KR100438966B1 - A liquid crystal display device applying common voltage having different phase and a method of operating thereof - Google Patents

Abstract

The liquid crystal display device of the present invention is for preventing signal retention due to residual voltage and wiring resistance and parasitic capacitance caused by a DC component of a common voltage. M gate lines and n data lines are vertically and horizontally arranged to provide n × m pixels. A thin film transistor is disposed in each pixel and is switched as the gate signal is input through the gate line. The liquid crystal panel applies a data signal input through the data line to the pixel electrode in the pixel. A gate driver circuit and a data driver circuit which are provided to supply the gate signal and the data signal to the gate line and the data line, respectively, and are provided outside the liquid crystal panel and connected to the data line D1 of the first column of the n data lines. Phase difference of 180 ° and different true values are respectively applied to the common electrode of the pixel connected to the common electrode and the data line Dn of the nth column. A common alternating current voltage having the same time is composed of the common electrode drive circuit for applying.

Description

A liquid crystal display device and a method of driving the liquid crystal display device to which a common voltage having a different phase is applied.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and in particular, to a common electrode of a pixel connected to a data line of a first column and a common electrode of a pixel connected to a data line of a last column by applying a common voltage having a different amplitude and having a 180 ° phase difference, The present invention relates to a liquid crystal display device and a liquid crystal display device driving method capable of eliminating residual DC components and preventing signal delay.

Liquid crystal display devices are transmissive flat panel displays, and are widely applied to various electronic devices such as mobile phones, PDAs, and notebook computers. Such LCDs are currently being practically used in comparison with other flat panel displays in that they can be made light and small and have high image quality. Moreover, as the demand for digital TVs, high-definition TVs, and wall-mounted TVs increases, studies on large-area LCDs applicable to TVs are being actively conducted.

In general, LCDs can be divided into several methods depending on how the liquid crystal molecules are operated. However, active matrix thin film transistor LCDs are mainly used in terms of fast reaction speed and low afterimage. It is used.

The structure of the panel 1 of the TFT LCD is shown in FIG. As shown in the drawing, the liquid crystal panel 1 is formed with a plurality of gate lines 3 and data lines 5 arranged vertically and horizontally to define a plurality of pixels. In each pixel, a thin film transistor 6, which is a switching element, is disposed, and when a scan signal is input through the gate line 3, the signal is switched and input through the data line 5 to the liquid crystal layer 9. ) Is applied. In the figure, reference numeral Cst denotes an accumulation capacitor which serves to hold the data signal until the next scanning signal is applied, and C _LC denotes a capacitor formed by the liquid crystal layer 9.

2 is a cross-sectional view showing in detail the structure of one pixel of the liquid crystal display device configured as described above. As shown in the figure, the liquid crystal display device is laminated on the entire gate electrode 22 formed on the lower substrate 20 made of a transparent insulating material such as glass, and the entire substrate 20 on which the gate electrode 22 is formed. The gate insulating layer 24, the semiconductor layer 26 formed on the gate insulating layer 24, and the source / drain electrodes 28 formed on the semiconductor layer 26. Meanwhile, a pixel electrode 30 made of a transparent metal such as indium tin oxide (ITO) is formed in the image display area of the pixel, and is electrically connected to the source / drain electrode 28, and a passivation layer thereon. ; 32) are laminated.

In addition, a black matrix 42, which is a light blocking layer, is formed on the upper substrate 40 to prevent light leakage from the image non-display area of the pixel, that is, between the pixel and the pixel and the TFT area. In the display area, a color filter layer 44 for real color is formed. The common electrode 13 made of a transparent metal such as ITO is formed on the black matrix 42 and the color filter layer 44.

As described above, a spacer 52 is positioned between the lower substrate 20 on which the thin film transistor is formed and the upper substrate 40 on which the color filter layer 44 is formed to maintain a constant cell gap therebetween. The liquid crystal is injected to form a liquid crystal layer 50, and the liquid crystal display device is completed by sealing and bonding the lower substrate 20 and the upper substrate 40.

Although not shown in the drawings, an alignment layer for orienting liquid crystal molecules of the liquid crystal layer 50 is laminated on the protective layer 32 of the lower substrate 20 and the common electrode 46 of the upper substrate 40. have.

