KR20110065754A - Liquid crystal display device and method of driving the same - Google Patents

Abstract

PURPOSE: A liquid crystal display device and a method of driving the same are provided to automatically compensate the characteristic change of a flicker by generating a compensated common voltage through voltage variation and supplying it a common line. CONSTITUTION: In a liquid crystal display device and a method of driving the same, a gate driving unit(130) supplies a gate signal to a gate line. A data driver(140) supplies a data signal to a data line. A timing controller(150) supplies the gate control signal to the gate driving unit. The timing controller supplies an RGB signal and a data control signal to the data driver. A compensation unit(160) generates a compensated common voltage by using the variation of a voltage which is measured from a common line and supplies it to the common line.

Description

Liquid Crystal Display and Driving Method {LIQUID CRYSTAL DISPLAY DEVICE AND METHOD OF DRIVING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a method of driving the liquid crystal display, in which variations in flicker characteristics are automatically compensated.

In general, a liquid crystal display (LCD) forms a liquid crystal layer between two substrates facing each other and is spaced apart from each other, and reconstructs the liquid crystal molecules of the liquid crystal layer by an electric field generated by applying a voltage to the electrodes of the two substrates. By arranging, it is an apparatus which expresses an image by the transmittance | permeability of the light which changes.

In particular, among such liquid crystal display devices, an active matrix liquid crystal display device in which pixels defined by gate lines and data lines intersecting with each other are arranged in a matrix form and a switching element and a pixel electrode are formed in each pixel is widely used. .

1 is a view of one pixel of a conventional active matrix liquid crystal display device.

As shown in FIG. 1, the conventional active matrix liquid crystal display device 10 includes a gate line GL and a data line DL, a thin film transistor T, a storage capacitor Cst, and a liquid crystal. Capacitor Clc is included.

The gate line GL and the data line DL cross each other to define the pixel area P, the thin film transistor T is connected to the gate line GL and the data line DL, and the storage capacitor Cst The liquid crystal capacitor Clc is connected to the thin film transistor T.

The liquid crystal capacitor Clc is configured of a pixel electrode (not shown), a liquid crystal layer, and a common electrode connected to the thin film transistor T, and serves to display a gray level corresponding to a data signal applied to the pixel electrode, and the storage capacitor (Cst) serves to keep the voltage of the pixel electrode constant by storing the data signal for one frame.

When the thin film transistor T is turned on by the gate signal Vg supplied to the gate line GL, the data signal supplied to the data line DL is applied to the pixel electrode Vp. Is applied.

That is, one electrode of each of the storage capacitor Cst and the liquid crystal capacitor Clc is connected to the drain electrode of the thin film transistor T so that the pixel voltage Vp corresponding to the data signal is applied, and the storage capacitor Cst and the liquid crystal are applied. The other electrode of each of the capacitors Clc is connected to the common electrode to apply a common voltage Vcom.

Here, the gate electrode and the drain electrode of the thin film transistor T are formed to overlap each other in structure, and the overlapping portion of the gate electrode and the drain electrode forms a gate-drain parasitic capacitor Cgd.

Therefore, the parasitic capacitor Cgd, the storage capacitor Cst, and the liquid crystal capacitor Clc are connected in parallel to the pixel electrode connected to the drain electrode of the thin film transistor T.

Here, in an ideal liquid crystal display device, the pixel voltage Vp should be maintained uniformly for one frame, but in practice, the pixel voltage Vp may vary due to various factors, which will be described with reference to the drawings.

FIG. 2 is a waveform diagram illustrating a gate signal and a pixel voltage of a conventional active matrix liquid crystal display, and is a waveform diagram of two consecutive frames of the liquid crystal display driven by frame inversion.

As shown in FIG. 2, when the thin film transistor T is turned on by a pulse of the gate signal Vg supplied to the gate line GL of FIG. 1, the thin film transistor T is turned on and supplied to the data line DL of FIG. 1. The data signal is applied to the pixel electrode to become the pixel voltage Vp.

Here, the change amount DVg of the gate signal Vg at the time when the pulse of the gate signal Vg ends, that is, at the time when the gate signal Vg changes from the high level voltage Vgh to the low level voltage Vgl. ), The charges of the capacitors connected to the pixel electrode are redistributed and thus the pixel voltage Vp is drastically reduced.

