JPS6270818A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To automatically set up common electric potential by providing a common voltage setting circuit with a function for detecting an optimum common potential level and a function for impressing the optimum common potential to a common electrode. CONSTITUTION:A control signal is inputted to a control signal terminal 10 to turn analog switches 5, 8 to ON and OFF states respectively. Since the input impedance of a buffer amplifier 4 is high, the potential of the common electrode 1 becomes a ripple waveform shown in the common potential 17 due to the influence of a video signal impressed to a picture element and the output waveform of an integrating circuit 6 becomes a waveform approximate to the voltage 16 of the DC component of the common potential 17. When the control signal to the control signal terminal 10 is inverted, the voltage of a capacitor 61 is impressed to the common electrode through the analog switch 8. Repeat of said operation at a fixed period makes it possible to make the potential of the common electrode 1 coincide with that of the DC component of the video signal 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device in which the potential of a common electrode of an active matrix liquid crystal panel can be automatically set.

[Summary of the invention]

This invention optimizes the potential of the common electrode by utilizing the fact that the potential of the common electrode in a high impedance state causes ripples due to video signals when setting the potential of the common electrode of an active matrix liquid crystal panel. This allows the value to be automatically set.

[Conventional technology]

2. Description of the Related Art Liquid crystal display devices are attracting attention because they have many advantages such as being thin, light in weight, and low in power consumption. Among these, liquid crystal display devices in which pixels are arranged in a matrix using MIS transistors, which are active switching devices capable of displaying moving images on large-screen high-definition panels and televisions, are attracting particular attention.

In order to prevent deterioration of the liquid crystal, this MA) IJX liquid crystal display device applies an alternating current video signal to the liquid crystal whose polarity is reversed for each screen, with a common electrode as the center potential.

However, the video signals of the two pixel electrodes deviate from the set value due to effects such as the ON resistance of the MIS transistor of one pixel and the parasitic capacitance between the gate and source.

Therefore, it is necessary to set an appropriate common potential for each of the two liquid crystal display devices.

FIG. 2 is a circuit diagram of a common potential setting circuit of a conventional liquid crystal display device. Reference numeral 1 indicates a common electrode provided on the first substrate; 2B indicates a second substrate in which display pixels using MrS transistors or the like are disposed opposite to the first substrate in a matrix; and 3 indicates a common electrode provided on the first substrate; , liquid crystal, 11 is a common voltage setting circuit,
12 is a common potential confirmation terminal, and 13 is a switch.

To set the potential of the common electrode 1, turn off the switch 13, connect a synchroscope to the common potential confirmation terminal 12, measure the DC voltage component of the potential ripple caused by the video signal, and then turn on the switch 13. The output of the common voltage setting circuit 11.

This is done by adjusting the potential to be equal to the potential of the measured DC voltage component.

[Problem that the invention seeks to solve]

Therefore, conventional liquid crystal display devices require a process of inspecting an appropriate common potential and adjusting the common voltage setting circuit to the common potential at the time of shipment.

This led to an increase in manufacturing costs.

Furthermore, if the ON resistance of one pixel MIS transistor changes over time, readjustment is required.

[Means for solving problems]

In order to solve the above problems, the present invention provides a common voltage setting circuit with a function of detecting the optimum common potential and a function of applying the optimum common potential to the common electrode, thereby automatically setting the common voltage. is set.

〔Example〕

1. Configuration of common potential setting circuit (FIG. 1) Embodiments of the present invention will be explained below based on the drawings. In FIG. 1, the common electrodes provided on the first substrate and the display pixels are mapped. The second substrate 2 and liquid crystal 3 provided in an IJ box shape are the same as those in the conventional embodiment shown in FIG. be.

The common potential setting circuit includes common electrodes 1. Voltage amplification factor 1 with high impedance input and low impedance output
the first buffer amplifier of 4. First analog switch5. The common potential detection section connected in this order to the integrating circuit 6 and the integrating circuit 6. A second buffer amplifier 7° with a voltage amplification factor of 1 whose input is high impedance and output is low impedance; second analog switch 8. It is composed of a common voltage application section connected in the order of the common electrode 1.