The gate driver IC 15, the data driver IC 16, and the common electrode driver circuit 17 as shown in FIG. 1 are mounted outside the liquid crystal panel 1 configured as described above, respectively. A signal is applied to the data line 5 and the common electrode 13. As the scan signal is input to the liquid crystal panel 1 from the external gate driver IC 16 through the gate line 3, the semiconductor layer 26 is activated to form a channel layer in the TFT 6, and at the same time, The data signal applied from the driving circuit 16 to the data line 5 is applied to the liquid crystal layer 50 through the channel layer.

Although not illustrated, the gate line 3 and the data line 5 are formed on the lower substrate, while the common electrode 13 is formed on the upper substrate. Therefore, in order to apply the common electrode signal input through the pad of the lower substrate to the common electrode 13, a means for electrically connecting the upper substrate and the lower substrate is required. Typically, the electrical connection between the upper substrate and the lower substrate is made by applying Ag paste to the outer substrate on the lower substrate and then connecting the Ag paste to the pad of the common electrode formed on the upper substrate.

3 illustrates a gate signal Vg and a data signal Vd applied to the liquid crystal panel 1 from the gate driver IC 15 and the data driver IC 16. As shown in Fig. 3A, as the voltage Vg of the frequency set to the gate electrode 22 of the TFT 6 is applied, the semiconductor layer of the TFT 6 is activated to provide a source / The voltage Vd shown in FIG. 3B is applied to the pixel electrode 30 of the liquid crystal panel 1 through the drain electrode 28, and the common voltage Vcom is applied to the common electrode 13. . Therefore, the liquid crystal panel 1 receives a voltage corresponding to the difference (| Vd-Vcom |) of the voltage applied to the pixel electrode 30 and the common electrode 13. On the other hand, as shown in the figure, the data signal applied to the pixel electrode 30 is inverted phase of the positive polarity (+) and the negative polarity (-) around the common electrode signal for each frame. As such, the reason for applying the data signal to the data line by reversing the phase with respect to the common electrode signal is that the liquid crystal is deteriorated when the same voltage is continuously applied between the pixel electrode and the common electrode. This is to prevent crosstalk on the screen.

However, even when the phase-inverted data signal is applied to each frame as described above, since the DC voltage is applied to the common electrode 13 of the liquid crystal panel 1, the liquid crystal layer 50 maintains the DC voltage component. As a result, afterimages appear on the screen when the liquid crystal panel 1 is driven for a long time.

In addition, although the same voltage Vcom is formed over the entire panel 1 in the common electrode 13 to which the common voltage Vcom is applied, in the actual liquid crystal panel 1, an Ag paste formed on one side of the outer substrate of the lower substrate. Since the voltage (Vcom) is applied to the common electrode terminal portion of the upper substrate through the signal is transmitted to the opposite side, the signal transmission by the parasitic capacitance generated between the wiring resistance and the electrodes present in the common electrode 13 There will be a delay. Therefore, the amount of charges charged in the pixels formed in the entire liquid crystal panel 1 is different. In other words, in the liquid crystal panel 1 shown in FIG. 1, different amounts of charge are charged in the pixels connected to the data line D1 in the first column and the pixels connected to the data line Dn in the last column. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and includes a common electrode of a pixel connected to a data line of a first column among a plurality of pixels defined by m gate lines and n data lines and a pixel connected to a data line of an nth column. A liquid crystal display device and a driving method thereof capable of simultaneously eliminating the DC component remaining in the liquid crystal layer and preventing signal delay due to wiring resistance and parasitic capacitance by simultaneously applying a common voltage having a 180 ° phase difference and different amplitude to each electrode. The purpose is to provide.

In order to achieve the above object, in the liquid crystal display device according to the present invention, m gate lines and n data lines are vertically and horizontally arranged to define n × m pixel regions, and a thin film transistor is disposed in each pixel to form the gate. A liquid crystal panel which is switched as a gate signal is input through a line and applies a data signal input through the data line to a pixel electrode in a pixel; and a gate signal provided to the gate line and the data line, respectively, which is installed outside the liquid crystal panel. And a gate driver circuit and a data driver circuit for supplying a data signal, and a common electrode of a pixel which is provided outside the liquid crystal panel and connected to the data line D1 of the first column of the n data lines, and the data line Dn of the nth column. Are simultaneously applied to an AC common voltage having a phase difference of 180 ° and a different amplitude to the common electrode of the pixel connected to It is composed of a common electrode driving circuit.

