KR20070014535A - Liquid crystal display and driving method the same - Google Patents

Abstract

A liquid crystal display(LCD) device and a driving method thereof are provided to suppress an afterimage and a flicker by varying a common voltage, when a peripheral temperature rises. A liquid crystal display device includes an LCD panel and a common voltage generator(270). The common voltage generator generates a common voltage, which is supplied to a common electrode of the LCD panel. The common voltage generator includes a common voltage varying unit(262), which varies the common voltage, when a peripheral temperature is varied. The common voltage generator includes dividing resistors(R1,R2,R3), which are series-connected between a source voltage and a ground voltage. The common voltage generator includes a variable resistor(VR1) and an operational amplifier(OP-Amp). The variable resistor is connected to a node between the dividing resistors. The operational amplifier is connected to a capacitor, which is connected to the node.

Description

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

1 is a block diagram illustrating a driving unit of a liquid crystal display according to an exemplary embodiment of the present invention.

2 is a view showing a common voltage generator according to an embodiment of the present invention;

3 is an equivalent circuit diagram of one pixel area of a liquid crystal display according to an embodiment of the present invention;

4 is a view showing ΔVp characteristics according to temperature of a liquid crystal display according to an exemplary embodiment of the present invention.

5 is a view showing the Vth characteristics according to the temperature of the diode according to an embodiment of the present invention,

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

<Code Description of Main Parts of Drawing>

100: liquid crystal display device 200: display unit

210: liquid crystal display panel 212: thin film transistor substrate

214: color filter substrate 220: gate TCP

222: gate driver IC 230: gate printed circuit board

240: data TCP 242: data driver IC

250: data printed circuit board 252: digital video card

254 control unit 262 common voltage change unit

270: common voltage generator 280: driver

300: backlight unit 310: lamp unit

312 lamp 314 lamp reflector

320: light guide plate 330: first mold frame

340: second mold frame 350: optical sheet

360: reflective sheet 370: bottom chassis

400: top chassis

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 an apparatus 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 thin film transistor connected to the gate line and the data line, and a pixel electrode connected to the thin film transistor, respectively.

In order to drive the liquid crystal display, an inversion method of periodically inverting the polarity of the common voltage of the pixel voltage applied to the pixel electrode is used. As the inversion method, for example, there is a dot inversion method that inverts the polarity of the common voltage of the pixel voltage between adjacent pixel electrodes 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. This 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 common voltage occurs. This phenomenon is further exacerbated by preventing heat from being emitted from the liquid crystal display when the liquid crystal display is mounted on 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.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a liquid crystal display and a driving method thereof for improving display quality.

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

The common voltage generator may further include voltage dividers connected in series between a supply voltage and a base voltage, and the common voltage changer may be connected in series with a voltage divider connected to the base voltage among the voltage dividers.

The common voltage generator may further include a variable resistor connected to a contact point of the divided voltage resistors between the supply voltage and the common voltage changer, and an operational amplifier connected to a capacitor connected to the contact point.

The common voltage changer may be an electronic device in which a threshold voltage decreases as the temperature increases and the threshold voltage increases as the temperature decreases.

The common voltage variable part may include at least one diode.

The display device may further include a gate driver IC driving the gate line of the liquid crystal display panel and a data driver IC 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 varied according to temperature change by using a common voltage changer included in the common voltage generator and supplying the common voltage to the liquid crystal display panel. A driving method of a liquid crystal display device is provided.

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 according to the temperature change using the common voltage changer included in the common voltage generator is relatively low by the diode whose threshold voltage decreases as the temperature increases. Generating a common voltage and generating a relatively high common voltage by the diode in which 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 illustrating a driving unit of a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 1, the driving unit 280 of the liquid crystal display according to the exemplary embodiment of the present invention may include a gate driver IC 222 and an analog image signal for sequentially driving the gate line GL of the liquid crystal display panel 210. Digital video card 252 for converting a digital video signal DD into a digital video signal DD, a data driver IC 242 and a gate driver IC 222 for supplying a data signal to a data line DL of the liquid crystal display panel 210. And a control unit 254 for controlling the data driver IC 242, and a common voltage generator 270 for supplying the common voltage Vcom to the data driver IC 242.

