JPS58122596A - Image display unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal supply circuit for a liquid crystal display device in which active switching elements are arranged in a matrix.

A liquid crystal display device in which QM switch elements are arranged in a matrix can display an image by sequentially turning on the active switch elements in synchronization with a television synchronization signal and sequentially applying a video signal to each pixel. ◇ In late crystal displays, liquid crystal is sealed between facing electrodes that have been subjected to orientation treatment, and display is performed by applying voltage to the facing electric field. In a so-called active panel in which active elements are usually arranged in an IJ box shape, there is a matrix of active elements on the lower side and pixel electrodes that are switched by the active elements.

A transparent common electrode is formed inside the upper glass plate. Furthermore, since liquid crystals deteriorate when DC voltage is applied, they are usually driven with AC voltage.

Therefore, the common electrode is usually fixed at one foot of DC level,
Although it is necessary to reversely drive the counter electrode in positive and negative directions with respect to the common electrode, it is quite difficult to prevent a DC voltage component from being applied to the liquid crystal, as will be described later. However, an object of the present invention is to automatically adjust the voltage of the common electrode according to the drive signal so that the DC voltage component is not applied to the liquid crystal when driving the active panel. Detailed explanation.

Figure 1 shows an example of a television receiver using a conventional drive system using a liquid crystal active panel, in which 1 is an antenna, 2 is a receiver, 3 is a speaker, receiver 2 is a tuner 4, and an intermediate frequency amplification device. 5, video detection 6, audio demodulation circuit 7, etc.

The output of the video detection circuit 6 is branched to a synchronization circuit 8 including a synchronization separation and synchronization control circuit and a video amplification transistor 9.

The video amplification transistor 9 performs phase inversion of the video signal,
Analog signal switches 10 and 11 alternately switch normal and inverted video signals to drive a liquid crystal panel 13 via a buffer amplifier 12. 14 is a shift register for obtaining an X-axis drive signal for the liquid crystal panel 130, 15 is a shift register for Y-axis drive, and the shift register 13 includes analog switches 16cL, 16h, . . . 16rL'&
I[Next, the alternating video signal output of the buffer amplifier 12 is supplied to the data line of the active element in the panel 13.

The shift register 15 sequentially scans the control lines of the active elements within the panel 13. 1 and 7 are Ma I-I in the liquid crystal panel 13.
This is an example in which a pixel transistor, which is one of the active elements arranged in a J-square shape, is composed of Mo5-FET. The source of this transistor 17 is connected to the data line 18 on the X axis, and the gate is connected to the control line 19 on the Y axis.As a result, transistors are arranged in a matrix at the intersections of each data line and the control line.

A storage capacitor 21 is connected to each transistor in parallel with the pixel 20, as exemplified by the transistor 1T.
22 is a common electrode of liquid crystal pixels to which a constant DC voltage is applied. FIG. 2 shows details of the liquid crystal active panel drive circuit explained in FIG. 1, and 101 is a buffer amplifier; 102.10
3 is a power supply for the buffer amplifier 101, 104.105 is an analog switch switched by the X-axis shift register, 10
6. 107 is a pixel transistor switched by a Y-axis shift register, 10@-109 is a pixel, 110 is a common electrode of each pixel @ common electrode 110 is a buffer amplifier 101
Figure 3 is an example of an actual driving waveform of a liquid crystal active panel. α in Figure 3 is the video signal already mentioned in Figure 1, The figure shows a waveform V that is passed through a buffer amplifier that alternately switches the normal and inverted signals of the video signal, and by connecting a common electrode to the potential point 111, it is possible to prevent the DC component from being applied to the liquid crystal. It should be possible.

However, in reality, due to the asymmetric characteristics of the phase inversion transistor, changeover switch, buffer amplifier 101, etc., the integral average value of the neutral potential point 111 and the drive waveform V shown in FIG. 2 do not necessarily match. There are cases where a DC component is applied.

FIG. 4 shows an example of a driving circuit for a liquid crystal active panel according to the present invention, in which 201 is a buffer amplifier, 203 is a power supply for the buffer amplifier 201, and 204 and 205 are analog switches switched by an X-axis shift register. switch, 206.207
is a pixel transistor switched by a Y-axis shift register, 208 and 209 are pixels, and 210 is a common electrode of each pixel.

This common electrode 210 integrates the output 211 of the buffer amplifier with an integrating resistor 212 and an integrating capacitor 213, and applies a common potential via a voltage follower amplifier 214. Therefore, even if the output of the buffer amplifier 201 has an asymmetrical characteristic that depends on the amplitude of the amplifier, or there is a fluctuation in the DC component due to temperature fluctuations, the output of the voltage follower amplifier 214 will always be the same as that of the buffer amplifier 201. This is the integral average voltage of , and no DC component voltage is applied to the liquid crystal.

FIG. 5 shows another embodiment of the present invention, in which 30
1 is a buffer amplifier, 311 is the output of the buffer amplifier, which is supplied to each data line of the liquid crystal active panel via an analog switch, and an integrating resistor 312 and an integrating capacitor 31.
3 and supplies the output 314 of this integrated voltage directly to the common electrode of the liquid crystal active panel without going through a voltage follower amplifier.
If the value of is sufficiently small compared to the impedance of the common electrode of the panel, the simplified method shown in FIG. 4 is very effective.

As described above, according to the present invention, the voltage supplied to the common electrode of the liquid crystal active panel is the integrated voltage of a signal obtained by converting a video signal into an AC drive waveform, so that the DC voltage applied to the liquid crystal due to the asymmetrical characteristics of the AC drive signal, etc. A liquid crystal image display device that does not require the application of components can be realized.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a liquid crystal active panel television receiver, Figure 2 is an active panel drive circuit diagram, Figure 3a,
b is a drive waveform diagram, FIG. 4 is an active panel drive circuit diagram according to one embodiment of the present invention, and FIG. 5 is an active panel drive circuit diagram according to another embodiment of the present invention. 9... Video amplification transistor, 10.11... Analog switch, 12... Buffer amplifier, 22.110.210... Common electrode, 212.312
... Integrating resistor, 213.313... Integrating capacitor, 214... Voltage follower amplifier. (a)

Claims (1)

[Claims] In a liquid crystal display device in which active elements are arranged in an IJ box shape, a buffer amplifier for driving the liquid crystal, an integrating circuit for integrating the output of the buffer amplifier and a resistor and a capacitor are installed, and the integration circuit is An image display device characterized in that the integrated voltage of the circuit is the common electrode voltage of the liquid crystal display device.