The variation amount of the pixel voltage Vp at the end of the pulse of the gate signal Vg is called a kickback voltage (Vkb), and the kickback voltage Vkb is calculated by the following equation (1) by charge redistribution. Can be.

Vkb = (Cgd / (Cst + Clc + Cgd)) * DVg --- Formula (1)

According to equation (1), the kickback voltage Vkb depends on the parasitic capacitor Cgd, the storage capacitor Cst, and the liquid crystal capacitor Clc.

Since the thin film transistor T is turned off while the pulse of the gate signal Vg is terminated to maintain the low level voltage Vgl, the pixel voltage Vp must be maintained at a constant value.

However, in practice, the pixel voltage Vp decreases slightly due to the off current Ioff of the thin film transistor T. The amount of change in the pixel voltage Vp caused by the off current of the thin film transistor T is converted into the leakage voltage Vlk. Let's call it.

As a result, during one frame, the pixel voltage Vp is not constantly maintained at a value corresponding to the data signal, and the pixel voltage variation amount ΔVp = Vkb + Vlk corresponding to the sum of the kickback voltage Vkb and the leakage voltage Vlk. Is reduced.

The pixel voltage variation ΔVp appears as a defect such as flicker in the image display of the liquid crystal display device. The flicker is an image that should be uniformly displayed by alternately displaying two images having different luminance. Distance means to be recognized as an image.

That is, as the pixel voltage changes from the voltage corresponding to the initial data signal by the pixel voltage variation amount ΔVp, different luminance is displayed.

In addition, in most liquid crystal display devices, inversion driving such as frame inversion, line inversion, and dot inversion is applied to prevent afterimages due to the fixing of electric charges. In this inversion driving, the pixel voltage variation amount ΔVp is different. As a result, the symmetry based on the common voltage Vcom is broken, and the flicker characteristic is further deteriorated.

For example, although the same data signal is input in the positive (+) N frame and the negative (-) (N + 1) frame in FIG. 2, the kickback voltage Vkb and the leakage voltage Vlk operate differently. Therefore, the common voltage Vcom does not exist in the symmetry line between the positive data signal and the negative data signal and is biased to one side, and the flicker is further deepened.

The asymmetry of the pixel voltage variation ΔVp can be minimized by appropriately adjusting the level of the common voltage Vcom. The adjustment of the common voltage Vcom is visually performed by the operator with the naked eye after the manufacture of the liquid crystal display device. While watching the video, adjust the variable resistance, etc., to find and fix the spot where the flicker is minimum (Optimal Common Voltage Manual Selection), and find the common voltage (Vcom) that automatically minimizes the flicker by using the flicker measurement equipment. This is accomplished through a method (optimum common voltage automatic selection method) for storing in a storage means such as an EEPROM of a driving integrated circuit (D-IC).

However, in the above two methods, since the common voltage Vcom is fixed by the measurement result when the liquid crystal display device is manufactured, there is a limit to compensate for the flicker characteristic that varies with temperature, which will be described with reference to the accompanying drawings. do.

3A and 3B illustrate changes in flicker characteristics according to temperature of a conventional LCD, and FIG. 4 illustrates changes in off current characteristics according to a temperature of a thin film transistor of a conventional LCD. .

As can be seen from Equation (1), the kickback voltage Vkb depends on the liquid crystal capacitor Clc, and the liquid crystal capacitor Clc depends on the temperature due to its inherent characteristics, so the kickback voltage Vkb varies depending on the temperature.

In addition, the leakage voltage Vlk also depends on the off current of the thin film transistor T. Since the off current of the thin film transistor T also varies with temperature, the leakage voltage Vlk also varies with temperature.

Therefore, the pixel voltage variation ΔVp and flicker characteristics of the liquid crystal display device vary depending on the temperature.

That is, as shown in Fig. 3A, in the first to third samples, the flicker of the liquid crystal display device after driving for 2 hours at 50C is larger than that of the initial liquid crystal display device immediately after the completion of manufacturing, and then at room temperature. One week later, the flicker of the liquid crystal display is slightly smaller than the flicker of the liquid crystal display after driving for 2 hours at 50C, but is not reduced to the flicker of the initial liquid crystal display.