The gate driver IC 222 is a shift register (not shown) that sequentially generates scan pulses in response to a gate control signal GCS input from the controller 254 and a level shifter for shifting a voltage to a level suitable for driving liquid crystals. (Not shown). In response to the scan pulse input from the gate driver IC 222, the data voltage on the data line DL is supplied to the pixel electrode by the thin film transistor TFT. The gate driver IC 222 may be directly formed on the liquid crystal display panel 210.

The digital video card 252 converts an input analog video signal into a digital video signal DD and detects the horizontal and vertical synchronous signals H and V included in the digital video signal DD to detect the respective signals DD and H. , V) are output to the controller 254.

The data driver IC 242 receives the data control signal DCS together with the red (R), green (G), and blue (B) digital video signals from the controller 254. The data driver IC 242 latches the red (R), green (G), and blue (B) digital video signals in synchronization with the data control signal (DCS), and then latches the red (R) and green (G) signals. ), The blue (B) digital video signal is corrected according to the gamma voltage. The data driver IC 242 converts the red (R), green (G), and blue (B) digital image signals corrected by the gamma voltage into data signals, and converts the data signals to the data lines DL for each line. Supply.

The controller 254 receives the digital video signal DD from the digital video card 252 and outputs the digital video signal DD to the data driver IC 242. In addition, the controller 254 generates the data control signal DCS and the gate control signal GCS by using the horizontal and vertical synchronization signals H and V input from the digital video card 252 to generate the data driver IC 242. ) And the timing of the gate driver IC 222. The data control signal DCS is supplied to the data driver IC 242, and the gate control signal GCS is supplied to the gate driver IC 222. The controller 254 may be formed on the data printed circuit board 250.

The common voltage generator 270 supplies the common voltage Vcom for driving the liquid crystal display panel 210 to the data driver IC 242 using the supply voltage generated by the DC / DC converter (not shown). . The common voltage generator 270 may be formed on the data printed circuit board 250.

To this end, as shown in FIG. 2, the common voltage generator 270 may include first to third resistors R1, R2, and R3 connected in series between the supply voltage AVDD and the base voltage GND. The common voltage shifting unit 262 is connected between the second and third resistors R2 and R3 in series with the second and third resistors R2 and R3.

The first to third resistors R1, R2, and R3 divide the supply voltage AVDD. In this case, the number of resistors may vary depending on the liquid crystal display.

The common voltage changer 262 varies the common voltage according to the temperature change of the liquid crystal display. To this end, the common voltage variable part 262 includes a diode D1. Here, the number of diodes may vary depending on the liquid crystal display.

On the other hand, as shown in FIG. 3, the thin film transistor substrate of the liquid crystal display device has the gate lines Gn-1 and Gn and the data lines Dm and Dm + 1 insulated by a gate insulating film (not shown) to cross each other. It is formed to be. At this time, the pixel region is defined by the intersection of the gate lines Gn-1 and Gn and the data lines Dm and Dm + 1.

In the pixel region, a thin film transistor TFT for selectively supplying the pixel voltage input from the data lines Dm and Dm + 1 to the liquid crystal is formed. For this purpose, the gate electrode G of the thin film transistor TFT is connected to the gate line Gn, the source electrode S of the thin film transistor TFT is connected to the data line Dm, and the drain of the thin film transistor TFT 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 Gn-1, and the parasitic capacitance Cgd is formed between the gate electrode G and the drain electrode D due to misalignment. do. The liquid crystal capacitor Clc and the storage capacitor Cst act as loads to which the liquid crystal display device should be driven.

When the thin film transistor TFT is operated by applying a gate on voltage to the gate electrode G connected to the gate line Gn, the source electrode S receives the pixel voltage received from the data line Dm. 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, and is applied to the potential difference between the pixel electrode P and the common electrode Com. An electric field is formed by this.

