KR20010073557A - A common voltage generator - Google Patents

Abstract

PURPOSE: A common voltage generator is provided which, when different common voltages are applied to an LCD panel, reflects a component compensating the kick back voltage of voltage actually applied to pixels in the applied common voltages, to prevent generation of flicker. CONSTITUTION: A common voltage generator includes an LCD panel(300), a common voltage generating unit(100), a pixel-applied voltage detector(400), and an adder(200). The LCD panel has a plurality of thin film transistors having multiple gate lines, multiple data lines, gate electrodes connected to the gate lines and source electrodes connected to the data lines, pixel electrodes connected to the drain electrode of the thin film transistors, and common electrodes opposite to the pixel electrodes. The LCD panel further has a plurality of common contact points. The common voltage generating unit applies common voltages having the same level to the common contact points. The pixel-applied voltage detector detects voltages applied to predetermined pixels of the LCD panel for a specific frame and calculates the root-mean-square of the detected pixel-applied voltages. The adder adds the common voltages with the output voltages of the voltage detector to apply the added voltages to the common contact points.

Description

Common Voltage Generator {A COMMON VOLTAGE GENERATOR}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for a thin film transistor liquid crystal display (hereinafter, referred to as a TFT-LCD), and more particularly, an actual pixel reflecting a kickback voltage. The present invention relates to a common voltage generator of a liquid crystal display device in which a level of a common voltage is determined in consideration of a voltage.

The TFT-LCD is a display device that obtains a desired image signal by applying an electric field to a liquid crystal material having an anisotropic dielectric constant injected between two substrates, and controlling the amount of light transmitted through the substrate by adjusting the intensity of the electric field.

On the substrate of such a TFT-LCD, a plurality of gate lines parallel to each other and a plurality of data lines insulated from and intersecting the gate lines are formed, and an area surrounded by the gate lines and the data lines defines one pixel. TFTs are formed at portions where the gate lines and the data lines of each pixel cross each other.

In order to drive the TFT-LCD, the gate line is sequentially driven and at the same time, a data voltage to be applied to the source terminal of the TFT connected to the driving gate line is applied through the data line. At this time, in order to prevent deterioration of the liquid crystal generated as the electric field in the direction is continuously applied to the pixels formed in the TFT, the polarity of the data voltage is inverted with respect to the common voltage every frame. The TFT-LCD driving method for inverting the polarity of the data voltage is called an inversion driving method.

However, the gate line and the data line of the TFT-LCD have a resistance component and a parasitic capacitance component, which causes a delay of the gate and data voltages by the time constant determined by the product of these two values, resulting in a kickback voltage. This kickback voltage is a factor causing flicker. Here, the signal delay becomes larger as the size of the liquid crystal panel increases.

Therefore, in the related art, the signal delay is compensated by applying different common voltages to the LCD panel in consideration of the kickback voltage according to the signal delay of the gate line and the data line.

1 is a driving circuit diagram of a liquid crystal display device which applies different common voltages to a conventional LCD panel. As shown in FIG. 1, a driving circuit of a conventional liquid crystal display device applying different common voltages to an LCD panel includes resistors R1, R2, and R3 connected in series to an op amp AMP and a power supply voltage VDD. , R4, R5 and R6, resistor R7 connected to the contacts of resistors R3 and R4, capacitor C1 connected in parallel to resistor R7, and resistor R8 connected to the contacts of resistors R4 and R5. And a capacitor C2 connected in parallel to the resistor R8, a resistor R9 connected to the contacts of the resistors R5 and R6, a capacitor C3 connected in parallel to the resistor R9, and a resistor R6. It includes a common voltage regulator including a variable resistor (VR).

Here, the first common voltage Vcom1 is the voltage of the capacitor C1, the second common voltage Vcom2 is the voltage of the capacitor C2, and the third common voltage Vcom3 is the voltage of the capacitor C3.

