JPH0651277A - Active matrix liquid crystal display - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display having high quality of display by providing a discharging resistance element somewhere within a switching element driving voltage line. CONSTITUTION:Driving voltages VGG are input from a data line 13, and each scanning line 15 is provided with an analog switch 11, and either of the voltages VGG is selected on the basis of a sampling pulse sent from a shift register 10 and is output to each scanning line. Inside a display module 6, the data line 13 is connected to reference potential, e.g. a GND level via a resitance element 14. A high resistance element of 100kOMEGA to 1MOMEGA is usable as 14. Therefore, even if the power supply is turned off with a specific analog switch 11 being connected to the driving voltage VGG, for example, a charge stored in a VGG line in a control circuit 1 is discharged via the resistance element 14.

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, and more particularly to an active matrix type liquid crystal display device having a switching element for each pixel.

[0002]

2. Description of the Related Art In an active matrix type liquid crystal display device, since a pixel electrode is controlled by a switching element provided for each pixel, high density and high definition image display can be obtained. The conventional active matrix type liquid crystal display device will be described below.

FIG. 4 is an equivalent circuit diagram showing the basic structure of an active matrix liquid crystal display device. That is, the scanning lines 40 and the signal lines 41 are formed in a matrix on the array substrate, and a switching element (hereinafter referred to as a TFT) 4 formed of a thin film transistor is provided at each intersection of the scanning lines 40 and the signal lines 41.
The pixel electrode 43 is connected via 2. TFT42
The gate electrode is connected to the scanning line 40, and the drain electrode is connected to the signal line 41. The source electrode is connected to the pixel electrode 43. On the other hand, the counter electrode 44 is formed on the entire surface of the counter substrate.
A liquid crystal layer 45 is sandwiched between the pixel electrode 43 and the pixel electrode 43.

Next, a method of driving a conventional liquid crystal display device will be described. When a predetermined selection voltage VGG sent from the row driver 46 is applied to the scanning line 49, the TFT 42 becomes conductive and the video signal sent from the column driver 47 is written in the pixel electrode 43. Then, when the non-selection voltage is applied to the scanning line 40, the TFT 42 becomes non-conductive, and the pixel electrode 43 holds the written potential until the next selection voltage is applied. On the other hand, the counter electrode 4
4 is set to a predetermined potential, and the transmittance of the liquid crystal layer 45 changes according to the potential difference between the pixel electrode 43 and the counter electrode 44, and display is performed.

FIG. 5 shows an example of a drive circuit of a conventional liquid crystal display device. Inside the control circuit 51, there is provided a power supply circuit 52 which generates a TFT element drive voltage VGG of the pixel portion and an operating voltage VDD of the circuit based on an external input voltage.
The drive voltage VGG and the operating voltage VDD are respectively filtered by the filter 5
3, the row driver 5 via the smoothing capacitor 54, etc.
Sent to 7.

[0006] VGG is a voltage for switching the TFT of the pixel portion, and is usually 20 to 2 with respect to the reference potential.
It is set to a voltage of 5V. On the other hand, VDD is the operating voltage of the drive circuit element and is normally set to a voltage of about 5V.

[0007]

However, the conventional liquid crystal display device has a problem that a black stripe-shaped display defect occurs when the power is turned on. In particular, when this display defect occurs on a specific display line, the display quality is significantly impaired. An object of the present invention is to eliminate such a display defect and obtain a liquid crystal display device having high display quality.

[0008]

In order to solve such a problem, the present invention provides a liquid crystal panel in which a switching element composed of a transistor is arranged for each pixel, and a switching element drive voltage for the liquid crystal panel. In a liquid crystal display device including a control circuit that supplies a circuit operating voltage and a row driver that controls a switching element, a switching element driving voltage that is input to the row driver when the power supply of the control circuit is turned off quickly rises. A liquid crystal display device that can be lowered is used. Furthermore, a liquid crystal display device in which a discharge resistance element is provided in the switching element drive voltage path input from the control circuit to the row driver is used.

[0009]

The present inventors have found the following as a result of intensive studies on the above-mentioned problems. That is, the drive voltage V
GG is a voltage for driving the TFT element in the pixel section. Therefore, the internal load in the intermediate path for inputting this VGG to the row driver basically stays in the rectifying element such as the filter and the smoothing capacitor as illustrated. Therefore, the power consumption in the VGG route is several tens of μA.
The voltage stored in the smoothing capacitor, for example, is extremely small, and it takes about several tens of minutes to discharge the voltage very slowly. When such a voltage is applied to the TFT in the pixel portion in a direct current manner, the current-voltage characteristic of the TFT varies. The reason for this is not clear, but it is considered that the cause is that the charging phenomenon occurs due to the application of the DC voltage to the TFT element or the array substrate for a long time. When the characteristics of the TFT change in this way, an unnecessary video signal is applied to the pixel electrode, which causes display defects such as black streaks.