That is, the flicker characteristics deteriorate when the liquid crystal display is driven at a high temperature or the like, and the flicker characteristics do not return to the initial flicker characteristics even after a long time at room temperature after operating at a high temperature.

As shown in FIG. 3B, the flicker of the liquid crystal display after driving for 96 hours under the environmental cycle conditions of cycling between high temperature, high temperature, high humidity, and high temperature, room temperature, and low temperature is higher than the flicker of the initial liquid crystal display device immediately after the completion of manufacturing. The flicker of the liquid crystal display after being driven for 96 hours at a lower temperature is larger than that of the early liquid crystal display.

That is, flicker characteristics deteriorate when the liquid crystal display is driven at high temperature, high temperature, high humidity, or environmental cycle conditions.

Here, the flicker of the liquid crystal display device may be expressed as the ratio of the AC component to the DC component of the luminance of the liquid crystal display device, and may be expressed in decibels (dB) or percentage (%).

For example, it can be calculated from the formula "flicker (dB) = 20 * log (Vac / Vdc)" or "flicker (%) = (Vac / Vdc) * 100".

On the other hand, as shown in Fig. 4, the current voltage (Ids-Vgs) characteristic curve of the thin film transistor of the liquid crystal display after driving under the reliability conditions of the driving 1 and the driving 2 is larger than the current voltage characteristic curve of the initial liquid crystal display. Move to the left.

That is, the threshold voltage of the thin film transistor of the initial liquid crystal display device is about 0.22V, and the threshold voltages of the liquid crystal display device after driving under the conditions of driving 1 and driving 2 are about -1.82V and about -1.18V, respectively. The threshold voltage shifted by 2.04 V and about -1.40 V (Vth shift), so the on current (Ion) of the thin film transistor increased from about 1.69 A to about 1.96 A and about 2.37 A, The off current (Ioff) of the transistor also increased from about 29.3fA initially to about 54.2fA and about 37.0fA.

Therefore, when the liquid crystal display is driven at a high temperature, the threshold voltage of the thin film transistor is changed, and accordingly, the off current of the thin film transistor is also changed to change the leakage voltage Vlk, and as a result, the flicker characteristic is changed.

As shown in FIGS. 3A, 3B, and 4, the flicker characteristics of the liquid crystal display are changed according to driving conditions such as temperature, and the variation of the flicker characteristics is not recovered.

That is, the optimum common voltage Vcom set at the completion of manufacturing of the liquid crystal display device to improve the flicker characteristics is not suitable for the flicker characteristics changed according to the driving of the liquid crystal display device in various environments. To compensate, it is necessary to set a new common voltage Vcom.

However, according to the aforementioned manual selection of the optimum common voltage and the automatic selection of the optimum common voltage, the optimum common voltage set at the completion of manufacturing of the liquid crystal display device is fixed, and thus the liquid crystal display device cannot be compensated for any longer. The problem of deterioration of the image quality occurs.

The present invention is to solve the above problems, by measuring the current pixel voltage fluctuation of the liquid crystal display device by the initialization of the liquid crystal display device or the user's selection and calculates the optimum common voltage therefrom and applied to the liquid crystal display device Accordingly, an object of the present invention is to provide a liquid crystal display device in which fluctuation in flicker characteristics due to driving is automatically compensated.

Another object of the present invention is to provide a method for driving a liquid crystal display device in which a pixel voltage variation is measured by scanning a gate signal with the common electrode floating.

In order to achieve the object as described above, the present invention, the gate wiring, data wiring and common wiring intersecting with each other, a thin film transistor connected to the gate wiring and the data wiring, the thin film transistor and the common wiring is connected to A liquid crystal panel comprising a storage capacitor and a liquid crystal capacitor; A gate driver supplying a gate signal to the gate wiring; A data driver supplying a data signal to the data line; A timing controller supplying a gate control signal to the gate driver and supplying an RGB signal and a data control signal to the data driver; Provided is a liquid crystal display including a compensator for generating a common voltage compensated using the voltage variation measured from the common line and supplying the common voltage to the common line.

