JPH0566386A - Method for driving liquid crystal display device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a driving method of an active matrix type liquid crystal display device using thin film transistors, which has less flicker and afterimage and excellent display quality. [Structure] A different voltage or a voltage having a gradient is applied to a common voltage applied to a common electrode depending on coordinates on a substrate. [Configuration] Since a voltage close to a common voltage that minimizes different flicker is applied to the liquid crystal cells of each coordinate, flicker and afterimage can be significantly reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique effectively applied to a liquid crystal display device, for example, a liquid crystal display device having an active matrix structure in which a liquid crystal is driven by using a TFT (thin film transistor).

[0002]

2. Description of the Related Art As a method of driving a common voltage of a liquid crystal display device having a TFT active matrix structure, for example, there is a flat panel display, item 80-87, published on Nov. 26, 1990, edited by Nikkei BP. In this example, the common voltage Vcom is a constant DC voltage in the substrate.

[0003]

The TFT liquid crystal display device is mainly used as a monitor in a microcomputer as a small and low power consumption display device. As a display quality problem of the active matrix liquid crystal display device for such an application, there are flicker which is a flicker of a screen and an afterimage which occurs when an image is switched. In particular, in a TFT liquid crystal display device having a diagonal of 10 inches or more, the conventional driving method in which the common voltage is constant causes a large flicker, which has been found to be a practical problem.

FIG. 7 shows a constitutional view of a glass substrate on which a TFT is formed in a liquid crystal display device measured by the inventor. In the figure, the liquid crystal display unit 8 is provided with TFTs for a plurality of liquid crystal cells (LC) arranged in a matrix.
Each liquid crystal is driven by the switching operation of the FT. Here, a gate voltage is supplied from a gate drive circuit 1 connected to one side of the substrate to a gate line, which is an electrode commonly drawn from the gates of the TFTs arranged in the horizontal direction. On the other hand, the drain voltage is also supplied from the data driving circuit 2 to the drain line, which is an electrode commonly drawn from the drains of the TFTs arranged in the vertical direction. On the other hand, on the liquid crystal cell, for example, a Twisted Nematic type liquid crystal layer 4 is sealed in a gap with the second counter glass substrate 5. The common glass substrate 5 has a common voltage Vc applied to the liquid crystal layer 4.
A common electrode 6 formed of a transparent electrode for applying om is formed, and the common electrode 6 is supplied with Vcom from a power supply circuit 7 through a connection terminal 10 in order to connect to the outside. The connection terminal 10 is formed in a square on the substrate.

FIG. 8 shows the value of the common voltage Vcom applied to the counter glass substrate which minimizes the flicker in each pixel along the gate line in the liquid crystal display unit 8 of FIG. The liquid crystal display device has a diagonal of 10 inches, and the measurement is in a display mode in which a drain voltage having a transmittance of 50% is applied at each measurement point. From FIG. 8, it was found that the value of Vcom that minimizes the flicker is different in each liquid crystal cell and increases toward the center of the screen from the position where the gate drive circuit is connected. Therefore, when the conventional driving method is used, only a constant Vcom is given by this driving method. Therefore, when Vcom that minimizes the flicker in the center of the screen is given, the gate driving circuit 1
In a liquid crystal cell close to, there is a problem that flicker is large.

An object of the present invention is to provide a driving method of a liquid crystal display device which solves the above-mentioned flicker and afterimage.

[0007]

The object of the present invention is achieved by applying a common voltage Vcom applied to a counter glass substrate to different voltages depending on a position along one side of a gate drive circuit connected to a gate line. To be done.

[0008]

The purpose of the present invention is to provide a voltage close to the common voltage that minimizes flicker on the screen by externally applying the common voltage value so as to vary depending on the position along the gate line. It is possible to provide a liquid crystal display device having good display performance with little flicker and afterimage in the entire screen area.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a schematic assembly diagram of an active matrix type liquid crystal display device using the driving method of the present invention.