In the liquid crystal display device of the present invention, the power source O
During FF, it is possible to discharge the electric charge accumulated inside the circuit and prevent the DC voltage from being applied to the TFT element in the pixel portion for a long time.

[0011]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below. FIG. 1 shows a drive circuit of a liquid crystal display device in this embodiment.

The display module 6 is a drive circuit for the liquid crystal panel, and is composed of a row driver for driving the TFTs of the pixel portion, a column driver for controlling the video signal, and the like.

The power supply circuit 2 is a circuit for generating a TFT element drive voltage VGG of the pixel portion and an operation voltage VDD of the drive circuit based on an external input voltage, and is composed of, for example, a DC-DC converter. The drive voltage VGG is input to the row driver inside the display module 6 via the VGG line 8.

FIG. 2 shows an example of a specific configuration of the row driver.
Shown in. That is, the drive voltage VGG is supplied from the data line 13.
Is entered. Each scan line 15 has an analog switch 1
1 is provided, and VGG is selected based on the sampling pulse sent from the shift register 10 and output to the scanning line.

In this embodiment, the display module 6
Internally, the data line 13 is connected to a reference potential, for example, the GND level via the resistance element 14. As the resistance element 14, a high resistance element of 100 KΩ to 1 MΩ can be used. By using such a resistance element, the TFT element performs a normal operation during operation and can solve the conventional problems that occur when the power is turned off.

That is, for example, a specific analog switch 11
Even when the power source is turned off in the state of being connected to the VGG side, the electric charge accumulated in the VGG path inside the control circuit 1 is discharged through the resistance element 14. Therefore, it is possible to prevent the DC voltage from being applied to the specific scanning line for a long time. Therefore, it is possible to suppress the fluctuation of the current-voltage characteristics of the TFT element and suppress the occurrence of display defects such as black streaks when the power is turned on.

In the above-described embodiment, the data line 13 is connected to the reference potential via the resistance element 14 in order to discharge the charge accumulated in the intermediate path for inputting VGG to the row driver. It is not limited to the method. Another embodiment of the present invention will be described below. (Example 2)

FIG. 3 shows a circuit diagram of the display module in this embodiment. That is, VGG input from the control circuit is supplied to the row driver 20 via the transistor Q1.
It is input to the side and is connected to the reference potential via the resistance element R1.

On the other hand, VDD input from the control circuit is the operating voltage of the drive circuit element. Since the power consumption inside the circuit is large on the VDD line side, the potential falls sharply when the power is off compared to the VGG line 8 side. At this time, the potential supplied from the transistor Q2 connected to the VDD line 9 to the transistor Q1 becomes VGG potential, and the transistor Q1 is turned off, whereby the row driver 20 and the VGG line are electrically disconnected. Becomes

That is, in this embodiment, the row driver 20 is driven to V by the fall of the operating voltage VDD of the drive circuit.
Since it is cut off from the GG line 8, it is possible to prevent a DC potential from being applied to the TFT element in the pixel portion for a long time.

Further, by using such a structure, the following effects can be obtained. That is, when the power is turned on, the input of the operating voltage VDD of the drive circuit to the row driver is VGG
If the delay is delayed, the row driver will momentarily malfunction and the VGG potential will be supplied to the specific line.
There is a possibility that the characteristics of the TFT may deteriorate.

In this embodiment, since VDD is applied when the power is turned on and the row driver 20 is connected to the VGG line, the input of VDD is not delayed from VGG. Therefore, the problem that the VGG potential is supplied to the specific scan line due to the malfunction of the row driver IC can be solved.

[0023]

As described above in detail, in the liquid crystal display device of the present invention, it is possible to prevent the DC potential from being applied to the row driver for a long time due to the electric charge accumulated in the circuit when the power is turned off. be able to. Therefore, it is possible to prevent the current-voltage of the TFT element in the pixel portion from fluctuating, and suppress the occurrence of display defects such as black streaks.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a drive circuit of a liquid crystal display device of the present invention.

FIG. 2 is a circuit diagram showing a part of a drive circuit according to an embodiment of the present invention.

FIG. 3 is a circuit diagram showing a part of a drive circuit according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a basic structure of one pixel of a liquid crystal display device.

FIG. 5 is a circuit diagram showing a conventional liquid crystal display device.

[Explanation of symbols]

 1 ... Control circuit 2 ... Power supply circuit 5 ... Internal load 6 ... Display module 14 ... Resistor element

Claims (1)

[Claims] 1. A liquid crystal panel in which a switching element composed of a transistor is arranged for each pixel, a control circuit for supplying a switching element drive voltage and a circuit operating voltage to the liquid crystal panel, and a switching element for controlling the switching element. A liquid crystal display device including a row driver, wherein a switching element drive voltage input to the row driver is quickly lowered when the control circuit is powered off.