JPS6161085B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal matrix display device, and more particularly to a liquid crystal matrix display device for displaying an image whose information is provided by a video luminance signal.

Currently, cathode ray tubes are a practical image display device for televisions and other devices, but due to their structure, display devices using cathode ray tubes have a large depth, and they also require a heater to generate electron beams to accelerate the electron beams. High voltage circuits, deflection circuits, etc. require large amounts of power. Recently, various matrix display devices using liquid crystals have been announced as thin, low power consumption display devices, but most of them digitally encode the video luminance signal, and each pixel is modulated according to the digital code by pulse width modulation. A method is used to control the brightness of the FIG. 1 shows an example of its configuration. The video luminance signal 8 is encoded by an analog-to-digital converter (hereinafter abbreviated as AD converter) 1 and transferred to a line memory 2 constituted by a shift register. In accordance with this data, the signal electrode drive circuit 3 drives the signal electrode 7 by performing operations such as pulse width modulation. FIG. 9 shows an example of a drive voltage waveform by pulse width modulation. a shows a voltage waveform applied to a certain scanning electrode, b shows a voltage waveform applied to a certain signal electrode, and c shows a driving voltage waveform of the liquid crystal in a pixel formed by the above-mentioned scanning electrode and signal electrode.

If we consider the case where a normal television image is displayed, the video luminance signal 8 is as shown in FIG. 2, and the horizontal scanning period 11 is approximately
The brightness information portion 12 excluding the blanking time is approximately 52.7 microseconds. If the number of signal electrodes is 100, then A-D converter 1
The data transfer rate from the line memory 2 to the line memory 2 has a period of about 527 nanoseconds, and the conversion time of the A/D converter 1 is required to be 527 nanoseconds or less. An A/D converter having such a conversion time is classified as a very high speed A/D converter according to current technology.

Next, as an example of a conventional liquid crystal matrix display device that does not use an AD converter, there is a system whose principle is shown in FIG. A voltage obtained by latching the luminance signal at a timing corresponding to each pixel is applied to the signal line 41, and the transistor 43 is sequentially activated by the scanning line 42.
When turned on, the capacitor 44 is charged with an amount of charge corresponding to the brightness of each pixel. The electrode of this capacitor 44 is formed so as to also serve as a liquid crystal driving electrode for each pixel to perform matrix display. However, this method requires a transistor to be placed for each pixel.
In particular, it is extremely difficult to obtain a matrix display device with a large number of pixels, such as a television, without defects.

An object of the present invention is to provide a liquid crystal matrix display device that displays an image given by a video luminance signal.
- Provide a simple electrode structure without using a D converter.

Next, the present invention will be explained according to one embodiment. In this example, a normal TV image is displayed,
A case where there are 48 scanning electrodes 6 and 64 signal electrodes 7 will be explained. FIG. 4 is a diagram showing the configuration of the present invention. The principle of the present invention is based on the fact that in a general matrix display, each signal electrode has a capacitance of several hundred pF or more relative to the entire scanning electrode via the liquid crystal, and the signal electrode itself has a capacitance of several hundred pF or more. It is intended to maintain the .

The amplifier circuit 21 has the configuration shown in FIG. 5, and the output level is centered around the non-selection voltage V ₂ of the scanning signals C ₁ to _{C 48} , and when applied directly to the signal electrode 7,
Amplitude suitable for matrix display using voltage averaging method
Variable resistors 24, 25, 26, so as to have V ₁ to _{V 3}
27. In addition, for alternating current driving of the liquid crystal, inverting and non-inverting signals of the video luminance signal 8 are sent to the switches 28 and 29 and the alternating current driving signal 3.
0 is selected as the signal electrode application signal 31.

Next _, in the switch section ₂₃ , as _shown in FIG _.
...... _d64 , and is turned ON and OFF sequentially in synchronization with the horizontal scanning of the television as shown in FIG. At this time, if the ON resistance of the switch is 100Ω and the capacitance of the signal electrode is about 1000pF, the time constant during charging is about 100 nanoseconds, and the signal is generated during the approximately 820 nanoseconds that one switch is ON. The electrodes are fully charged. Furthermore, with a time constant of this level, the number of signal electrodes can be increased to 527.
Also, during the period when the switch is OFF, the cycle is approximately 63.5 when charging is performed every horizontal scan of the TV.
microseconds, which is approximately 317 microseconds when charging is performed every matrix line scan. As mentioned earlier, the capacitance is several 100 pF, so turn the switch OFF.
If the impedance at the time is 1 MΩ or more, including the DC resistance of the liquid crystal itself, the potential of the signal electrode is maintained, and this level of impedance can be easily achieved.