Accordingly, as shown in FIG. 1, the voltage values of the capacitors C1, C2, and C3 are changed according to the characteristics of the panel and the kickback voltage, so that the voltage values of the capacitors C1, C2, and C3 are changed. By adjusting (Vcom1, Vcom2, Vcom3), the kickback voltage is compensated.

However, the conventional method as shown in FIG. 1 has a problem in that it is difficult to adjust the variable resistance every time according to the characteristics of the panel for each product, and there is a problem in that it cannot actively cope with the characteristics.

An object of the present invention is to prevent occurrence of flicker by applying a component that compensates a kickback voltage component of a voltage applied to an actual pixel to a common voltage applied to the LCD panel.

1 is a driving circuit diagram of a liquid crystal display device which applies different common voltages to a conventional LCD panel.

2 is a block diagram of a common voltage generator according to an exemplary embodiment of the present invention.

3 is a simplified view of an LCD panel state according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating an equivalent circuit for the pixel A portion of FIG. 3.

5 is a diagram illustrating a pixel application voltage detected by the A pixel.

6 is a view illustrating an adder according to an embodiment of the present invention.

According to an aspect of the present invention for achieving the above object, a common voltage is applied to a plurality of common electrode contact points formed in an LCD panel, and then a voltage applied to a predetermined pixel is detected. In this case, the predetermined pixel in which the voltage is detected is a pixel in which the kickback voltage is generated due to the delay of the gate line and the data line, and the number of the common electrode contact points is preferably equal to the number of contact points. The voltage detected by the predetermined pixel is preferably a root-mean-square of a voltage obtained by accumulating the difference (voltage applied to the pixel) between the common voltage and the data voltage.

Meanwhile, the present invention adds a common voltage applied to a panel and a voltage applied to a predetermined pixel, and applies the addition result to a plurality of common contact points.

As a result, the common voltage applied to each common electrode contact point is increased or decreased by the square root mean square of the pixel applied voltage in which the kickback voltage is reflected in the initial common voltage, and is applied to each common electrode contact point when the voltage applied to each of the specific pixels is different. The common voltage becomes different.

Therefore, the common voltage generating circuit according to the feature of the present invention,

A plurality of thin film transistors having a plurality of gate lines, a plurality of data lines, a gate electrode connected to the gate line and a source electrode connected to the data line, and a pixel electrode connected to a drain electrode of the thin film transistor, An LCD panel having a common electrode facing the pixel electrode and having a plurality of common contact points;

A common voltage generator configured to apply a common voltage having the same level to a plurality of common contact points formed on the LCD panel;

A pixel applied voltage detector for detecting a voltage applied to a predetermined pixel of the LCD panel during a specific frame and calculating and outputting a square root mean square of the detected pixel applied voltage; And

And an adder configured to add the common voltage of the common voltage generator and an output voltage of the pixel application voltage detector to the common contact point.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention.

2 is a block diagram of a common voltage generator according to an exemplary embodiment of the present invention. As shown in FIG. 2, a common voltage generator according to an exemplary embodiment of the present invention includes a common voltage generator 100, an adder 200, an LCD panel 300, and a pixel applied voltage detector 400.

Here, the common voltage generator 100 outputs a common level Vcom of a predetermined level to the LCD panel 300, and the LCD panel 300 is applied to a display panel of a general thin film transistor liquid crystal display. The degree of twist of the liquid crystal is varied according to the common voltage Vcom and a data voltage not shown to display a desired image.

Here, the LCD panel 300 will be described with reference to FIG. 3. The LCD panel 300 has three common contact points P1 receiving the common voltage Vcom output from the common voltage generator 100 as shown in FIG. 3. , P2, P3) are formed near the three corners of the panel. In addition, a display area 310 that is visible to a human eye is formed at the center of the panel.

In the TFT-LCD panel 300, the display area 310 is called a thin film transistor substrate and is formed on the substrate, and the plurality of gate lines G1, ..., Gn-1, Gn and the plurality of data lines D1, ..., orthogonal to Dn, Dn + 1, a plurality of gate lines G1, ..., Gn-1, Gn, and a plurality of data lines D1, ..., Dn, Dn + 1 It includes a plurality of pixels formed in and a TFT formed in the pixel. The common contact points P1, P2, and P3 are formed on a common substrate called an opposing substrate. In FIG. 3, the two substrates are represented as one so that the common voltage application point and the image display portion can be identified.