Here, the compensation unit, and a common voltage supply unit for supplying a common voltage to the common wiring; A control switch controlling the connection of the common voltage supply unit and the common wiring; An operational amplifier including a non-inverting terminal connected to the common wiring and an inverting terminal and an output terminal connected to each other; It may include a compensation voltage calculation unit connected to the output terminal.

The data driver may include a driving integrated circuit (D-IC), and the control switch, the operational amplifier, and the compensation voltage calculator may be embedded in the driving integrated circuit.

The compensation unit may further include an analog-to-digital converter connected between the operational amplifier and the compensation voltage calculator.

The operational amplifier receives and amplifies the voltage variation, and the compensation voltage calculating unit multiplies the output voltage Vop of the operational amplifier by a first gain G1 and divides it by a second gain G2 to compensate the voltage. (CV) may be calculated (CV = Vop * (G1 / G2)) and supplied to the common voltage supply unit.

In addition, when the control switch cuts off the connection between the common wiring and the common voltage supply unit, the common wiring is floated, the thin film transistor is turned on and then turned off, and the data signal may be 0V.

The compensator may generate the compensated common voltage when driving of the liquid crystal display is started or when screen optimization is selected in a menu.

Meanwhile, the present invention provides a method of driving a liquid crystal display device including a thin film transistor, a storage capacitor having one electrode connected to the thin film transistor, and a liquid crystal panel having a liquid crystal capacitor, wherein the other electrode of the storage capacitor and the liquid crystal capacitor is floated. Turning the thin film transistor on and off while applying a 0 V data signal to the source electrode of the thin film transistor; Measuring a voltage variation of the other electrode of the storage capacitor and the liquid crystal capacitor; And generating a common voltage compensated by the voltage variation and supplying the common voltage to the other electrode of the storage capacitor and the liquid crystal capacitor.

The generating of the compensated common voltage using the voltage variation may include amplifying the voltage variation; Calculating a compensation voltage (CV) by multiplying the amplified voltage variation (Vop) by a first gain (G1) and dividing by a second gain (G2) (CV = Vop * (G1 / G2)); And generating the compensated common voltage using the compensation voltage.

The generating of the compensated common voltage using the voltage variation amount may further include converting the amplified voltage variation amount into digital data.

The amplified voltage variation may be converted into 7-bit digital data, the first and second gains may be 4-bit digital data, and the compensation voltage may be 7-bit digital data.

As described above, in the liquid crystal display device according to the present invention, the current pixel voltage fluctuation of the liquid crystal display device is measured, the optimum common voltage is calculated from the measured pixel voltage fluctuation amount, and applied to the liquid crystal display device. It is possible to automatically compensate for variations in flicker characteristics of the liquid crystal display.

In addition, by automatically compensating for the flicker characteristics when the LCD is initialized or when the screen is optimized by the user's selection, the flicker characteristics of the LCD may be improved to improve image quality.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

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

As shown in FIG. 5, the liquid crystal display 110 according to the exemplary embodiment of the present invention includes a liquid crystal panel 120 displaying an image and a gate driver 130 supplying a gate signal to the liquid crystal panel 120. And a data driver 140 supplying a data signal and a common voltage to the liquid crystal panel 120, a gate control signal to the gate driver 130, and an RGB signal and a data control signal to the data driver 140. The timing controller 150 is included.

In the liquid crystal panel 120, a plurality of gate lines GL1 to GLm and a plurality of data lines DL1 to DLn defining pixel regions P are formed to cross each other, and gate lines and gate lines are formed in each pixel region P. FIG. The thin film transistor T connected to the data line, the storage capacitor Cst and the liquid crystal capacitor Clc connected to the thin film transistor T are formed.

The liquid crystal panel 120 includes a plurality of common wires CL1 to CLn spaced apart from each other in parallel with the plurality of data wires DL1 to DLn. In another embodiment, a plurality of common wires CL1 to CLn are formed. May be formed to be spaced apart in parallel to the gate lines GL1 to GLm of the gate lines, or may be formed in a mesh shape parallel to the plurality of gate lines GL1 to GLm and the plurality of data lines DL1 to DLn. In an example, the feedback lines connected to the plurality of common lines CL1 to CLn may be separately formed at edge portions of the liquid crystal panel 120.

