adjusted as necessary. That is, each of the multi-switches 710 and 720 can each output one to eight outputs, and the adjustment of these outputs may be performed by an operator directly or by sending control signals from the signal controller 600 or other components. have.

The common voltage generator 700 receives the feedback voltage V _comf from the short points SP1-SP12 of the liquid crystal panel assembly 300, _{corrects the} feedback voltage, and provides the corrected voltage to the data driving integrated circuit.

As shown in FIG. 4, the feedback voltage V _comf may be output from at least one of the short points SP1 _{-SP12 of the} liquid crystal panel assembly 300, and the short points SP1 -SP12 are the liquid crystal panel assembly. The number 300 of data drive ICs is provided at 300 on the left side of each of the data drive ICs.

The common voltage generator 700 receives the feedback voltage V _comf and compensates the difference from the common voltage V _com to output the common voltages V _com11 to V _com18 and V _{com21 to} V _com28 . The output common voltages V _com11 -V _com18 and V _com21 -V _com28 are input to the data driver 500 as shown in FIG. 4, and the input common voltages V _com11 -V _com18 and V _com21 -V are input. _com28 is applied to the liquid crystal panel assembly 300 through a dummy channel among data channels provided in the data driver IC.

In this case, when the feedback voltage V _comf is drawn from all the short points SP1 to SP12 as described above, the outputs of the multi-switches 710 and 720 may be output accordingly. For example, each of six outputs may be applied, and all 12 common voltages V _com 'may be applied through dummy channels of the data driving ICs # 1-# 12. In this case, the common voltages may be drawn out. It is preferable to add the corrected common voltage at a position close to the short points SP1-SP12.

In this manner, the flicker and the afterimage may be improved by further compensating for the resistance and the kickback voltage distributed in the display panel assembly 300.

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 (6)

A liquid crystal panel assembly having a plurality of pixels and a switching element connected thereto; A gray voltage generator for generating a plurality of gray voltages; A data driver which selects a gray voltage corresponding to an image signal among the gray voltages as a data voltage and applies it to the pixel; A common voltage generator which generates a common voltage and applies it to the liquid crystal panel assembly. Including, The common voltage generator An operational amplifier, and First and second multi-switches connected to an output terminal of the operational amplifier Containing Liquid crystal display. In claim 1, And the first multi-switch is connected to an output terminal of the operational amplifier, and the second multi-switch is connected to a center of a resistor string connected in series between the output terminal and a ground terminal. In claim 2, And the first and second multi-switches emit first to eighth corrected common voltages, respectively. In claim 3, The liquid crystal panel assembly includes a plurality of short circuit points, The operational amplifier receives a feedback voltage from at least one of the short points. Liquid crystal display. In claim 4, The data driver includes a plurality of data driver integrated circuits, Output voltages of the first and second multi-switches are applied to the liquid crystal panel assembly through the dummy channel of the data driving integrated circuit. Liquid crystal display. In claim 1, And the operational amplifier is a differential amplifier.

Images