JP2000221474A - Method for driving liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the uniformity of display screen from being impaired due to that charges stored in a pixel electrode are charged/discharged by on/off of a gate pulse signal and the voltage held by the pixel electrode is fluctuated when a liquid crystal display device is driven. SOLUTION: A buffer circuit 15 making possible the control of a source voltage for the gate pulse signal generated by a vertical scan driver circuit 12 from the outside is provided, and the source voltage applied to the buffer circuit 15 in an on period while a video signal is written in the pixel electrode is controlled in a sinewave shape by a source 16 for a buffer. Thus, the source voltage is controlled so as to change smoothly the rise and fall shape of the gate pulse signal waveform applied to a gate electrode of a switching transistor, and the voltage fluctuation of the pixel electrode is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of driving an active matrix type liquid crystal display device (international patent classification G02).
F 1/13).

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for large-screen image display devices for enjoying powerful images with the enhancement of video equipment such as video tape recorders and video disk players and video software. As a conventional large-screen image display device, there has been a television using a CRT.
Since the CRT is used for the image display unit, there is a limitation in miniaturizing the apparatus due to physical restrictions of the CRT. A liquid crystal display device using a liquid crystal panel for an image display unit has been proposed in order to eliminate this limitation and reduce the size of the device.

An example of a conventional liquid crystal display device using a liquid crystal panel is disclosed in, for example, Japanese Patent Application Laid-Open No. 4-188104.

FIG. 4 is a diagram showing a configuration of an example of a conventional liquid crystal display device using a liquid crystal panel.

In FIG. 4, an input video signal is processed by a video signal processing circuit 61 into a form for displaying an image on a liquid crystal panel 51 and applied to a horizontal scanning driver circuit 54. Further, the horizontal synchronizing signal and the vertical synchronizing signal are separated from the video signal by the synchronizing signal separating circuit 62, and are applied to the liquid crystal panel drive control circuit 63. The liquid crystal panel drive control circuit 63 generates a control signal for displaying an image on the liquid crystal panel 51 from the input synchronization signal, and outputs the control signal to the horizontal scanning driver circuit 5.
4 and the vertical scanning driver circuit 55.

[0006] In order to display an image on the liquid crystal panel 51, a horizontal scanning driver circuit 54 performs horizontal scanning, and a vertical scanning driver circuit 55 performs vertical scanning. Here, the scanning in the vertical direction is performed for all the lines on the liquid crystal panel 51 in order. The video signal lines 5 are displayed at the timing of displaying an image from each driver circuit.
6 is applied to the scanning signal line 57 and the transistor 5
An image is displayed on the liquid crystal panel 51 by controlling 3 and applying a signal to the display pixel 52.

FIG. 5 is an equivalent circuit for explaining one pixel portion of the liquid crystal panel 51.

[0008] A switching transistor Tr is provided at the intersection of the scanning signal line Xi and the video signal line Yi.
The gate electrode G of the transistor Tr is connected to the scanning signal line Xi, and a gate pulse signal Vg for driving the transistor Tr is applied. The source electrode S is connected to the video signal line Yi, and the video signal Vsig is supplied. The liquid crystal pixel is equivalently represented by a liquid crystal capacitance _CLC , and is connected to the drain electrode D of the transistor Tr. Generally the auxiliary capacitor Cs is connected in parallel to the liquid crystal capacitance C _LC. The potential Vcom of the counter electrode is applied to one terminal of the liquid crystal capacitance _CLC and one terminal of the trapping capacitance Cs. Between the gate electrode G and the liquid crystal capacitance C _LC is a parasitic capacitance Cgd exists consisting of a parasitic capacitance component between the gate region and the source region of the transistor Tr.

FIG. 6 is a timing chart showing an example of a conventional driving method of a liquid crystal display device.

As described above, the vertical scanning of the liquid crystal panel 51 is performed by outputting the gate pulse signals from the vertical scanning driver circuit 55 for all the lines one by one in order. A certain scanning signal line X
The gate pulse signal output from the vertical scanning driver circuit 55 for i is a voltage Vg-on for turning on the transistor Tr during the on period, and a voltage Vg-off for turning off the transistor Tr during the off period. Has been applied. Thereby, the video signal line Y is turned on during the ON period.
i is supplied to the transistor T
The data is written to the liquid crystal capacitance _CLC and the auxiliary capacitance Cs by r. On the other hand, since the transistor Tr is in the off state during the off period, the charge written in the liquid crystal capacitance _CLC and the auxiliary capacitance Cs is held as it is.