The common lines CL1 to CLn are connected to the storage capacitor Cst and the liquid crystal capacitor Clc.

The thin film transistor T is sequentially turned on in response to gate signals supplied from the gate driver 130 through the gate lines GL1 to GLm, and a plurality of data from the data driver 140. The data signal supplied through the wirings DL1 to DLn is applied to one electrode of the storage capacitor Cst and the liquid crystal capacitor Clc.

In this case, a common voltage supplied from the data driver 140 through the plurality of common lines CL1 to CLn is applied to the other electrodes of the storage capacitor Cst and the liquid crystal capacitor Clc.

The gate driver 130 and the data driver 140 each include a plurality of driving integrated circuits (D-ICs) and printed circuit boards (PCBs) on which the plurality of driving integrated circuits are mounted. can do.

In another embodiment, the gate driver 130 and the data driver 140 may be integrated to generate a gate signal and a data signal from one driver and supply the gate signal and the data signal to the liquid crystal panel 120. In another embodiment, the shift register may include a shift register. A portion of the gate driver, such as a register, may be formed in the liquid crystal panel 120 to generate a gate signal, and one driver may generate a data signal and supply the data signal to the liquid crystal panel 120.

In addition, the timing controller 150 receives a video signal, a data enable signal DE, a horizontal sync signal HSY, a vertical sync signal VSY, and a clock signal CLK from an external system, and receives a gate control signal and an RGB signal. A signal and a data control signal are generated and supplied to the gate driver 130 and the data driver 140.

In the liquid crystal display 110, when the user starts driving the liquid crystal display 110 or selects screen optimization from a menu, the timing controller 150 generates a compensation control signal to generate a gate driver ( 120 and the data driver 130, and the gate driver 120 and the data driver 130 generate a gate signal and a data signal corresponding to the compensation control signal and supply the same to the liquid crystal panel 120.

The compensator 160 of the data driver 140 measures the pixel voltage variation according to the compensation control signal, calculates a compensated common voltage corresponding to the measured pixel voltage variation, and applies the new common voltage to the liquid crystal panel 120. By supplying, a variation in flicker characteristics according to the temperature of the liquid crystal display 110 is compensated for.

The configuration and operation of the compensation unit 160 will be described with reference to the drawings.

6 is a diagram illustrating a compensating unit of a liquid crystal display according to an exemplary embodiment of the present invention, and FIGS. 7A, 7B, and 7C are diagrams illustrating a driving method of a liquid crystal display for compensating for variation in flicker characteristics according to an exemplary embodiment of the present invention. Figure is a diagram.

As illustrated in FIG. 6, the compensator 160 includes a common voltage supply unit 162, a control switch 164, an operational amplifier 166, and a compensation voltage calculator 168.

The common voltage supply unit 162 supplies a common voltage Vcom to the liquid crystal panel 120 of FIG. 5. For example, the common voltage supply unit 162 is mounted on a printed circuit board of the data driver 140 of FIG. 5 to supply power to the liquid crystal display. It may be a power integrated circuit for supplying.

The control switch 164 is disposed between the common voltage supply unit 162 and the plurality of common wirings (CL1 to CLn of FIG. 5) of the liquid crystal panel 120 to be common according to the compensation control signal of the timing controller (150 of FIG. 5). The voltage supply unit 162 and a plurality of common lines CL1 to CLn are connected or cut off.

That is, when the control switch 164 cuts off the connection between the common voltage supply unit 162 and the plurality of common lines CL1 to CLn according to the compensation control signal, the plurality of common lines CL1 to CLn are floating. In addition, the electrodes of the storage capacitor Cst and the liquid crystal capacitor Clc connected to the common lines CL1 to CLn are also floated.

In addition, when the control switch 164 connects the common voltage supply unit 162 and the plurality of common wirings CL1 to CLn according to the compensation control signal, the common voltages output from the common voltage supply unit 162 have a plurality of common wirings CL1. To CLn).

The non-inverting terminal (+) of the operational amplifier (OP AMP) 166 is connected to a plurality of common lines CL1 to CLn, and the inverting terminal (-) of the operational amplifier 166 is connected to the output terminal of the operational amplifier 166. The output terminal of the operational amplifier 166 is connected to the compensation voltage calculator 168.

