KR20070052148A - Liquid crystal display and driving method thereof - Google Patents

Abstract

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

The present invention provides a liquid crystal display panel including a plurality of pixels and a switching element connected thereto, a gray voltage generator for generating a plurality of gray voltages, and a gray voltage corresponding to an image signal among the gray voltages as a data voltage. A data driver for applying a common voltage; and a common voltage generator for generating a common voltage and applying the same to the liquid crystal display panel, wherein the common voltage generator includes an operational amplifier having an inverting terminal, a non-inverting terminal, and an output terminal, and a common voltage generator for outputting the operational amplifier. The present invention relates to a liquid crystal display including a common voltage shifter connected in series between a terminal and an input unit for applying a common voltage to a liquid crystal display panel, and a driving method thereof.

As described above, the common voltage fluctuation part that changes the common voltage according to the temperature is provided to compensate for the common voltage according to the temperature, thereby preventing flicker and an afterimage of the liquid crystal display.

Liquid crystal display, common voltage, temperature, common voltage fluctuation part, diode

Description

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

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 an equivalent circuit diagram of one pixel area of a liquid crystal display according to an exemplary embodiment of the present invention.

5 is a diagram illustrating a kickback voltage ΔVp characteristic according to a temperature of a liquid crystal display according to an exemplary embodiment of the present invention.

6 is a diagram illustrating the threshold voltage (Vth) characteristics according to the temperature of the diode according to an embodiment of the present invention.

<Code Description of Main Parts of Drawing>

100: lower display panel 200: upper display panel

242: data drive IC 300: liquid crystal display panel

400: gate driver 500: data driver

600: signal controller 700: common voltage generator

800: gray voltage generator 901, 902, 903, 904: common voltage shifting unit

The present invention relates to a liquid crystal display device and a driving method thereof, and more particularly, to a liquid crystal display device and a driving method thereof for improving display quality.

In general, a liquid crystal display device is a device for displaying an image by adjusting the light transmittance of the liquid crystal using an electric field. To this end, the liquid crystal display includes a plurality of gate lines, a plurality of data lines crossing the gate lines, a switching element connected to the gate line and the data line, and a pixel electrode connected to the switching element, respectively.

In order to drive the liquid crystal display, an inversion method of periodically inverting a polarity of a common voltage of the pixel voltage applied to the pixel electrode is used. As an inversion method, for example, there is a dot inversion method inverting the polarity of the pixel voltage with respect to the common voltage between pixel electrodes adjacent to each other in the vertical and horizontal directions.

However, when the liquid crystal display is driven for a long time, the common voltage, which is a reference when driving the liquid crystal, is changed due to a temperature rise caused by the heat generation of the lamp, which causes a problem that only one polarity is applied to the liquid crystal. That is, since the common voltage level is not correct, a difference between the absolute pixel voltage of the positive pixel voltage with respect to the common voltage and the negative pixel voltage of the negative voltage with respect to the common voltage occurs. This phenomenon is further exacerbated by preventing the set from preventing heat emission from the liquid crystal display when the liquid crystal display is mounted in a set such as a TV. For this reason, an afterimage, flicker, etc. generate | occur | produce, and the display quality of a liquid crystal display device falls.

The technical problem to be achieved by the present invention is to solve the problems of the prior art to provide a liquid crystal display device and a driving method thereof with improved display quality.

In order to achieve the above object, the present invention generates a common voltage supplied to the liquid crystal display panel and the common electrode of the liquid crystal display panel, and includes a common voltage generation unit including a common voltage changer for changing the common voltage according to temperature change. Provided is a display device.

According to an exemplary embodiment, a liquid crystal display includes a liquid crystal display panel including a plurality of pixels and a switching element connected thereto, a gray voltage generator configured to generate a plurality of gray voltages, and a gray voltage corresponding to an image signal among the gray voltages. A data driver to select and apply a voltage to a pixel; and a common voltage generator to generate a common voltage and apply the same to a liquid crystal display panel, wherein the common voltage generator includes an operational amplifier having an inverting terminal, a non-inverting terminal, and an output terminal, and a common voltage. The generation unit includes a common voltage changer connected in series between an output terminal of the operational amplifier and an input unit for applying a common voltage to the liquid crystal display panel.