[0011]

As described above, in a liquid crystal display device, an image is displayed by writing / holding a video signal in a liquid crystal pixel by turning on / off a gate pulse signal. When the voltage falls from the on-state voltage Vg-on to the off-state voltage Vg-off, or on the contrary, when it rises, the charges accumulated in the liquid crystal pixels are charged and discharged by the above-described parasitic capacitance Cgd. When the gate pulse signal rises, a new video signal Vsig is immediately written, so there is no problem. However, when the gate pulse signal falls, a voltage fluctuation ΔV occurs in the video signal Vsig written during the ON period. This ΔV is represented by ΔV =
It is represented by Cgd / (C _LC + Cgd + Cs) × Vgd.

The value of the parasitic capacitance Cgd varies from pixel to pixel, and the waveform of the gate pulse signal applied to the gate electrode G of the transistor Tr differs between the beginning and end of the scanning signal line due to the impedance of the scanning signal line. Therefore, there is a problem in that the voltage fluctuation ΔV varies, thereby deteriorating the uniformity on the display screen and deteriorating the display image quality.

[0013]

In order to solve the above-mentioned problems, a method of driving a liquid crystal display device according to the present invention comprises an active matrix in which pixel electrodes having at least one or more switching transistors are arranged in a matrix. A method for driving a liquid crystal display device comprising a liquid crystal layer sandwiched between a substrate and a common electrode substrate having a transparent electrode, wherein a video signal is applied to a gate electrode of the switching transistor during a selection period during writing to the pixel electrode. It is characterized in that the waveform of the gate pulse signal to be applied is controlled to be smoothly changed.

According to the present invention, the variation in the electric charge held in the liquid crystal pixels caused by the driving of the liquid crystal display device is reduced, so that the uniformity on the display screen is maintained and the liquid crystal display device has good display quality. Can be provided.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A driving method of a liquid crystal display device according to the present invention is directed to a method of driving a liquid crystal display using a common electrode substrate having transparent electrodes and an active matrix substrate having pixel electrodes having at least one switching transistor arranged in a matrix. What is claimed is: 1. A method for driving a liquid crystal display device having a layer sandwiched therebetween, comprising: a vertical scanning circuit for performing vertical scanning of the liquid crystal display device; and a switching transistor for the pixel electrode generated by the vertical scanning circuit. A buffer circuit capable of externally controlling a power supply voltage with respect to a gate pulse signal applied to the gate electrode, and a power supply voltage applied to the buffer circuit during an ON period while a video signal is written to the pixel electrode. Is controlled in a sine-wave form, whereby the gate electrode applied to the gate electrode of the switching transistor is controlled. It is obtained by said controlling so smoothly changing the rise and fall shapes of the scan waveform, by reducing the variation of the electric charge held in the liquid crystal pixel caused by the driving of the liquid crystal display device,
This has the effect of maintaining uniformity on the display screen and obtaining good display image quality.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG.

(Embodiment) FIG. 1 is a configuration diagram showing a configuration of a liquid crystal display device according to a driving method of a liquid crystal display device according to an embodiment of the present invention. A liquid crystal pixel portion for display; 3 a transistor for controlling image display on the liquid crystal pixel portion 2; 4 a storage capacitor provided in parallel with the liquid crystal display portion;
Reference numeral 5 denotes a parasitic capacitance caused by a parasitic capacitance between the gate electrode and the drain electrode of the transistor 3, reference numeral 11 denotes a horizontal scanning driver circuit for performing horizontal scanning for displaying an image on the liquid crystal panel 1, and reference numeral 12 denotes a vertical scanning similarly. A vertical scanning driver circuit 13 for transmitting a video signal from the horizontal scanning driver circuit 11; a scanning signal line 14 for transmitting a scanning signal from the vertical scanning driver circuit 12; A buffer circuit for supplying a gate pulse signal generated by the vertical scanning driver circuit 12 to the scanning signal line 14, and a buffer power supply 16 for supplying a voltage to the buffer circuit 15 from outside the liquid crystal panel 1.

The buffer power supply 16 changes the output voltage in a sinusoidal manner and supplies it to the buffer circuit 14 during the ON period of the scanning signal line.

FIG. 2 is a schematic diagram for explaining the output voltage of the buffer power supply 16 and the state of the gate pulse signal output to the scanning signal line by the buffer circuit 15.

FIG. 2A shows the output voltage of the buffer power supply 16. The output voltage of the buffer power supply 16 is a sinusoidal varying amplitude V ₁ for a constant voltage V _0, the output voltage when switching the scanning signal lines to be turned on is controlled to be the minimum .