Therefore, the operational amplifier 166 receives the amplification amount of the pixel voltage through the floated common lines CL1 to CLn and amplifies the pixel voltage variation to output to the compensation voltage calculator 168.

The compensation voltage calculator 168 calculates a compensation voltage CV corresponding to the output voltage of the operational amplifier 166 and supplies the compensation voltage CV to the common voltage supply unit 162. The corresponding compensation voltage CV is calculated, and a detailed method thereof will be described later.

The common voltage supply unit 162 sets the compensated common voltage Vcom using the compensation voltage CV and supplies the same to the liquid crystal panel 120. In this case, the control switch 164 is common according to the compensation control signal. The voltage supply unit 162 is connected to the common lines CL1 to CLn.

The control switch 164, the operational amplifier 166, and the compensation voltage calculator 168 of the compensation unit 160 may be embedded in the driving integrated circuit D-IC of the data driver 140 of FIG. 5. In this case, an analog-digital converter (ADC) for converting the measured analog voltage into a digital voltage may be added for data processing efficiency in the driving integrated circuit.

In this case, in order to measure the pixel voltage variation (ΔVp = Vkb + Vlk) of the kickback voltage and the leakage voltage of the current state of the liquid crystal panel 120 using the voltages of the plurality of common lines CL1 to CLn, As shown, the control switch 164 is turned off according to the compensation control signal to block the common voltage supply unit 162 and the plurality of common wirings CL1 to CLn.

Therefore, the capacitor voltage Vc, which is the voltage of the storage capacitor Cst and the other electrode of the liquid crystal capacitor Clc connected to the plurality of common lines CL1 to CLn, becomes floating.

At the same time, according to the compensation control signal, the gate driver 130 sequentially supplies the gate signal Vg of the high level voltage Vgh to the gate electrode of the thin film transistor T through the plurality of gate lines GL1 to GLm. The thin film transistor T is turned on and the data driver 140 supplies a 0 V data signal Vd to the source electrode of the thin film transistor T through the plurality of data lines DL1 to DLn.

Accordingly, the pixel voltage Vp, which is a voltage of one electrode of the storage capacitor Cst and the liquid crystal capacitor Clc connected to the plurality of common lines CL1 to CLn, becomes OV.

Subsequently, as shown in FIG. 7B, at the time when the gate signal Vg changes from the high level voltage Vgh to the low level voltage Vgl, the pixel is changed by the variation amount DVg = Vgh-Vgl of the gate signal Vg. The voltage Vp decreases by the kickback voltage Vkb at 0V, and then increases by the leakage voltage Vlk due to the off current of the thin film transistor T, so that the pixel voltage Vp is a negative pixel voltage variation amount (-DVp). )

However, as shown in FIG. 7C, since the common lines CL1 to CLn connected to the other electrodes of the storage capacitor Cst and the liquid crystal capacitor Clc are floating, the storage capacitor Cst and As the pixel voltage Vp of one electrode of the liquid crystal capacitor Clc changes, the storage capacitor Cst and the capacitor voltage Vc of the other electrode of the liquid crystal capacitor Clc also change.

Therefore, the capacitor voltage Vc also becomes the negative pixel voltage variation amount -Dpp. (Vc = -DVp)

That is, as the gate signal Vg is changed from the high level voltage Vgh to the low level voltage Vgl, the voltages of the common lines CL1 to CLn become negative pixel voltage variations (-DVp), The negative pixel voltage variation (-DVp) is input to the operational amplifier 166 of the compensator 160 and amplified, and the amplified negative pixel voltage variation amount (-DVp) is transferred to the compensation voltage calculator 168 and amplified. The compensation voltage CV corresponding to the negative pixel voltage variation (-DVp) is output, and the output compensation voltage CV is transferred to the common voltage supply unit 162 to be used for setting the compensated common voltage Vcom. The compensated common voltage Vcom is supplied to the liquid crystal panel 120.

At this time, in order to supply the compensated common voltage Vcom to the liquid crystal panel 120, the control switch 164 is turned on according to the compensation control signal, so that the common voltage supplying unit 162 and the plurality of common wirings CL1 to 162 are provided. CLn) is connected.

