KR20040078297A - Liquid crystal display and driving method thereof - Google Patents

Abstract

PURPOSE: An LCD device is provided to change a common voltage according to an externally applied control signal, without attaching a variable resistance to an LCD device body. CONSTITUTION: An LCD assembly(300) consists of plural gate lines(G1-Gn), plural data lines(D1-Dm), and plural pixels arrayed in matrix type. A data driver(500) selects a gradation voltage corresponding to image data among plural gradation voltages, and applies the selected gradation voltage to the pixels as a data voltage. A common voltage generator(700) generates a common voltage, and supplies the common voltage to the pixels. A signal controller(600) supplies the image data, and generates a control signal for controlling the image data, then supplies the control signal to the data driver(500).

Description

Liquid crystal display and its driving method {LIQUID CRYSTAL DISPLAY AND DRIVING METHOD THEREOF}

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

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 form an electric field in the liquid crystal layer, and the intensity of the electric field is adjusted to control the transmittance of light passing through the liquid crystal layer to obtain a desired image. At this time, in order to prevent deterioration caused by the application of an electric field in one direction 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, or dot.

Meanwhile, when the polarity of the data voltage is inverted with respect to the common voltage, flicker occurs due to the asymmetry between the positive and negative polarities.

In order to minimize the flicker phenomenon, the common voltage is controlled by using a variable resistor. That is, different common voltages are set according to the characteristics of the elements and the characteristics of the liquid crystal display.

However, the use of the variable resistor is exposed to the variable resistor during production, resulting in quality problems, precision by manual adjustment of the variable resistor, increase in cost due to the use of the variable resistor, mechanical resistance value of the variable resistor. It causes problems such as foreign matters to enter the hole (hole) for adjusting the, and limit of the height of the part. In addition, as the size of the liquid crystal display becomes larger, it becomes difficult to adjust the variable resistance while observing the state of the image quality, and the freedom of product design when designing a stylish appearance due to the variable resistance attached to the front or the rear of the liquid crystal display body. Acts as a lowering factor. In addition, the variable resistor is damaged or broken during the adjustment of the common voltage to increase the defective rate of the product.After completing the adjustment work, the adjustment state of the variable resistor is shifted due to external shock or vibration. The reliability of the product is also low.

Therefore, the technical problem to be achieved by the present invention is to set a common voltage suitable for LCD products without using a variable resistor.

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 detailed circuit diagram of a signal input unit and a common voltage generator according to an embodiment of the present invention.

According to an aspect of the present invention, a liquid crystal display includes a plurality of gate lines, a plurality of data lines, and a plurality of pixels connected to the gate lines and the data lines and arranged in a matrix form. A liquid crystal panel assembly, a data driver which selects a gray voltage corresponding to image data among a plurality of gray voltages and applies the data voltage to the pixel, a common voltage generator which generates a common voltage and supplies the same to the pixel, and the image data Is provided to the data driver, and generates a control signal for controlling the image data and provides the signal to the data driver, the common voltage generation unit increases the counting value according to the state of the digital signal from the outside Or decreases the voltage corresponding to the counting value. Output as the supply voltage.

The liquid crystal display further includes a signal input unit including a plurality of switches, wherein the signals are generated by the operation of the switches and the states of the signals generated by the operations of the switches are different from each other.

Preferably, the number of switches is two.

In the present invention, the signal input unit may further include a noise removing unit.

The common voltage generator is configured to increase or decrease a counting value according to a state of a signal from the signal input unit, a memory in which a digital value corresponding to the counting value is stored, and the digital value stored in the memory as an analog value. It is preferable to include a D / A converter which converts the output. The common voltage generator may further include a buffer connected to the D / A converter.

In the liquid crystal display of the present invention, the voltage value change range of the common voltage according to the change in the counting value may be 0.88V.

According to an aspect of the present invention, there is provided a driving method of a liquid crystal display including a plurality of pixels, the method comprising generating a signal in a first or second state according to a user's operation, and counting a value according to the state of the signal. Increasing and decreasing, storing the counting value in a digital state, and converting the stored digital value into an analog value and supplying the pixel as a common voltage.

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.