However, when the thin film transistor TFT is turned on, the voltage applied to the liquid crystal capacitor Clc and the storage capacitor Cst should be maintained even after the thin film transistor TFT is turned off. ) And distortion of the pixel voltage applied to the pixel electrode P due to the parasitic capacitance Cgd between the drain electrode D and the drain electrode D. FIG. The distorted voltage is called a kickback voltage (ΔVp), and the kickback voltage is obtained by the following equation (1).

As shown in FIG. 4, the kickback voltage increases as the temperature increases as the LCD is driven for a long time. The diode D1 changes the common voltage according to the kickback voltage change. More specifically, as shown in FIG. 5, the threshold voltage Vth of the diode D1 is lowered as the temperature increases. That is, when the temperature rises, the voltage output from the common voltage shifter is lowered due to the lowered threshold voltage Vth of the diode D1, thereby lowering the common voltage. On the contrary, when the temperature decreases, the voltage output from the common voltage variable part increases, thereby increasing the common voltage.

Initial optimum common voltage (V) Optimum common voltage (V) after 10 hours 10 hours later Common voltage (V) After 10 hours the common voltage (V) of the liquid crystal display of the present invention Sample # 1 4.543 4.533 4.543 4.532 Sample # 2 4.462 4.444 4.462 4.443

As shown in Table 1, 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 was 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 the first sample (sample # 1) and the second sample (sample # 2). 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 increases after 10 hours, the common voltage of the liquid crystal display of the present invention is a voltage of 0.011V and 0.019V for the first sample (sample # 1) and the second sample (sample # 2), respectively. A drop occurred. In other words, when the first sample (Sample # 1) and the second sample (Sample # 2) for 10 hours, respectively, compared to the optimum common voltage of 4.533V and 4.444V, almost the same level. That is, the common voltage due to the diode D1 is lowered, thereby ensuring an optimum common voltage, which does not cause a problem such as afterimage or flicker.

Meanwhile, the common voltage generator 270 includes the variable resistor VR1 connected to the contacts of the first and second resistors R1 and R2, and the capacitor C1 connected to the contact of the first and second resistors R1 and R2. And the sixth and seventh resistors R6, which are connected to the operational amplifier OP-Amp and the output terminal of the operational amplifier OP-Amp and are connected in series between the supply voltage AVDD and the ground voltage GND. R7) is further included.

The variable resistor VR1 is a variable resistor VR1 whose resistance is adjusted by a user so as to adjust the common voltage Vcom applied to the common electrode according to the liquid crystal display.

The operational amplifier OP-Amp amplifies the input voltage according to an amplification ratio determined by the fourth resistor R4 and the fifth resistor R5. The feedback voltage Vcomf of the common voltage is supplied to the inverting input terminal of the operational amplifier OP-Amp. In addition, the non-inverting input terminal of the operational amplifier OP-Amp receives the charging voltage of the capacitor C1 charged with the voltage output from the common voltage varying unit 262.

The sixth and seventh resistors R6 and R7 divide the voltage output from the operational amplifier OP-Amp at the contact of the sixth and seventh resistors R6 and R7 to output the common voltage Vcom. The number of resistors may vary depending on the common voltage Vcom of the liquid crystal display.

Next, a liquid crystal display of the present invention will be described with reference to FIG.

Referring to FIG. 6, the liquid crystal display device 100 according to an exemplary embodiment of the present invention fixes the backlight unit 300 to supply light to the display unit 200 and the display unit 200 to the backlight unit 300. The top chassis 400 includes a display unit 200 for displaying an image.

The backlight unit 300 reflects the lamp unit 310 that generates light, the light guide plate 320 that guides the light to the liquid crystal display panel 210, and the light emitted from the light guide plate 320 toward the light guide plate 320. The reflective sheet 360 is included.

The lamp unit 310 includes at least one lamp 312 for generating light and a lamp reflector 314 for reflecting light generated from the lamp 312 in the direction of the light guide plate 320, and on one side of the light guide plate 320. Is placed on. Alternatively, the lamp unit 310 may be disposed on both side surfaces of the light guide plate 320 facing each other in response to the required luminance.

The lamp 312 is composed of at least one cold cathode fluorescent lamp having a rod shape. The lamp reflector 314 is made of a material having a high reflectance or has a structure in which a reflecting member is coated on a cover surface covering the lamp 312, thereby reflecting light generated from the lamp 312 toward the light guide plate 320. Improve the efficiency.