Here, a method of calculating the compensation voltage CV corresponding to the negative pixel voltage variation amount -DVp amplified using the gain in the compensation voltage calculator 168 will be described with reference to the drawings.

8 is a view for explaining a compensation voltage calculation method of a liquid crystal display according to an exemplary embodiment of the present invention, which will be described with reference to FIGS. 5 and 6.

As shown in FIG. 8, in the liquid crystal display device, the negative pixel voltage variation (-DVp) increases linearly with the driving time at high temperature, and as a result, the negative pixel voltage variation (-DVp) with the high temperature driving time. The absolute value of the output voltage (Vop) of the operational amplifier 166 amplified) increases linearly.

The compensation voltage calculator 168 may set the output voltage Vo of the operational amplifier 166 as the compensation voltage CV and output the same to the common voltage supply unit 162. 164, the operational amplifier 164, and the compensation voltage calculator 168 are embedded in the driving integrated circuit D-IC of the data driver 140, and one driving integrated circuit D-IC is used in various driving conditions. Since it should be applied to the liquid crystal display of, the gain may be defined such that the compensation voltage CV calculated from the output voltage Vo of the operational amplifier 166 has a predetermined range.

That is, the minimum compensation voltage straight line and the maximum compensation voltage straight line may be set above and below the output voltage straight line of the operational amplifier 166 of FIG. 8, and the compensation voltage CV output by the compensation voltage calculator 168 is the minimum compensation. The first and second gains G1 and G2 may be set to be between the voltage and the maximum compensation voltage.

Here, the minimum and the maximum means to compare the magnitude of the absolute value of the compensation voltage.

For example, the compensation voltage calculator 168 may output a value obtained by multiplying the output voltage Vop of the operational amplifier 166 by the first gain and dividing the second gain by the compensation voltage CV. (CV = Vop * (G1 / G2))

Specifically, when the output voltage Vop of the operational amplifier 166 is -1.8V and the minimum and maximum compensation voltages are -0.9V and -3.6V, respectively, the first and second gains G1 and G2 are respectively 0.3. And 0.42, the compensation voltage calculator 168 may output -1.28V between the minimum and maximum compensation voltages as the compensation voltage CV.

When the control switch 164, the operational amplifier 164, and the compensation voltage calculator 168 of the compensator 160 are incorporated in the driving integrated circuit D-IC of the data driver 140, efficient data processing is performed. For this purpose, an analog-to-digital converter (ADC) may be added between the output terminal of the operational amplifier 164 and the compensation voltage calculator 168. In this case, the analog-to-digital converter (ADC) may output the output of the operational amplifier 164. The analog voltage may be converted into a digital voltage, and the compensation voltage calculator 168 may read the converted digital voltage to output the compensation voltage CV as a digital voltage.

Table 1 illustrates a 7-bit digital code obtained by dividing the output voltage (Vop) of the operational amplifier 166 in the range of -0.3V to -2.5V by 0.02V intervals, and Table 2 shows the compensation voltage calculating unit 168. Table 4 illustrates a 4-bit digital code of first and second gains used in Table 3, and Table 3 sets the first and second gains G1 and G2 to 0.3 and 0.42, respectively, so that the compensation voltage calculator 168 This table shows a 7-bit digital code of the calculated compensation voltage (CV).

As shown in Tables 1 to 3, the analog-to-digital converter (ADC) converts the output analog voltage of the operational amplifier 164 into a 7-bit digital voltage, and the compensation voltage calculating unit 168 is 4 bits. The 7-bit compensation voltage CV may be output using the first and second gains G1 and G2.

TABLE 1

TABLE 2

[Table 3]

9 is a view for explaining the effect of compensating the flicker characteristic fluctuation of the liquid crystal display according to the exemplary embodiment of the present invention.

As shown in FIG. 9, the liquid crystal display (Sample 1 to Sample 10) according to the embodiment of the present invention had a flicker characteristic of about 5% at the initial stage of liquid crystal display immediately after completion of manufacture, but at high temperature for reliability test. The flicker characteristics of the liquid crystal display after driving deteriorated about 10% to about 20%.

However, the flicker characteristic of the liquid crystal display device after compensating for the flicker characteristic variation by measuring the pixel voltage variation DVp and calculating the compensation voltage is improved to about 5% to about 10%.