In the figure, the liquid crystal display section 8 is provided with TFTs for a plurality of liquid crystal cells (LC) 9 arranged in a matrix, and each liquid crystal is driven by the switching operation of the TFTs. And this is the first T
It is formed on the FT glass substrate 3. Here, a gate voltage is supplied from a gate drive circuit 1 connected to one side of the substrate to a gate line which is an electrode commonly drawn from the gates of the TFTs arranged in the horizontal direction. On the other hand, the drain voltage is also supplied from the data driving circuit 2 to the drain line which is an electrode commonly drawn from the drains of the TFTs arranged in the vertical direction. On the other hand, on the liquid crystal cell, for example, a Twisted Nematic type liquid crystal layer 4 is sealed in a gap with the second counter glass substrate 5. A common electrode 6 formed of a transparent electrode for applying a common voltage Vcom to the liquid crystal layer 4 is formed on the counter glass substrate 5, and the common electrode 6 is connected to the outside by a power supply circuit 7 through a connection terminal 10. Vcom
Is being supplied. In this embodiment, the connection terminal 10 is formed in a square shape of the board. A feature of this embodiment is that, of the four connection terminals, the common voltage Vcom1 of two terminals close to the gate drive circuit 1 is different from the common voltage Vcom2 of the other two terminals. The voltage relationship is Vcom1 <Vcom2.

Next, the operation of the first embodiment will be described with reference to FIG. FIG. 2 is a drive waveform of a common voltage according to an embodiment of the present invention, which is measured along the gate line on a line passing through the center of the liquid crystal display device from the gate drive circuit 1 (on the I-II line in FIG. 1). It is a comparison of the common voltage value that minimizes flicker at each liquid crystal cell position and the value of the common voltage proposed by this embodiment, and the solid line indicates the measured voltage value that minimizes flicker at each liquid crystal cell position. The broken line is the common voltage Vcom supplied by the method of this embodiment. In this embodiment, since the common voltages Vcom1 and Vcom2 are applied from the outside, there is a voltage gradient on the common electrode. Therefore, a voltage close to the voltage that minimizes flicker is applied, and the DC voltage used in the conventional technique is changed. Compared with this, there is an effect that flicker and afterimage of the liquid crystal display device can be reduced.

FIG. 3 shows a second embodiment of an assembly schematic diagram of an active matrix type liquid crystal display device using the driving method of the present invention. In the present invention, in addition to the square of the substrate, the connection terminal 10 has a connection terminal formed at the center of the side orthogonal to the one side to which the gate drive circuit 1 is newly connected. The common voltage Vcom2 is applied to these two new terminals, and the magnitude relationship of the voltages is Vcom1 <Vcom2.

Next, the operation of the second embodiment will be described with reference to FIG. FIG. 4 is a drive waveform of a common voltage according to an embodiment of the present invention, which is measured along the gate line on a line passing through the center of the liquid crystal display device from the gate drive circuit 1 (on the I-II line in FIG. 3). It is a comparison of the common voltage value that minimizes flicker at each liquid crystal cell position and the value of the common voltage proposed by this embodiment, and the solid line indicates the measured voltage value that minimizes flicker at each liquid crystal cell position. The broken line is the common voltage Vcom supplied by the method of this embodiment. This embodiment has a problem that the number of connection terminals is increased as compared with the first embodiment, but since the voltage of Vcom2 is applied to the center of the screen,
There is a voltage gradient between one side of the substrate to which the drive circuit 1 is connected and the center of the screen, and a voltage closer to the voltage that minimizes the flicker than that in the first embodiment is applied, and it is possible to reduce the flicker and the afterimage of the liquid crystal display device. There is an effect to say. FIG. 5 shows a third embodiment of a schematic assembly diagram of an active matrix type liquid crystal display device using the driving method of the present invention. A common electrode 6 formed of a transparent electrode for applying a common voltage Vcom to the liquid crystal layer 4 is formed on the counter glass substrate 5, and the common electrode has two slits formed in the drain line direction.
To each of the separated common electrodes 6, Vcom is supplied from the power supply circuit 7 through the connection terminal 10 in order to connect to the outside. In this embodiment, the connection terminal 10 is connected to each common electrode, three different common voltages are applied, and the magnitude relationship of the voltages is Vcom1 <Vcom2 <Vcom3.