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 common voltage generation connected thereto. The unit 700 includes a signal input unit 710 connected to the common voltage generator 700, a gray voltage generator 800 connected to the data driver 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 , 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 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 entire 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 superimposing 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 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.

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.

The gray voltage generator 800 generates a plurality of gray voltages V + and V− of the positive (+) and the negative (-) related to the luminance of the liquid crystal display.

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 selects the gray voltages V + and V− from the gray voltage generator 800 and applies them to the pixel as data signals.

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.

The common voltage generator 700 generates a common voltage V _com and supplies it to the liquid crystal panel assembly 300.

In addition, the signal input unit 710 generates and supplies a driving signal to the common voltage generator 700 to generate a common voltage V _com having an appropriate value.

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.

The gate control signal CONT1 includes a vertical synchronization start signal STV for indicating the start of output of the gate-on pulse (high period of the gate signal), a gate clock signal CPV for controlling the output timing of the gate-on pulse, and a gate-on pulse. And an output enable signal OE that defines the width of the signal.

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 gray voltage generator 800 generates a plurality of gray voltages related to the luminance of the liquid crystal display and applies them to the data driver 500.

The data driver 500 sequentially receives image data R ′, G ′, and B ′ corresponding to one row of pixels according to the data control signal CONT2 from the signal controller 600, and generates a gray 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 one row of switching elements Q connected thereto is turned on (this period is referred to as "1H" or "1 horizontal period ( horizontal period) "and equal to one period of the horizontal synchronization signal Hsync, the data enable signal DE, and the gate clock CPV], and the data driver 400 stores each data voltage as 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.

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").

The common voltage generator 700 generates a common voltage V _com of a corresponding magnitude based on a control signal from the outside and supplies the generated common voltage V _com to the liquid crystal panel assembly 300.

The signal input unit 710 generates a control signal according to a driving signal from the outside generated by the user and applies the control signal to the common voltage generator 700.

Next, the signal input unit and the common voltage generator will be described in detail with reference to FIG. 3.

3 is a detailed circuit diagram of a signal input unit and a common voltage generator according to an embodiment of the present invention.

As shown in FIG. 3, the signal input unit 710 includes two switches, that is, an up switch SW1 and a down switch SW2, two resistors R1 and R2, and a noise removing unit 711. The up switch SW1 and the down switch SW1 are connected in series between the power supply VDD and the ground, and the resistors R1 and R2 are connected in parallel to each of these switches SW1 and SW2. The noise removing unit 711 inputs the common terminals of the switches SW1 and SW2 and the resistors R1 and R2.

As shown in FIG. 3, the common voltage generator 700 is connected to a digital potentiometer 704 and a digital potentiometer 704 connected to the noise canceling unit 711 of the signal input unit 710. A voltage divider (R5, R6) consisting of two resistors (R5, R6) connected in series between Vcc) and ground, and a buffer (BF1) connected to the voltage divider (R5, R6) and outputting a common voltage (V _com ). .

The digital potentiometer 704 is a voltage divider consisting of two resistors R3 and R4 connected in series between the power supply VDD and ground, a controller 701 connected to the voltage divider, a memory unit 702 connected to the controller 701, And a digital-to-analog converter (hereinafter, referred to as a "D / A converter") 703 connected to the memory unit 702.

The operation of the signal input unit 710 and the common voltage generator 700 according to the embodiment of the present invention having such a structure will be described.

First, the signal input unit 710 generates a high voltage or a low voltage according to the operation of the up switch SW1 or the down switch SW2. That is, the power supply voltage VDD is generated when the up switch SW1 is pressed by the user, and the ground voltage is generated when the down switch SW2 is pressed. The signals from the switches SW1 and SW2 are supplied to the noise removing unit 711 to remove noise components such as ripple, and then transmitted to the potentiometer 704 of the common voltage generator 700.

The signal transmitted from the signal input unit 710 is applied to the controller 701 by adjusting the voltage level by the resistors R3 and R4 which are divided voltage resistors. The controller 701 counts the input pulses according to the state of the input signal. That is, according to an exemplary embodiment of the present invention, the counting value may be a reference value, for example, an initial value of "0", and counted up and down 32 up and down based on this. Therefore, when the up switch SW1 is turned on and the "high" signal is input, the controller 701 increases the value "1" from the current counting value, and conversely, if the "low" signal is input due to the on operation of the down switch SW2. , Subtract "1" from the current counting value. At this time, the value counted by the control unit 701 is stored in the memory unit 702 in a digital state.

