JPH06110035A - Driving method for liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a fine image with high resolution by the active matrix display device by lowering the level of a flicker which causes the display quality to decrease while the irregularity of the flicker on a screen due to an increase in the capacity of gate lines for high density is a technical problem. CONSTITUTION:The rising waveform of a scanning line waveform is, for example, a ramp waveform, exponential function waveform, or staircase waveform. Thus, high frequency components are made small to reduce the potential drop of a pixel potential waveform outputted by a high-pass filter consisting of a transistor, a parasitic capacitance between scanning lines, and a resistance used by regarding the transistor as a variable resistance. Consequently, the flicker can be suppressed low and the image of high quality is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art A signal on a scanning line in a conventional active matrix liquid crystal display has a rectangular wave shown in FIG. By inputting a scanning signal which is sequentially delayed by a pulse width to the scanning line, the gate of the transistor of each pixel in the scanning line is turned on, and the video signal is written to each pixel from the signal line. In the case of the NTSC system TV signal, a scanning signal is applied to each gate line with a pulse width of 63.5 μsec for the horizontal scanning period, and the gate of the transistor connected to the scanning line is kept on during the period.

[0003]

Since the falling waveform of the conventional scanning line signal is also a rectangular wave, the signal has a high high-frequency component. On the other hand, in the pixel equivalent circuit shown in FIG. 4, the exit of the high-pass filter circuit formed by the parasitic capacitance 6 formed by the drain and gate of the transistor 3 and the resistance when the transistor 3 is regarded as a variable resistance is the pixel potential. That is, since the signal of the scanning line has a high frequency component, the signal of the scanning line is not attenuated and communicates with the pixel potential through the parasitic capacitance 6. Therefore, a large potential drop ΔV (ΔV in FIG. 5) occurs, which causes flicker. Further, although it is possible to increase the density by using the active matrix substrate, due to the potential drop of the pixel potential, there occurs a phenomenon that the level of flicker is different in the plane because the capacitance of the gate line is large especially in the high density specifications.

This causes a phenomenon in which even if the common electrode potential is adjusted to a position where flicker is minimized at a certain position in the screen, flicker occurs at another position, so that an appropriate common electrode potential does not exist. This has been a major issue in high-density technology.

[0005]

Data lines and scan lines are arranged in a matrix, and at least one line is provided near the intersection.
An active matrix substrate having one or more switching transistors, a gate of the transistor connected to a scan line, a source of the transistor connected to a data line, and a drain of the transistor connected to a transparent pixel electrode In the liquid crystal display device, the falling waveform of the scanning signal in the driving method of the scanning signal is a ramp waveform, an exponential function waveform, or a stepped waveform.

[0006]

The liquid crystal display having an active matrix substrate among the liquid crystal displays can increase the number of pixels and arrange pixels in the same screen size with high density. This makes it possible to realize a fine, high-resolution, clear screen. As a problem of such a high-density technique, the capacitance attributed to the gate line increases, and a phenomenon occurs in which an appropriate common electrode potential is different in the screen, especially on the left and right of the screen. This means that the flicker distribution occurs due to the variation of the DC component in the plane. These images are very flickering and very difficult to see.

One possible cause of this flicker is that the potential drop due to the gate line in the pixel holding state is different between the left and right sides of the screen. FIG. 4 is an equivalent diagram of one pixel on the active matrix substrate, but the potential drop ΔV in the pixel potential waveform shown in FIG. 5 occurs due to the parasitic capacitance 6 between the drain portion and the gate line of the transistor.

In order to prevent the above-mentioned in-plane distribution of flicker, it is conceivable to reduce the effect of this potential drop ΔV. The potential drop ΔV is a value determined by the voltage of the gate line, that is, the scanning signal, the voltage, and the ratio of the pixel capacitance and the parasitic capacitance in FIG. Pixel capacitance and parasitic capacitance are determined by the specifications and structure of the active matrix substrate, so significant effects cannot be expected. Then, the value of the potential drop ΔV is reduced by the voltage of the scanning signal. However, holding down the high level voltage of the voltage of the scanning signal lowers the writing ability to the pixel, which naturally causes a limitation. If the transistor 3 in FIG. 4 is considered as a kind of variable resistor, the pixel potential is considered to be the scanning signal of the gate line 1 and the exit of the high pass filter via the parasitic capacitance 6 and the transistor (variable resistor) 3. In other words, it is a circuit that allows high-frequency components of the scanning signal to pass without voltage drop.

In order to reduce the potential drop ΔV due to the parasitic capacitance 6, a method of eliminating the high frequency component of the falling waveform of the scanning signal can be considered. Specifically, the falling waveform is formed into a ramp shape or an exponential function waveform so as to have a gentle falling. In addition, the same effect can be expected by forming the falling waveform into a stepwise waveform. With the waveforms of these shapes, the potential drop ΔV due to the scanning signal can be suppressed smaller than usual due to the effect of the high-pass filter circuit. By suppressing the flicker level, it is possible to reduce the in-plane distribution to a negligible extent.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Scanning signal potential waveforms according to the present invention are shown in FIGS. FIG. 2 shows a falling waveform of an exponential function, which can be realized by adding a resistor 8 and a capacitor 7 to the scanning line input section as shown in FIG. When the liquid crystal display device uses an external driver integrated circuit, it can be realized by inserting the above-mentioned resistor and capacitor in the final stage of the driver IC, or by inserting the resistor and capacitor in the scanning line input section on the active matrix substrate. It is possible. The values of these resistances and capacitances are optimized so that they fall with a time constant within the horizontal blanking interval. However, since the rising time also rises with the same time constant, the pixel capacity and the ability to write to the data line sufficiently fast are necessary. By making the falling waveform of the scanning line into an exponential function waveform within a range where there is no influence of the rising time constant, it is possible to eliminate the high frequency component of the scanning line waveform and mitigate the potential drop of the pixel potential waveform.