In addition, the driving method of the liquid crystal display device according to the present invention comprises the steps of switching the thin film transistor by applying a gate signal to the gate electrode of the thin film transistor through the m gate lines arranged in the liquid crystal panel, the thin film transistor is switched Therefore, the data signal is output to n data lines arranged in the liquid crystal panel and applied to the pixel electrode through the source / drain electrodes of the thin film transistor, and the alternating current is applied to the common electrode connected to the data lines of the first column arranged in the liquid crystal panel. The pixel electrode by applying a first common voltage and a second common voltage of an alternating current having a phase difference of 180 ° with the first common voltage to the common electrode connected to the data line of the nth column at the same time as the first common voltage It consists of driving a liquid crystal molecule by the voltage difference with and.

1 is a plan view showing the structure of a conventional liquid crystal display device.

FIG. 2 is a cross-sectional view illustrating a structure of a Han pixel of the liquid crystal display of FIG. 1. FIG.

3 is a signal waveform diagram of a conventional liquid crystal display device.

4 is a view showing the structure of a liquid crystal display device according to the present invention;

5 is a circuit diagram of a common electrode driving circuit.

6 is a signal waveform diagram of a liquid crystal display device according to the present invention;

7 is a schematic perspective view of a liquid crystal display device according to the present invention;

** Explanation of symbols for main parts of drawings **

101: liquid crystal panel 103: gate line

105: data line 106: thin film transistor

109: liquid crystal layer 113: common electrode

115: gate driver IC 116: data driver IC

117: common electrode driving circuit 123: operational amplifier

125: inverter 140: top panel

143: common electrode pad 150: lower panel

152 Ag paste

The present invention provides a liquid crystal display device in which an afterimage is removed and the same amount of charge is charged over the entire pixel of the liquid crystal panel. To this end, the present invention applies an alternating current voltage which is inverted in phase to the common electrode. In particular, in the present invention, two voltages having phase differences with each other are simultaneously applied to the common electrode of the pixel connected to the data line in the first column of the liquid crystal panel and the common electrode of the pixel connected to the data line in the last column, thereby providing wiring resistance and parasitics of the common electrode. Prevent signal delay due to capacitance.

Since the voltage applied to the common electrode formed in the pixels of the first column and the voltage applied to the common electrode of the last column are AC voltages having a phase difference of 180 ° with each other, the synthesized voltage is approximately 1/2 of the amplitude of the AC voltage. It will be DC voltage. However, at this time, by setting the amplitude of the voltage applied to the common electrode of the first column pixel and the voltage applied to the common electrode of the last column pixel differently, it is possible to apply an AC voltage to the entire common electrode of the liquid crystal panel. It is possible to prevent the liquid crystal layer from being affected by the common electrode signal of, thereby preventing afterimages.

Hereinafter, a liquid crystal display device according to the present invention will be described in detail with reference to the accompanying drawings.

4 is a view showing a liquid crystal display device according to the present invention. As shown in the drawing, the liquid crystal panel 101 has m gate lines 103 and n data lines 105 arranged vertically and horizontally to define n × m pixels. A thin film transistor 106 is disposed in each pixel, and when a scan signal is input through the gate line 103, the thin film transistor 106 is switched to apply a signal input through the data line 105 to the liquid crystal layer 109.

The gate line 103 is connected to a gate driver IC 115 mounted outside the panel 101 to receive a scan signal, and the data line 105 is connected to the data driver IC 116. In addition, a common electrode driving circuit 117 for applying a signal to the common electrode 113 of the liquid crystal panel 101 is provided outside the panel 101. Although not shown, the gate driver IC 115, the data driver IC 116, and the common electrode driver circuit 117 are connected to a controller. As a signal is input to the controller from an external host or the like, a power supply unit (not shown) supplies power to the gate driver IC 115, the data driver IC 116, and the common electrode driver circuit 117. The controller controls the gate driver IC 115, the data driver IC 116, and the common electrode driver circuit 117 to output a signal.

As shown in the figure, the common electrode driving circuit 117 has two output terminals A and B formed therein. The first output terminal A applies a signal to a common electrode of pixels connected to the first data line D1 of the n data lines 105 arranged on the liquid crystal panel 101, and the second output terminal B is A signal is applied to the common electrodes of the pixels connected to the last line Dn of the data line 105.

As described above, the data signal input to the data line D1 of the first column is transmitted to the data lines D2, D3 ... Dn of the next column and the data signal input through the data line Dn of the last nth column. Data lines Dn-1, Dn-2 ... D1 of the previous column are transmitted. Therefore, since the same size data signal is simultaneously input to the common electrode 113 of the pixel connected to the data line D1 of the first column and the data line Dn of the nth column, the signal by the wiring resistance or the parasitic resistance is applied. This can prevent delays.