Then, the data stored in the memory unit 702 is applied to the D / A converter 703 to be converted into a voltage of a corresponding analog state, and level-adjusted through the voltage dividers R5 and R6 to the buffer server BF1. And is applied to the liquid crystal panel assembly 300 at a common voltage V _com .

As in the embodiment of the present invention, when the counting steps of the up switch SW1 and the down switch SW2 each consist of 32, the total voltage range corresponding thereto is, for example, about 0.88V, and the control unit 701 The voltage corresponding to the counting value is applied to the buffer unit BF1 through the memory unit 702 and the D / A converter 703.

In this way, the inspector operates the switch SW1 or SW2 while visually observing the screen state of the liquid crystal display to obtain an appropriate common voltage V _com , and the obtained common voltage V _com is fixedly fixed to the assembly 300. Supplied to.

The common voltage V _com adjustment operation is performed during an evaluation test for evaluating the operation performance of the liquid crystal display device after the panel assembly process of the liquid crystal display device, and inputs an input device such as a keyboard among external devices used for the evaluation test signal input unit 710. It is used as). That is, two of the input keys attached to the input device are arbitrarily set as adjustment keys, and the inspector presses the up switch (SW1) or the down switch (SW2) while visually confirming the image quality of the liquid crystal display to display the best image quality. Until the common voltage V _com is adjusted.

Therefore, it is not necessary to mount or provide a separate signal input section for adjusting only the common voltage V _com . In this case, the signal input unit 710 is connected to the input terminal of the common voltage generator 700 by using a connector or by connecting a signal line to a point on the PCB. Therefore, the common voltage generator 700 may be mounted at an appropriate position such as a gate PCB, a data PCB, or a liquid crystal panel assembly.

As such, since the common voltage is changed according to a separate adjustment signal applied from the outside, a simple adjustment operation improves the efficiency and accuracy of the operation, thereby effectively suppressing flicker generation, thereby improving the reliability of the product. In addition, since the variable resistor does not need to be attached to the liquid crystal display body, the degree of freedom in design is increased, resulting in high quality products.

In particular, even in a large-sized liquid crystal display device, the common voltage adjustment operation is easily performed, and thus the flicker removal efficiency and the work efficiency are excellent.

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 (8)

A liquid crystal panel assembly comprising a plurality of gate lines, a plurality of data lines, and a plurality of pixels connected to the gate lines and the data lines, respectively, and arranged in a matrix form; A data driver which selects a gray voltage corresponding to image data among a plurality of gray voltages and applies the same to the pixel as a data voltage; A common voltage generator configured to generate a common voltage and supply the common voltage to the pixel; A signal controller configured to provide the image data to the data driver and generate a control signal for controlling the image data and provide the control signal to the data driver Including; The common voltage generator increases or decreases a counting value according to a state of a digital signal from the outside, and outputs a voltage corresponding to the counting value as the common voltage. Liquid crystal display. In claim 1, Further comprising a signal input unit having a plurality of switches, the signal is generated by the operation of each switch and the state of the signal generated by the operation of the plurality of switches are different Liquid crystal display. In claim 2, The number of the switch is two liquid crystal display device. In claim 2, The signal input unit further includes a noise removing unit. In claim 1, The common voltage generator, A control unit which increases or decreases a counting value according to a state of a signal from the signal input unit, A memory that stores a digital value corresponding to the counting value, and A D / A converter converting the digital value stored in the memory into an analog value and outputting the analog value Liquid crystal display comprising a. In claim 5, The common voltage generator further includes a buffer connected to the D / A converter. In claim 1, The voltage value change range of the common voltage according to the change in the counting value is 0.88V. A driving method of a liquid crystal display device including a plurality of pixels, Generating a signal in a first or second state according to a user's operation, Increasing or decreasing a counting value according to the state of the signal, Storing the counting value in a digital state, and Converting the stored digital value into an analog value and supplying the pixel as a common voltage Method of driving a liquid crystal display comprising a.