The common voltage change unit changes the common voltage according to the temperature change of the liquid crystal panel. In addition, the common voltage changer includes at least one diode.

The common voltage generator applies two or more different common voltages to the liquid crystal display panel. In addition, the common voltage changer is an electronic device in which a threshold voltage decreases as the temperature increases and the threshold voltage increases as the temperature decreases. The electronic device may be a PTC type or an NTC type thermistor.

The apparatus may further include a gate driver for driving the gate line of the liquid crystal display panel and a data driver IC for driving the data line of the liquid crystal display panel.

In order to achieve the above object, the present invention includes the steps of generating a common voltage that is changed in accordance with the temperature change using a common voltage changer included in the common voltage generator; A method of driving a liquid crystal display device including supplying the common voltage to a liquid crystal display panel using at least one diode is provided.

In addition, the common voltage generator includes applying a common voltage of two or more different sizes to the liquid crystal display panel.

In addition, the generating of the common voltage which is changed according to the temperature change by using the common voltage changer included in the common voltage generator may include using at least one diode.

In addition, the generating of the common voltage which is changed in accordance with the temperature change using the common voltage changer included in the common voltage generator may generate a relatively low common voltage by a diode whose threshold voltage decreases as the temperature increases. It may be a step of generating a relatively high common voltage by the diode that the threshold voltage increases as the temperature decreases.

Next, a preferred embodiment of the present invention will be described with reference to the drawings.

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.

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

The liquid crystal display panel 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 transmitting gate signals (also called scan signals) and data lines D ₁ transferring data signals. includes -D _m). gate lines (G ₁ -G _n) extend in a substantially row direction and are substantially parallel to the data lines (D ₁ -D _m) to each other and extending substantially in a column direction 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, in order 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 according to time (time division) so that the desired color can be spatially and temporally combined with the 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.

Polarizers (not shown) for polarizing light are attached to outer surfaces of at least one of the two display panels 100 and 200 of the liquid crystal display panel 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 display panel 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 display panel 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 (IC) to attach the TCP to the liquid crystal display panel 300, or use TCP. Instead, the integrated circuit chips may be directly attached onto a glass 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 display panel 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 display panel 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 is a horizontal synchronous 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. An inversion signal RVS and a data clock signal HCLK for inverting the polarity of the data voltage with respect to V _com (hereinafter referred to as the polarity of the data voltage by reducing the polarity of the data voltage with respect to the common voltage).

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 may move to the next 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 the data voltages to all the pixels. When one frame ends, the state of the inversion signal RVS applied to the data driver 500 is controlled so that the next frame starts and the polarity of the data voltage applied to each pixel is opposite to that of the previous frame. Frame inversion "), where the polarity of the data voltage flowing through one data line is changed depending on the characteristics of the inversion signal (RVS) (eg, inversion of a row, inversion of a point), or a data voltage applied to one pixel row. Polarity of It can vary (eg column inversion, dot 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 FIG. 3.

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.

As illustrated in FIG. 3, the common voltage generator 700 generates a common voltage Vcom for driving the liquid crystal display panel 300 using a supply voltage received from a DC / DC converter (not shown). do. In one embodiment, the common voltage Vcom is supplied to the data driver IC 242. The common voltage generator 700 may be provided on a data printed circuit board (not shown).

The common voltage generator 700 according to an exemplary embodiment of the present invention includes a plurality of resistors R0, R1, R21, R22, R23, and R24 connected between a supply voltage AVDD and a ground voltage GRD, and a liquid crystal. The panel 300 includes a plurality of operational amplifiers (OP-Amps) for generating common voltages of different magnitudes, and a plurality of common voltage shifters 901, 902, 903, and 904 connected thereto.

The resistors R0, R1, R21, R22, R23, and R24 divide and output the supply voltage AVDD, and the number or size thereof may vary depending on the product.

Many operational amplifiers (OP-AMPs) are differential amplifiers and have an inverting terminal, a non-inverting terminal and an output terminal. The non-inverting terminal is connected to the supply voltage AVDD through a plurality of resistors R0, R1, R4, R24, R23, R22, and R21. Feedback resistors R34, R33, R32, and R31 are connected between the inverting terminal and the output terminal of the operational amplifier OP-AMP.