In addition, the signal supplied from the common electrode driving circuit 117 is an AC signal. As shown in FIG. 6, the common electrode driving circuit 117 is shown in FIG. 6 (b) through the A terminal and the B terminal in synchronization with the gate voltage Vg applied to the gate electrode of the TFT 6. As described above, the AC voltages Vcom1 and Vcom2 are supplied. At this time, as shown in the figure, the common voltage Vcom1 output from the A terminal and the common voltage Vcom2 output from the B terminal have a phase difference of 180 ° with each other and their amplitudes are different. Although the amplitude (a) of the voltage (Vcom1) output from the terminal A is set smaller than the amplitude (b) of the voltage (Vcom2) output from the terminal B, the amplitude (a) of the Vcom1 is the amplitude (b) of the Vcom2. It may be set larger. As the common voltages Vcom1 and Vcom2 output from the A terminal and the B terminal are applied to the common electrode of the first row and the common electrode of the nth column through the A terminal and the B terminal, respectively, the first (the initial threshold time of supply) is applied first. AC voltage is applied to the common electrode of the column and the common electrode of the nth column, respectively, but as shown in FIG. 6 (c), as the time elapses, the average value of Vcom1 and Vcom2 over the entire pixel (c = (a + b) AC voltage Vcom3 having) / 2) is applied.

This average value eventually becomes the reference voltage of the data signal as a common voltage applied to the common electrode of the entire pixel. In this case, as shown in the figure, the common voltage becomes an AC voltage having an amplitude c. Since the amplitude c is much smaller than the amplitude of the data voltage Vd applied to the pixel electrode, it can be used as the reference voltage of the data voltage Vd even though the common voltage Vcom3 is an AC voltage. Of course, it may be more preferable to modify the amplitude of the data voltage Vd to correspond to the amplitude c of the AC voltage Vcom3.

As described above, in the present invention, an AC voltage having a different amplitude from the common electrode driving circuit 117 is connected to the common electrode of the pixel connected to the first column data line D1 of the liquid crystal panel and the data line Dn of the nth column. Since an alternating voltage having a small amplitude is applied to the common electrodes of all the pixels and applied to the common electrodes of all the pixels, it is possible to eliminate afterimages generated by applying a DC voltage to the common electrodes.

5 is a diagram showing the structure of a common electrode driving circuit 117 of the present invention. As shown in the figure, the common electrode driving circuit 117 is provided with two operational amplifiers 123a and 123b. A power supply voltage V _DD and a signal voltage V _{CAC are} respectively input to both terminals of the first operational amplifier 123a and the common voltage of Vcom1 is output through the terminal A.

On the other hand, the inverter 125 is connected to the front end of the second operational amplifier 123b, and the power supply voltage V _DD which is inverted in phase is input to the second operational amplifier 123b, and thus, the first operational amplifier 123a. The common voltage Vcom2 having a phase difference of 180 ° from the voltage Vcom1 output from the P1 is output through the terminal B. In this case, since the variable resistors VR1 and VR2 having different values are connected to the power supply voltage V _DD input to the first operational amplifier 123a and the second operational amplifier 123b, the variable resistor By adjusting (VR1, VR2) it is possible to adjust the amplitude of the output common voltage (Vcom1, Vcom2), it is possible to control the amplitude of the AC voltage applied to the common electrode of the entire panel.

The common electrode driving circuit 117 is configured as one driving circuit as described above, and is connected to the common electrode of the pixel connected to the data line of the first column and the data line of the nth column by a inverter by using a common voltage having a different phase difference from each other. Although each may be supplied to the common electrode of the pixel, the common electrode driving circuit 117 may be composed of two circuits each outputting signals having different phase differences. In this case, the two common electrode driving circuits are controlled by a controller (not shown) to apply signals having different phases and amplitudes to the common electrode.

FIG. 7 is a schematic perspective view of a liquid crystal display device manufactured according to the present invention, and illustrates a schematic shape for applying an actual signal from the common electrode driving circuit 117 to the common electrode. The common electrode driving circuit 117 is connected to the lower panel 150 of the liquid crystal display device similarly to the gate driving IC and the data driving IC. Therefore, in order to apply the common voltage Vcom to the common electrode formed on the upper panel 140, Ag pastes 152 connected to each other by electrical links are coated on the outer portion of the lower panel 150. 152 is electrically connected to the common electrode pad (or terminal) 143 formed on the upper panel 140 to apply a voltage Vcom to the common electrode. In particular, in the present invention, since the common voltage Vcom output from the A and B terminals of the common electrode driving circuit 117 is simultaneously applied to the common electrode of the first column and the common electrode of the last column arranged in the liquid crystal panel, they are common to the first column. Ag paste 152 for applying the voltage Vcom and Ag paste 152 for applying the common voltage Vcom to the last column are formed on both sides of the lower panel 150, and the Ag paste on each side is common. It is connected to the A terminal and the B terminal of the electrode drive circuit 117.