FIGS. 2B and 2C show the state of gate pulse signals output to certain scanning signal lines Xi and Xi + 1. The gate pulse signal during the ON period is
It changes in a sinusoidal manner according to the change in the output voltage of the buffer power supply 16.

The operation of the liquid crystal display device using the driving method of the liquid crystal display device configured as described above will be described with reference to FIG.

FIG. 3 is a timing chart for explaining the operation of one pixel.

As described in the description of the prior art, when the gate pulse signal falls from the ON state to the OFF state, the charge accumulated in the pixel electrode is discharged by the parasitic capacitance Cgd and written during the ON period. The voltage fluctuation ΔV is caused to the video signal Vsig. The gate pulse signal supplied to the scanning signal line is controlled in a sine wave shape by controlling the output voltage of the buffer power supply 16 as described above. Therefore, the amount of voltage change when the gate pulse signal falls from the on-state voltage Vg-on to the off-state voltage Vg-off is small.

When the gate pulse signal is controlled in this manner, Vgd becomes smaller in a voltage fluctuation represented by ΔV = Cgd / (C _LC + Cgd + Cs) × Vgd.
V can be reduced.

As described above, by controlling the power supply voltage to be supplied to the buffer circuit of the scanning signal line in a sinusoidal manner and controlling the gate pulse signal to change smoothly, the voltage fluctuation of the liquid crystal pixel due to the parasitic capacitance Cgd is controlled. , The uniformity on the display screen can be maintained, and a great effect of obtaining good display image quality can be obtained.

[0027]

As described above, according to the method of driving a liquid crystal display device of the present invention, an active matrix substrate in which pixel electrodes having at least one switching transistor are arranged in a matrix and a transparent electrode are provided. A method for driving a liquid crystal display device having a liquid crystal layer sandwiched between common electrode substrates, comprising: a vertical scanning circuit for performing vertical scanning of the liquid crystal display device; and the pixel generated by the vertical scanning circuit. A buffer circuit capable of externally controlling a power supply voltage with respect to a gate pulse signal applied to a gate electrode of a switching transistor of the electrode, wherein the buffer circuit is turned on during a period during which a video signal is written to the pixel electrode. The power supply voltage applied to the switching transistor is controlled in a sine wave shape, thereby printing on the gate electrode of the switching transistor. The liquid crystal display device can be provided so as to maintain uniformity on the display screen and obtain good display image quality by controlling the rising and falling shapes of the gate pulse signal waveform to be smoothly changed. There is a great effect that it can be done.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a configuration of a liquid crystal display device according to a driving method of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining an output voltage of a buffer power supply and a state of a gate pulse signal according to the driving method.

FIG. 3 is a timing chart for explaining the operation of one liquid crystal pixel by the driving method.

FIG. 4 is a configuration diagram of an example of a conventional liquid crystal display device.

FIG. 5 is a diagram showing an equivalent circuit for explaining one pixel portion of a liquid crystal panel.

FIG. 6 is a timing chart showing an example of a conventional driving method of a liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal panel 2 Liquid crystal pixel part 3 Transistor 4 Auxiliary capacitance 5 Parasitic capacitance 11 Horizontal scanning driver circuit 12 Vertical scanning driver circuit 13 Video signal line 14 Scanning signal line 15 Buffer circuit 16 Buffer power supply

Claims (2)

[Claims] 1. A method of driving a liquid crystal display device comprising a liquid crystal layer sandwiched between an active matrix substrate having pixel electrodes having at least one or more switching transistors arranged in a matrix and a common electrode substrate having transparent electrodes. Wherein a control is performed such that a waveform of a gate pulse signal applied to a gate electrode of the switching transistor is smoothly changed during an ON period during which a video signal is written to the pixel electrode. Drive method. 2. A method for driving a liquid crystal display device comprising a liquid crystal layer sandwiched between an active matrix substrate having pixel electrodes having at least one or more switching transistors arranged in a matrix and a common electrode substrate having transparent electrodes. A vertical scanning circuit for performing vertical scanning of the liquid crystal display device; and a gate pulse signal generated by the vertical scanning circuit and applied to a gate electrode of a switching transistor of the pixel electrode. A switching circuit that controls the power supply voltage applied to the buffer circuit in a sine-wave shape during an ON period during which a video signal is written to the pixel electrode, comprising: Rising and falling shapes of the gate pulse signal waveform applied to the gate electrode Method of driving a liquid crystal display device comprising a control that such smooth changing.