The common voltage shifters 901, 902, 903, and 904 are connected between the output terminals of the operational amplifiers OP-Amp and the input terminals Vcom1, Vcom2, Vcom3, and Vcom4 of the liquid crystal display panel 300. The node between the output terminal of the operational amplifier OP-Amp and the common voltage changing units 901, 902, 903, and 904 serves as the common voltage measuring terminal Vcomf1, Vcomf2, Vcomf3, and Vcomf4.

The resistors R53 and R51 and the capacitors C3 and C1 are connected in series to the output terminal and the inverting terminal of some operational amplifiers OP-Amp. The capacitors C3 and C1 are connected with a feedback voltage Vfb which is fed back with a common voltage.

The feedback voltage Vfb is a shortcircuit point connecting the common electrode 200 to the common voltage input unit (not shown) of the lower panel 100 and the upper panel 200 in the liquid crystal display panel 300 ( Not shown). The common voltage feedback voltage Vfb may be a common voltage of the upper panel 200.

In one embodiment, the common voltage changer 901, 902, 903, or 904 may be a variable resistor, a diode, or a thermistor. The number of diodes or thermistors included in each common voltage change part 901, 902, 903, and 904 may vary depending on the liquid crystal display. Here, the thermistor may be a positive thermal coefficient (PTC) type that is proportional to temperature or a negative thermal coefficient (NTC) type that is inversely proportional to temperature as a device whose resistance changes with temperature.

The common voltage generator 700 includes a diode or thermistor in the common voltage changer 901, 902, 903, and 904 to compensate for the common voltage V _{com in} consideration of resistance according to temperature. Therefore, the optimum state for flicker can be maintained, so that the display quality can be improved even when the temperature of the liquid crystal display rises. In addition, the common voltage due to the feedback voltage Vfb may be compensated.

4 is an equivalent circuit diagram of one pixel area of the liquid crystal display according to the exemplary embodiment formed on the thin film transistor array panel. As illustrated, the gate lines G _n-1 and G _n and the data lines D _m and D _{m + 1} are insulated by a gate insulating film (not shown) and are formed to be orthogonal to each other. In this case, the pixel area is defined as an area surrounded by the gate lines G _n-1 and G _n and the data lines D _m and D _{m + 1} .

In the pixel region, a switching element Q for selectively supplying the pixel voltage input from the data lines D _m and D _{m + 1} to the liquid crystal is formed. To this end, the gate electrode G of the switching element Q is connected to the gate line Gn, the source electrode S of the switching element Q is connected to the data line Dm, and the drain of the switching element Q is connected. The electrode D is connected to the pixel electrode P. FIG.

A liquid crystal is formed between the pixel electrode P and the common electrode Com, which may be equivalently represented by the liquid crystal capacitor Clc. The storage capacitor Cst is formed between the pixel electrode P and the gate line G _n-1 , and the parasitic capacitance Cgd is formed between the gate electrode G and the drain electrode D due to misalignment or the like. do. The liquid crystal capacitor Clc and the storage capacitor Cst act as loads that the liquid crystal display device must drive.

When the switching device Q is operated by applying a gate-on voltage to the gate electrode G connected to the gate line Gn, the source electrode S converts the pixel voltage received from the data line Dm into the switching device Q. It is applied to the drain electrode D via the channel of. Then, the pixel voltage is applied to the liquid crystal capacitor Clc and the storage capacitor Cst through the pixel electrode P connected to the drain electrode D, respectively, to the potential difference between the pixel electrode P and the common electrode Com. An electric field is formed by this.

However, when the switching element Q is in the on state, the voltage applied to the liquid crystal capacitor Clc and the storage capacity Cst should continue even after the switching element Q is in the off state. Due to the parasitic capacitance Cgd between G) and the drain electrode D, distortion of the pixel voltage applied to the pixel electrode P occurs. The distorted voltage is called a kickback voltage (ΔVp), and the kickback voltage is obtained by the following equation.