As described above, in the present invention, since the common voltage is simultaneously applied to the common electrode of the pixel connected to the data line of the first column of the liquid crystal panel and the common electrode of the pixel connected to the data line of the last column, the wiring resistance and the parasitic capacitance Signal delay can be prevented. In addition, in the present invention, a residual voltage caused by a DC voltage component can be effectively removed by applying a common voltage having a phase difference of 180 ° and a different amplitude to the common electrode of the first column and the common electrode of the last column.

Claims (10)

m gate lines and n data lines are arranged horizontally and horizontally to define n × m pixel regions, and thin film transistors are disposed in each pixel, and are switched as the gate signal is input through the gate lines, A liquid crystal panel which applies an input data signal to a pixel electrode in the pixel; A gate driver circuit and a data driver circuit provided outside the liquid crystal panel to supply a gate signal and a data signal to the gate line and the data line, respectively; And 180 ° phase difference between the common electrode of the pixel connected to the data line D1 of the first column and the common electrode of the pixel connected to the n-th data line Dn of the n data lines A liquid crystal display device comprising a common electrode driving circuit for simultaneously applying alternating current common voltage. The method of claim 1, wherein the thin film transistor, Board; A gate electrode formed on the substrate; A gate insulating layer stacked over the entire substrate on which the gate electrode is formed; A semiconductor layer formed on the gate insulating layer; A source / drain electrode formed on the semiconductor layer; And And a protective layer laminated over the entire substrate. The amplitude (b) of the AC voltage applied to the common electrode of the pixel connected to the data line of the first column and the amplitude (b) of the AC voltage applied to the common electrode of the pixel connected to the data line of the nth column. ) Is different from the liquid crystal display device. 4. The liquid crystal display device according to claim 3, wherein the voltage applied to the common electrode of the entire liquid crystal panel is an alternating voltage having an amplitude of c = | (a + b) / 2 |. The method of claim 1, wherein the common electrode driving circuit, A first operational amplifier configured to output a first common voltage by receiving a signal voltage and a power supply voltage; A second operational amplifier provided with an inverter installed at a front end thereof, and outputting a second common voltage by receiving a phase-inverted signal voltage and a power supply voltage; And And a first variable resistor and a second variable resistor connected to the input terminals of the first operational amplifier and the second operational amplifier to adjust the resistance of the input voltage. The method of claim 1, wherein the common electrode driving circuit, A first common electrode driving circuit disposed outside the liquid crystal panel and applying a first common voltage to a common electrode connected to the data lines of the first column; And And a second common electrode driving circuit disposed outside the liquid crystal panel and applying a second common voltage different in phase and amplitude from the first common voltage to the common electrode connected to the data lines of the nth column. Display element. The common electrode and n-th column of data of claim 1, wherein the common voltages formed on both outer sides of the liquid crystal panel are connected to the common electrode driving circuit, and the common voltages output from the common electrode driving circuit are connected to the data lines of the first column. And an Ag paste each applied to a common electrode connected to the line. Switching the thin film transistor by applying a gate signal to a gate electrode of the thin film transistor through m gate lines arranged in the liquid crystal panel; Outputting a data signal to n data lines of a liquid crystal panel as the thin film transistor is switched and applying the data signal to a pixel electrode through a source / drain electrode of the thin film transistor; And The first common voltage of the alternating current is applied to the common electrode connected to the data lines of the first column arranged in the liquid crystal panel, and the alternating current has a phase difference of 180 ° from the first common voltage to the common electrode connected to the data line of the nth column. And applying a second common voltage simultaneously with the first common voltage to drive the liquid crystal molecules by a voltage difference from the pixel electrode. The method of claim 8, wherein the amplitude (a) of the first common voltage and the amplitude (b) of the second common voltage are different from each other. The liquid crystal display device according to claim 8, wherein the voltage applied to the common electrode of the entire liquid crystal panel is an AC voltage having an amplitude of c = | (a + b) / 2 |.