2. Operating principle of common potential setting circuit (Fig. 1).

Figure 3) Next, use Figures 1, 3 (a), (b), and (C).

The operating principle of the common potential setting circuit will be explained.

Figures 3 (a), Cb) and (c) are time charts [iJ] where the vertical axis V is voltage and the horizontal axis t is time.
a) is a diagram when the video signal 14 applied to the pixels of the second substrate 2 and the common electrode 1 are set to the optimal common potential 15. The video signal 14 is transmitted every time t to display one screen.

The voltage is reversed with respect to the common potential 15.

Therefore, the potential of the DC component of the video signal 14 matches the common potential 15 unless one image changes significantly. Therefore, the DC voltage component applied to the liquid crystal 3 is 0.
It's a bolt.

In FIG. 3(b), the first analog switch 5 is turned on via the inverter 9 by inputting a control signal to the control signal terminal 10.

It is a diagram when the second analog switch 8 is in the OFF state. Since the input impedance of the first buffer amplifier 4 is high, only one common electrode is required.

It is electrically floating. Therefore, the potential of the common electrode 1 has a ripple waveform as shown in the common potential 17 due to the influence of the video signal 14 applied to the two pixels since it is capacitively coupled to the pixels of the second substrate 2. 16 is the potential of the DC component of the common potential 17. The common potential 17 is applied to the input of the integrating circuit 6 through the first buffer amplifier 4 with a voltage amplification factor of 1 and the first analog switch 5.

The time constant of the integrating circuit 6 is such that the video signal engineer 4 has a common potential of 1.
This is set longer than the time t1 for reversing the time t1 for 5.

FIG. 3(C) shows the output waveform of the integrating circuit 6.

Since the ripple component of the common voltage 17 is removed by the integrating circuit 6, the common voltage 18 has a waveform similar to the DC component voltage 16 of the common potential 17.

Next, by inverting the control signal at the control signal terminal 10, the first analog switch 7 is turned off via the inverter 9, while the second analog switch 8 is turned on. . The charge accumulated in the capacitor 61 of the integrating circuit 6 is maintained for a long period of time because the input impedance of the second amplifier 7 is high. This capacity 61
The voltage of the second buffer amplifier 7 with a voltage amplification factor of 1,!
: Applied to the common electrode through the second analog switch 8.

By repeating the above operations at regular intervals.

The potential of the common electrode 1 can be automatically matched to the potential of the DC component of the video signal 14.

〔Effect of the invention〕

As explained above, this invention connects a common potential setting circuit consisting of a buffer amplifier, an analog switch, and an integrating circuit to the common electrode of a matrix liquid crystal panel, thereby achieving a potential at which the DC voltage component of a video signal disappears. The potential of the common electrode is automatically set. Therefore, the manufacturing cost can be reduced by eliminating the step of setting the common potential at the time of shipping the liquid crystal display device. Furthermore, since it can automatically respond to potential fluctuations of the common electrode due to changes over time in the ON resistance of the MIS (MIS) transistor that switches two pixels, it has the effect of extending the life of the liquid crystal and ensuring a beautiful screen display at all times.

[Brief explanation of drawings]

Claims (1)

[Claims] A matrix liquid crystal panel in which a common electrode is formed on one side of a first substrate, and active switching elements such as MIS transistors are mounted on a second substrate facing the first substrate with a liquid crystal interposed therebetween. , a common potential detection section in which a first buffer amplifier, a first analog switch, and an integrating circuit are sequentially connected, and a common potential detecting section is sequentially connected to the integrating circuit, a second buffer amplifier, a second analog switch, and the common electrode. A liquid crystal display device, characterized in that a common voltage setting circuit consisting of a common voltage applying section is connected thereto.