Next, the operation of the third embodiment will be described with reference to FIG. FIG. 6 is a drive waveform of a common voltage according to an embodiment of the present invention, which is measured on a line passing through the center of the liquid crystal display device from the gate drive circuit 1 (on line I-II in FIG. 5) along the gate line. It is a comparison of the common voltage value that minimizes flicker at each liquid crystal cell position and the value of the common voltage proposed by this embodiment, and the solid line indicates the measured voltage value that minimizes flicker at each liquid crystal cell position. The broken line is the common voltage Vcom supplied by the method of this embodiment. This embodiment has a problem that the number of steps for forming the slits is increased as compared with the first and second embodiments. However, since the liquid crystal resistance is high, a current does not flow through the common electrode and power consumption is small. In addition to the above effect, a common voltage on the stairs can be applied along the gate line, so that a voltage close to a voltage that minimizes flicker is applied, and flicker and afterimage of the liquid crystal display device can be reduced. ..

[0016]

According to the present invention, it is possible to easily provide a common voltage that reduces flicker and an afterimage, which are problems in display quality of a liquid crystal display device, so that a liquid crystal display device having excellent display quality can be provided.

[Brief description of drawings]

FIG. 1 is an assembly diagram of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a common voltage waveform according to an embodiment of the present invention.

FIG. 3 is an assembly diagram of a liquid crystal display device according to an embodiment of the present invention.

FIG. 4 is a diagram showing a common voltage waveform according to an embodiment of the present invention.

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

FIG. 6 is a diagram showing a common voltage waveform according to an embodiment of the present invention.

FIG. 7 is an assembly diagram of a conventional liquid crystal display device.

FIG. 8 is a diagram showing a common voltage waveform in a conventional method.

[Explanation of symbols]

Vcom ... Common voltage, 1 ... Gate drive circuit, 2 ... Data drive circuit, 3 ... Data drive circuit, 4 ... Liquid crystal layer, 5 ... TFT glass substrate, 6 ... Common electrode, 7 ... Power supply, 8 ... Liquid crystal display section,
9 ... Liquid crystal cell, 10 ... Connection terminal.

Claims (5)

[Claims] 1. A first glass substrate on which a thin film transistor is formed as a switching element, a second glass substrate to which a common voltage is applied at a position facing the first glass substrate, and a gap between the first and second gaps. In a liquid crystal display device having a drive circuit for enclosing a liquid crystal and supplying a voltage to the gate of the thin film transistor, a common voltage applied to the second substrate has two or more voltages that differ depending on coordinates on the substrate. A method for driving a liquid crystal display device, comprising: 2. A first glass substrate on which a thin film transistor is formed as a switching element, a second glass substrate to which a common voltage is applied at a position facing the first glass substrate, and the first and second gaps. A liquid crystal display device having a drive circuit for enclosing a liquid crystal and supplying a voltage to the gate of the thin film transistor, wherein the common voltage applied to the second substrate has a voltage gradient on the substrate. Driving method. 3. The liquid crystal display device according to claim 1, further comprising a drive circuit for supplying a voltage to a gate of the thin film transistor on one side of a first glass substrate having four sides, wherein the drive circuit is connected to the liquid crystal display device. A method for driving a liquid crystal display device, wherein the common voltage applied to the liquid crystal increases stepwise from one side of the first glass substrate toward the center of the first glass substrate along the gate wiring. .. 4. The liquid crystal display device according to claim 2, further comprising a drive circuit for supplying a voltage to a gate of the thin film transistor on one side of a first glass substrate having four sides, wherein the drive circuit is connected. A method for driving a liquid crystal display device, wherein a common voltage applied to the liquid crystal has a voltage gradient from one side of the first glass substrate toward the center of the first glass substrate along the gate wiring. 5. The liquid crystal display device according to claim 1, further comprising a driving circuit for supplying a voltage to a gate of the thin film transistor on one side of a first glass substrate having four sides, wherein the driving circuit is connected. A method of driving a liquid crystal display device, wherein a common voltage applied to the center of the first glass substrate along the gate wiring from two opposite sides of the first glass substrate is higher than the common voltage of other portions. ..