Referring to the display area 310 of FIG. 3, a plurality of pixels are driven by an inversion driving method. That is, the plurality of pixels have a polarity opposite to that of FIG. 3 if the polarity of the current frame is the same as that of FIG. 3.

Here, the operation of the plurality of pixels will be described with reference to FIG. 4 in which the pixels A are equivalently represented.

FIG. 4 is a diagram illustrating an equivalent circuit for the pixel A portion of FIG. 3. As shown in FIG. 4, the gate electrode g, the source electrode s, and the drain electrode d of the TFT 10 are connected to the gate line Gn, the data line Dm, and the pixel electrode P, respectively. The liquid crystal material is formed between the pixel electrode P and the common electrode Com, which is equivalently represented as the liquid crystal capacitor Clc. The storage capacitor Cst is formed between the pixel electrode and the front gate line Gn-1, and the parasitic capacitance Cgd is generated between the gate electrode and the drain electrode due to misalignment. The liquid crystal capacitor Ccl and the storage capacitor Cst act as loads that the TFT-LCD should drive.

Therefore, in the operation of the pixel A, when a gate-on voltage is applied to the gate electrode connected to the gate line Gn, the TFT 10 is turned on to become a conductive state, and at this time, the data voltage representing the image signal is the source electrode ( This data voltage is applied to the drain electrode d by applying through s). Then, the data voltage is applied to the liquid crystal capacitor Clc and the storage capacitor Cst through the pixel electrode P, respectively, and an electric field is formed by the voltage difference between the pixel electrode Cp and the common electrode Com.

By the way, when the TFT 10 is turned on, the voltage applied to the liquid crystal capacitor Clc and the storage capacitor Cst must continue to be maintained even after the TFT is turned off, but is formed by the delay of the gate line and the data line. Because of the parasitic capacitance Cgd, the voltage applied to the pixel electrode causes distortion. This distorted voltage is the kick-back voltage.

The kickback voltage ΔV at this time is obtained by the following equation (1).

Here, Vg denotes a change amount of the gate voltage, that is, a difference between the gate on voltage Von and the gate off voltage Voff.

This voltage distortion always acts in the direction of lowering the voltage of the pixel electrode regardless of the polarity of the data voltage, which is shown in FIG.

In Fig. 5, Vg, Vd, and Vp represent the gate voltage, the data voltage, and the voltage of the pixel electrode, respectively, and Vcom and ΔV represent the common electrode voltage (common voltage) and kickback voltage, respectively. Likewise, in an ideal TFT-LCD, when the gate voltage Vg is on, the data voltage Vd is applied to the pixel electrode to maintain the data voltage even when the gate voltage is turned off. As described above, in the portion where the gate voltage is changed, the pixel voltage Vp is lowered by the kickback voltage due to the kickback voltage ΔV.

Accordingly, the voltage Vp applied to the actual pixel represents a voltage including the kickback voltage component as shown in FIG. 5.

Meanwhile, as illustrated in FIG. 5, the pixel application voltage detector 400 detects an applied voltage that is actually a pixel affected by the kickback voltage. In this case, the pixel applying voltage detector 400 detects a voltage applied to the pixel of three points corresponding to three points where the common voltage Vcom is applied. The detected voltage is accumulated, and the average value thereof is calculated and output. That is, when the pixel A is one of the detected pixels, the pixel application voltage detector 400 detects and accumulates the voltage Vp applied to the actual pixel A hatched, and accumulates the square root mean square, Calculate the average of the cumulative values.

Here, it is easy for a person skilled in the art to detect the voltage applied to the three points (three) pixels as described above, or to detect the voltage applied to one pixel. At this time, the position of one pixel is preferably the center side of the panel.