As shown in FIG. 5, the kickback voltage increases as the liquid crystal display is driven for a long time and the temperature increases. As an embodiment of the common voltage varying portion 901, 902, 903, 904, the diode changes the common voltage according to this kickback voltage variation.

FIG. 6 is a diagram illustrating a threshold voltage (Vth) characteristic according to a temperature of a diode when the common voltage changer 901, 902, 903, or 904 includes a diode according to an embodiment of the present invention. More specifically, as shown in FIG. 6, the threshold voltage Vth of the diode decreases as the temperature increases. That is, as the temperature increases, the voltage output from the common voltage change part is lowered due to the lowered threshold voltage Vth of the diode, which lowers the common voltage. On the contrary, when the temperature decreases, the voltage output from the common voltage fluctuation part increases, thereby increasing the common voltage.

Experiments with two samples of the liquid crystal display showed that the initial optimum common voltages of the first sample (sample # 1) and the second sample (sample # 2) were 4.543V and 4.462V, respectively. After 10 hours, the optimum common voltage with increasing temperature changed to 4.533V and 4.444V for each of the first sample (Sample # 1) and the second sample (Sample # 2).

However, when the temperature increased after 10 hours, the common voltage of the conventional liquid crystal display device did not change for each of the first sample and the second sample. For this reason, the problem which only one polarity seems to be applied to a liquid crystal generate | occur | produced, and this caused the defect, such as an afterimage and flicker.

However, when the temperature increased after 10 hours, the common voltage of the liquid crystal display of the present invention caused a voltage drop of 0.011V and 0.019V for the first sample and the second sample, respectively. In other words, the values were almost the same when compared to the optimum common voltages 4.533V and 4.444V after 10 hours for the first sample and the second sample, respectively. In other words, the common voltage due to the diode was lowered to obtain an optimum common voltage, which did not cause any afterimage or flicker.

Therefore, in the liquid crystal display according to the present invention, the common voltage fluctuation part included in the common voltage generator 700 changes the common voltage Vcom applied to the common electrode according to the temperature of the liquid crystal panel 700, thereby making the optimum common voltage. By applying this, image quality can be improved by removing afterimage and flicker.

As described above, the liquid crystal display of the present invention includes a common voltage generator for changing the common voltage as the temperature rises. The liquid crystal display according to the present invention uses the common voltage changer to change the common voltage when the temperature rises, thereby ensuring an optimum common voltage, thereby preventing image degradation such as afterimage and flicker.

In the detailed description of the present invention described above with reference to the preferred embodiment of the present invention, those skilled in the art or those skilled in the art having ordinary knowledge of the present invention described in the claims to be described later It will be understood that various modifications and variations can be made in the present invention without departing from the spirit and scope of the art.

Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (9)

A liquid crystal display panel 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 display panel. Including, The common voltage generator An operational amplifier having an inverting terminal and a non-inverting terminal and an output terminal, and A common voltage changer connected to an output terminal of the operational amplifier and configured to vary the output voltage of the operational amplifier to apply a common voltage to the liquid crystal display panel Containing Liquid crystal display. In claim 1, And the common voltage changer changes the common voltage according to a temperature change of the liquid crystal panel. In claim 2, The common voltage variable part includes one or more diodes. In claim 3, And the common voltage generator is configured to apply common voltages of two or more different sizes to the liquid crystal display panel. In claim 1, The common voltage changer includes an electronic device in which a threshold voltage decreases as the temperature increases and the threshold voltage increases as the temperature decreases. In claim 5, The electronic device is a liquid crystal display device of the PTC type or NTC type thermistor. In claim 6, A gate driver for driving a gate line of the liquid crystal display panel, and Data driver IC for driving data lines of the liquid crystal display panel Liquid crystal display further comprising. A driving method of a liquid crystal display device comprising a liquid crystal display panel and a common voltage generator supplying a common voltage to the liquid crystal display panel. Generating a common voltage fluctuating according to a temperature change by using a common voltage changer included in the common voltage generator, and Supplying the liquid crystal panel by varying the common voltage generated by the common voltage changer using at least one diode; Method of driving a liquid crystal display comprising a. In claim 8, And the common voltage generator is configured to apply a common voltage having two or more different magnitudes to the liquid crystal display panel.

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