Here, video signal 31, scanning signal c ₁ electrode S ₁
Switch control signal d ₁ to turn on, and electrode S ₁ and electrode
The relationship with the signal 53 applied to the intersection of _c1 is shown in FIG. That is, when SW ₁ is turned on by the switch control signal d ₁ , a voltage is applied to the electrode S ₁ at the moment when SW ₁ of the video signal 31 is turned on. This applied voltage time 51 is approximately 820+1
Seconds.

This voltage is held at electrode S ₁ until the next ON signal, and this holding time is approximately 63.5 microseconds.
In this embodiment, during the selection period of the scanning signal _c1 , the switch control signal _d1 is switched 5 times by the switch _SW1 .
Since it is turned on, the average voltage of five horizontal scans of the video signal 31 is applied to the liquid crystal. This means that there are 48 horizontal scanning electrodes C in this embodiment, and 48×5=
This is to accommodate the number of horizontal signals of the video signal 31, which is equivalent to 240 lines. In order to increase the horizontal resolution, the number of electrodes C may be increased and the selection period of the scanning signal _c1 may be shortened.

Further, another embodiment is shown in FIG. In this example, an image is displayed by retaining the video luminance signal 8 as an analog quantity in the analog memory section 13 and applying it to the signal electrode 7. The analog memory section 13 forms a so-called sample hold circuit with a sampling switch 15, a capacitor 16, and a buffer amplifier 17, and the sampling switch 15 is turned on and off by a control signal 14 generated by the control circuit 8. According to this example:
Compared to the previous embodiment, the sampling switch 15
The voltage applied to the signal electrode is the same when it is ON, but the voltage applied to the signal electrode is stable when it is OFF.

As described above, according to the present invention, an image can be displayed on a liquid crystal matrix display device from a video luminance signal without using an expensive and power-consuming A-D converter, and with a simple electrode structure. A display device can be realized.

As described above, in the present invention, a liquid crystal is sealed between a pair of substrates, a plurality of scanning electrodes and a plurality of signal electrodes are formed in a matrix on one or both of the substrates, and each scanning electrode and In a liquid crystal display device in which a pixel electrode is formed at the intersection with each signal electrode, a sampling means is provided that samples a video signal in time series for each scanning signal applied to each scanning electrode and supplies it to the signal electrode. The signal electrode is charged with the video signal when the sampling means is in the ON state, and the potential of the video signal is held when the sampling means is in the OFF state. Even if the display device consists of the following, reliable image display can be obtained with a simple electrode structure.

[Brief explanation of the drawing]

Fig. 1 shows the configuration of a liquid crystal matrix display device using an A-D converter, Fig. 2 shows a video luminance signal, Fig. 3 shows an embodiment of the present invention using an analog memory, and Fig. 4 shows the structure according to the present invention. A configuration example of a liquid crystal matrix display device, FIG. 5 shows a specific example of the amplifier circuit 21, FIG. 6 shows a specific example of the switch section 23, and _{FIG .} relationship,
FIG. 8 shows the signal electrode applied signal 31 and the scanning signal C ₁ ~
Relationship with C ₄₈ , Figure 9 is an example of a drive waveform by pulse width modulation, Figure 9a is a scanning voltage waveform, Figure 9b is a signal voltage waveform, Figure 9c is a voltage waveform applied to the liquid crystal, Figure 9c is a voltage waveform applied to the liquid crystal, The figures each show a principle diagram of a system in which charging is performed using a transistor added to each pixel and matrix display is performed. FIG. 11 is a waveform diagram showing the relationship between the video signal, the scanning signal, and the liquid crystal application signal. 1...A-D converter, 2...Line memory, 3
...Signal electrode drive circuit, 4...Scanning electrode drive circuit, 5...Control circuit A, 6...Scanning electrode, 7...
Signal electrode, 8...Video luminance signal, 9...Synchronization signal, 11...Horizontal scanning period, 13...Analog memory section, 18...Control circuit B, 21...Amplification circuit, 22...Control circuit C, 23...Switch part.

Claims (1)

[Claims] 1 A liquid crystal is sealed between a pair of substrates, a plurality of scanning electrodes and a plurality of signal electrodes are formed in a matrix on one or both of the substrates, and the intersections of each scanning electrode and each signal electrode are formed on one or both of the substrates. A liquid crystal display device in which pixel electrodes are formed includes a sampling means for sampling a video signal in time series for each scanning signal applied to each scanning electrode and supplying the sampled signal to the signal electrode. The liquid crystal display device is characterized in that the video signal is charged when the sampling means is in an ON state, and the potential of the video signal is held when the sampling means is in an OFF state.