The value detected by the pixel application voltage detector 400 is applied to the adder 200 and added with the common voltage Vcom. Here, the adder 200 includes three (210, 220, 230) corresponding to three pixels for which the actual pixel voltage is detected. However, only one adder is needed if the actual pixel applied voltage is detected in one pixel.

The adders 210, 220, 230 have the same configuration with each other, and the configuration is shown in FIG.

6 illustrates an adder according to an embodiment of the present invention, which is an adder 230 for generating a common voltage Vcom3 of a common electrode contact point P3. As shown in FIG. 6, the adder 230 according to an exemplary embodiment of the present invention is a non-inverting amplifier AMP, which is an output terminal of the pixel application voltage detector 400 and an output terminal of the common voltage generator 100 at the non-inverting terminal. This connection is connected to one end of the resistor Ra and one end of the resistor Rf which are grounded to the inverting terminal, and the output terminal is connected to the other end of the resistor Rf and the common electrode contact point P3.

Here, the pixel application voltage detector 400 outputs a voltage Vrms that is a root mean square relative to the voltage VA applied to the pixel A. FIG. Therefore, the voltage Vrms + Vcom, to which the voltage Vrms and the common voltage Vcom are added, is applied to the non-inverting terminal of the non-inverting amplifier AMP.

Therefore, the output of the non-inverting amplifier AMP is (1 + Rf / Ra) (Vrms + Vcom) is output, and the value of 1 + Rf / Ra is negligible so that Vrms + Vcom is the LCD panel 300 A common voltage Vcom3 is output to the common electrode contact point P3 of.

In the case of the adders 210 and 220, the kickback voltage may be changed according to the output of the pixel-applied voltage detection unit 400 of which the voltage applied to the pixels adjacent to the common electrode contact points P1 and P2 is similar to the adder 230. The common voltages Vcom1 and Vcom2 considering ΔV are applied to the common electrode contact points P1 and P2.

As mentioned above, although the Example of this invention was described, this invention is not limited to the said Example, Of course, many other changes and a deformation | transformation are possible.

As described above, according to the present invention, since it is not necessary to design a common voltage in consideration of the characteristics of the LCD panel in advance, the inconvenience of adjusting the variable resistance is eliminated. Then, the flicker phenomenon caused by the signal delay of the gate line and the data line can be prevented.

Claims (7)

A plurality of thin film transistors having a plurality of gate lines, a plurality of data lines, a gate electrode connected to the gate line and a source electrode connected to the data line, and a pixel electrode connected to a drain electrode of the thin film transistor, An LCD panel having a common electrode facing the pixel electrode and having a plurality of common contact points; A common voltage generator configured to apply a common voltage having the same level to a plurality of common contact points formed on the LCD panel; A pixel applied voltage detector for detecting a voltage applied to a predetermined pixel of the LCD panel during a specific frame and calculating and outputting a square root mean square of the detected pixel applied voltage; And And an adder configured to add a common voltage of the common voltage generator and an output voltage of the pixel application voltage detector to apply the common voltage to the common contact point. In claim 1, The pixel applied voltage detector, And three output voltages which detect voltages applied to the pixels of the common electrode contact points formed on the LCD panel among the pixels of the LCD panel and accumulate them to obtain a square root mean square. In claim 2, The pixel for which the pixel applied voltage is detected by the pixel applied voltage detector is And a common voltage generating device adjacent to a common electrode contact point formed on the LCD panel. In claim 2, The addition unit, And three non-inverting amplifiers which use one of the three outputs of the pixel application voltage detector and the output of the common voltage generator as a non-inverting input. In claim 1, The pixel applied voltage detector, And detecting a voltage applied to one of the pixels of the LCD panel. In claim 4, The pixel for which the pixel applied voltage is detected by the pixel applied voltage detector is And a pixel located near the center of the LDC panel. In claim 5, The addition unit, And a non-inverting amplifier comprising the output of the pixel application voltage detector and the output of the common voltage generator as a non-inverting input.