That is, in the liquid crystal display according to the exemplary embodiment of the present invention, the flicker characteristic is improved and the image quality is improved by measuring the current pixel voltage variation DVp and applying the compensated common voltage calculated therefrom to the liquid crystal display.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

1 is a view of one pixel of a conventional active matrix liquid crystal display device;

2 is a waveform diagram showing a gate signal and a pixel voltage of a conventional active matrix liquid crystal display device.

3A and 3B illustrate changes in flicker characteristics according to temperature of a conventional liquid crystal display device, respectively.

4 is a diagram illustrating a change in off current characteristics according to a temperature of a thin film transistor of a conventional liquid crystal display.

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

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

7A, 7B, and 7C illustrate a method of driving a liquid crystal display for compensating for variation in flicker characteristics according to an exemplary embodiment of the present invention.

8 is a view for explaining a method of calculating a compensation voltage of a liquid crystal display according to an exemplary embodiment of the present invention.

9 is a view for explaining the effect of compensating the flicker characteristic fluctuation of the liquid crystal display according to the exemplary embodiment of the present invention.

Claims (11)

A liquid crystal panel including gate wirings, data wirings and common wirings crossing each other, a thin film transistor connected to the gate wiring and data wiring, a storage capacitor and a liquid crystal capacitor connected to the thin film transistor and the common wiring; A gate driver supplying a gate signal to the gate wiring; A data driver supplying a data signal to the data line; A timing controller supplying a gate control signal to the gate driver and supplying an RGB signal and a data control signal to the data driver; Compensation unit for generating a common voltage compensated using the voltage variation measured from the common wiring to supply to the common wiring Liquid crystal display comprising a. The method of claim 1, The compensation unit, A common voltage supply unit supplying a common voltage to the common wiring; A control switch controlling the connection of the common voltage supply unit and the common wiring; An operational amplifier including a non-inverting terminal connected to the common wiring and an inverting terminal and an output terminal connected to each other; Compensation voltage calculation unit connected to the output terminal Liquid crystal display comprising a. The method of claim 2, And the data driver includes a driving integrated circuit (D-IC), and the control switch, the operational amplifier, and the compensation voltage calculator are included in the driving integrated circuit. The method of claim 3, wherein The compensator further comprises an analog-to-digital converter connected between the operational amplifier and the compensating voltage calculator. The method of claim 2, The operational amplifier receives and amplifies the voltage fluctuation amount, and outputs the amplified voltage. ) Is supplied to the common voltage supply unit by calculating (CV = Vop * (G1 / G2)). The method of claim 2, And when the control switch cuts off the connection between the common line and the common voltage supply unit, the common line is floated, the thin film transistor is turned on after being turned on, and the data signal is 0V. The method of claim 1, And the compensator generates the compensated common voltage when driving of the liquid crystal display is started or when screen optimization is selected in a menu. A driving method of a liquid crystal display device comprising a thin film transistor, a storage capacitor having one electrode connected to the thin film transistor, and a liquid crystal panel on which a liquid crystal capacitor is formed. Turning on and off the thin film transistor while applying the 0 V data signal to the source electrode of the thin film transistor while the other electrodes of the storage capacitor and the liquid crystal capacitor are floating; Measuring a voltage variation of the other electrode of the storage capacitor and the liquid crystal capacitor; Generating a common voltage compensated using the voltage variation and supplying the common voltage to the other electrode of the storage capacitor and the liquid crystal capacitor Method of driving a liquid crystal display device comprising a. The method of claim 8, Generating the compensated common voltage using the voltage variation amount, Amplifying the voltage variation; Calculating a compensation voltage (CV) by multiplying the amplified voltage variation (Vop) by a first gain (G1) and dividing by a second gain (G2) (CV = Vop * (G1 / G2)); Generating the compensated common voltage using the compensation voltage Method of driving a liquid crystal display device comprising a. The method of claim 9, The generating of the compensated common voltage using the voltage variation amount may further include converting the amplified voltage variation amount into digital data. 11. The method of claim 10, Wherein the amplified voltage variation is converted into 7-bit digital data, the first and second gains are 4-bit digital data, and the compensation voltage is 7-bit digital data.

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