The light guide plate 320 diffuses the light incident from the lamp 312 to output uniform light to the liquid crystal display panel 210. The reflective sheet 360 is disposed under the light guide plate 320 and is formed to have a size corresponding to the light guide plate 320 by coating a base material with a high reflectance.

On the other hand, the backlight unit 300 further includes an optical sheet 350 to be mounted on the light guide plate 320 to improve the brightness and uniformity of the light emitted from the light guide plate 320.

In addition, the backlight unit 300 further includes a first mold frame 330 for accommodating the lamp unit 310 and the light guide plate 320. A bottom chassis 370 may be further provided inside the first mold frame 330 for firmness and heat dissipation of the backlight unit 300. The second mold frame 340 for fixing the optical sheet 350 is mounted on the upper sidewall of the first mold frame 330. The display unit 200 is mounted on an upper portion of the second mold frame 340, and a top chassis 400 for preventing separation and flow of the display unit 200 is coupled to the first mold frame 330.

The display unit 200 includes a liquid crystal display panel 210 for displaying a screen of the liquid crystal display device 100 and a driver 280 for driving the liquid crystal display panel 210.

The liquid crystal display panel 210 includes a liquid crystal (not shown) for adjusting a transmission amount of incident light, a color filter substrate 214 for applying a common voltage to the liquid crystal, and a thin film transistor substrate 212 for applying a pixel voltage to the liquid crystal. .

The liquid crystal has dielectric anisotropy and refractive anisotropy, and the light transmittance is controlled by refracting rotation and light by the difference between the common voltage and the pixel voltage applied to the liquid crystal. The color filter substrate 214 includes red, blue, and green color filters (not shown), thereby implementing colors of the display. The thin film transistor substrate 212 includes a thin film transistor (not shown) and a pixel electrode (not shown) connected thereto, thereby applying a pixel voltage to the liquid crystal.

The driver 280 is electrically connected to the liquid crystal display panel 210 by a gate tape carrier package (TCP) 220 mounted with a gate driver IC 222 for driving the liquid crystal display panel 210. A data printed circuit board electrically connected to the liquid crystal display panel 210 by a data TCP 250 mounted with a gate printed circuit board 220 and a data driver IC 242 for driving the liquid crystal display panel 210. And 230.

As described above, the liquid crystal display device 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 generator to ensure the optimum common voltage by varying the common voltage when the temperature rises, so that image quality such as afterimages and flicker does not occur.

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; And a common voltage generating unit including a common voltage varying unit which generates a common voltage supplied to the common electrode of the liquid crystal display panel and changes the common voltage according to a temperature change. The method of claim 1, The common voltage generator further includes voltage divider resistors connected in series between a supply voltage and a base voltage; And the common voltage variable part is connected in series with a voltage divider connected to the base voltage among the voltage divider. The method of claim 2, The common voltage generation unit may include a variable resistor connected to a contact point of the divided resistors between the supply voltage and the common voltage change unit among the divided resistors; And an operational amplifier connected to the capacitor connected to the contact point. The method of claim 1, And the common voltage variable part is an electronic device in which a threshold voltage decreases as the temperature increases and the threshold voltage increases as the temperature decreases. The method of claim 1, The common voltage variable part comprises at least one diode. The method of claim 1, A gate driver IC driving the gate line of the liquid crystal display panel; And a data driver IC for driving data lines of the liquid crystal display panel. Generating a common voltage which varies according to a temperature change using a common voltage changer included in the common voltage generator; And supplying the common voltage to the liquid crystal display panel. The method of claim 7, wherein Generating the common voltage which is changed according to the temperature change by using the common voltage changer included in the common voltage generator, A method of driving a liquid crystal display device using at least one diode. The method of claim 8, Generating the common voltage which is changed according to the temperature change by using the common voltage changer included in the common voltage generator, Generate a relatively low common voltage by the diode, the threshold voltage of which decreases as the temperature rises; And generating a relatively high common voltage by the diode in which the threshold voltage increases as the temperature decreases.

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