As another method for realizing the exponential function waveform, there is a method of inserting an inverter as a buffer to optimize the transistor size as shown in FIG. The same effect can be obtained by optimizing the size and current characteristics of the inverter of the final stage buffer circuit in the active matrix substrate in which the driver circuit is incorporated.

Further, as the material of the above-mentioned resistor, in the polysilicon TFT, doped polysilicon of the gate electrode material is considered, and in the amorphous silicon TFT, N ⁺ amorphous silicon or the like may be used.

FIG. 1 shows a ramp waveform in the falling waveform of the scanning signal of the present invention, which can be realized by inserting the circuit using the operational amplifier shown in FIG. 9 before inputting the scanning line. Transistor 3 regarded as a variable resistance in the high-pass filter of FIG. 4 by making a ramp wave
The amount of electric charge that escapes through becomes larger than that of the rectangular wave, and the amplitude becomes smaller. That is, the amount of potential drop in the pixel is reduced, and flicker is suppressed.

Further, it is necessary that the fall time of the ramp wave is within the horizontal blanking interval, which is within 10.9 μs for an NTSC video signal.

Further, FIG. 3 shows a stepwise waveform in the falling waveform of the scanning signal of the present invention. The block diagram shown in FIG. 10 is the circuit of this embodiment. An analog switch 12 is provided after the above-described falling ramp waveform generation circuit, and a staircase wave generation timing pulse is input as its gate pulse. FIG. 11 shows those waveforms. Reference numeral 13 is a gate falling ramp wave voltage waveform, and 14 is a voltage waveform of a staircase generation timing pulse. The waveform of the scanning signal output from the analog switch 12 at this time is shown in FIG. 15 is a staircase waveform of the present invention, which is a timing pulse 14
It is possible to approximate the waveform shown in FIG. 3 by optimizing the duty ratio of. As another method, there is a method of creating a staircase wave using the sample hold circuit shown in the block circuit diagram of FIG. When the sampling switch S is closed, the capacitor C is charged with a voltage equal to the amplitude value of the output ramp waveform from the ramp waveform circuit, and when the sampling switch S is opened next, the capacitor charging voltage is held and output. It is possible to optimize the timing of the sampling time of the sampling switch S and generate a predetermined staircase wave.

[0016]

According to the driving method of the liquid crystal display device of the present invention, the scanning signal is made into the ramp wave shown in FIG. 1, the exponential function wave shown in FIG. 2, or the falling waveform of the staircase wave shown in FIG. The high frequency component of the scanning signal can be reduced. Since the exit of the high-pass filter shown in FIG. 4 is the pixel potential, the pixel potential drop due to the scanning line waveform can be reduced, and the flicker can be suppressed low. Further, in the active liquid crystal display device, it is possible to avoid unevenness in the flicker screen due to high pixel density, and it is possible to realize a fine high-resolution image.

[Brief description of drawings]

FIG. 1 is a falling waveform diagram of a scanning signal ramp wave according to the present invention.

FIG. 2 is a falling waveform diagram of a scanning signal exponential wave according to the present invention.

FIG. 3 is a waveform diagram of a falling edge of a scanning signal staircase according to the present invention.

FIG. 4 is a one-pixel equivalent circuit diagram of the present invention.

FIG. 5 is a pixel potential waveform diagram of a conventional technique.

FIG. 6 is a scanning signal potential waveform diagram of a conventional technique.

FIG. 7 is a block diagram of a scanning signal exponential wave falling wave generation circuit of the present invention.

FIG. 8 is a block diagram of a scanning signal exponential wave falling wave generation circuit of the present invention.

FIG. 9 is a block diagram of a scanning signal ramp wave falling waveform generation circuit according to the present invention.

FIG. 10 is a block diagram of a scanning signal staircase falling waveform generation circuit according to the present invention.

FIG. 11 is a voltage waveform diagram of the scanning signal staircase falling waveform generation circuit block of the present invention.

FIG. 12 is a waveform diagram of a falling edge of a scanning signal staircase according to the present invention.

FIG. 13 is a block diagram of a scanning signal staircase generation circuit of the present invention.

[Explanation of symbols]

 1 Scan Line 2 Data Line 3 Transistor 4 Pixel Capacitance 5 Common Electrode Potential 6 Parasitic Capacitance Between Transistor and Scan Line 7 Exponential Function Falling Wave Generation Capacitance 8 Exponential Function Falling Wave Generation Resistance 9 Exponential Function Falling Wave Generation Inverter 10 Operational Amplifier 11 Inverter 12 Analog Switch 13 Ramp Falling Waveform 14 Staircase Wave Generation Timing Pulse 15 Stepwise Falling Scan Signal Waveform 16 Operational Amplifier in Sample Hold Circuit 17 Sampling Switch

Claims (3)

[Claims] 1. A data line and a scan line are arranged in a matrix, and at least one switching transistor is provided near an intersection of the data line and the scan line, the gate of the transistor is connected to the scan line, and the source of the transistor is In a liquid crystal display device having an active matrix substrate connected to a data line and having a drain of the transistor connected to a transparent pixel electrode, a falling waveform of a pulse in a voltage waveform of a scanning signal is a ramp waveform. And a method for driving a liquid crystal display device. 2. The method of driving a liquid crystal display device according to claim 1, wherein the falling waveform of the pulse in the voltage waveform of the scanning signal is an exponential function waveform. 3. A method of driving a liquid crystal display device according to claim 1, wherein the falling waveform of the pulse in the voltage waveform of the scanning signal is a stepwise waveform.