JPH04100091A - Active matrix type liquid crystal display device - Google Patents

Abstract

PURPOSE:To clearly display the contour part of an image by sampling/holding the input of a video signal with a sampling signal with a thin pulse width which is equal to or under 1/2 of one picture element selection term. CONSTITUTION:A timing generator 1 generates a digital signal for driving a horizontal shift register 2 and a vertical shift register 3 in synchronism with a synchronizing signal included in the video signal. Furthermore, the sampling signal with the pulse width which is equal to or under 1/2 of one picture element selection term is generated in synchronism with a horizontal shift register driving pulse. In a sample-and-hold circuit 8, a switch is turned on/off with the sampling signal outputted from the generator 1 and the video signal is sampled. The video signal after performing sample-hold is written in a corresponding liquid crystal display as it is. As the result of display, even when the contour part of the video signal is not equivalent to a switching point for selecting a picture element, a part at a medium level(gray) is not generated and the contour is clearly reproduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving an active matrix liquid crystal display device.

[Prior Art] FIG. 2 shows a configuration diagram of a conventional active matrix type liquid crystal display device. In FIG. 2, I is a timing generator, 2 is a horizontal shift register, 3 is a vertical shift register, 4 is a horizontal transistor, 5 is a pixel transistor, 6 is a liquid crystal, and 7 is a video signal input. Horizontal shift register 2
is operated by a signal from the timing generator 1, and turns on the horizontal transistors 4 sequentially from left to right. The vertical shift register 3 is similarly operated by the timing generator 10' signal, and sequentially turns on the pixel transistors 5 from bottom to top. The video signal passes through the selected horizontal transistor 4, further passes through the selected pixel transistor 5, and is written to the liquid crystal 6. The operation of the vertical shift register 3 is such that when the horizontal shift register 2 sequentially selects all the horizontal transistors 4 from left to right once, the next column (one column above) is selected.
pixel transistor 5 is selected. In this way, a two-dimensional image is displayed by sequentially writing video signals to the liquid crystal corresponding to all pixels.

[Problem to be Solved by the Invention 1] However, the above-mentioned conventional technology has a problem in that the reproducibility of the ringed portion of the image is poor. FIG. 3 shows a timing diagram of a conventional active matrix type liquid crystal display device.

In FIG. 3, 9 is one pixel y selection time, 10 is a video signal,
11 is the display result. Video signal 10 and display result 11
High level indicates white and low level indicates black. If the circular part of the video signal 10 (the switching point between white and black, and between black and white) matches the switching point of pixel selection, the display result] is as follows.
The hoop is reproduced (part a in Figure 3), but the intermediate level (gray) area is the origin of the occurrence, and the reproduction of the hoop is poor (part a in Figure 3). In a conventional active matrix liquid crystal display device, the video signal is sampled with a sampling width of one pixel selection period, so the video signal is averaged over one pixel selection period.

As a result, if the hoop is within the middle of the pixel selection time, an intermediate level (gray) will be displayed.

SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and its purpose is to provide an active matrix liquid crystal display device that can clearly display the ringed portions of images. Means] The active matrix liquid crystal display device of the present invention includes:
a timing generator that generates a sampling signal with a pulse width of 1/2 or less of one pixel selection period in synchronization with a horizontal shift register drive pulse; and a sample hold circuit that samples and holds a video signal input using the sampling signal. It is characterized by having the following.

[Function] According to the above configuration of the present invention, the video signal input is sampled and held using a sampling signal with a narrow pulse width of 1/2 or less of the pixel selection period, and the result is written to each pixel. Middle level (gray) in the ring section of
There are fewer occurrences of , and a clear image is displayed.

[Example 1] FIG. 1 is a block diagram of an active matrix type liquid crystal display device according to the present invention, in which 1 is a timing generator;
8 is a sample hold circuit, and 2 to 7 have the same structure and names as in FIG. A timing generator 1 generates a digital signal for driving a horizontal shift register 2 and a vertical shift register 3 in synchronization with a synchronization signal included in a video signal. Furthermore, among the above-mentioned digital signals, in synchronization with the horizontal shift register drive pulse, -1 of the pixel selection period is
Generates a sampling signal with a pulse width of /2 or less.

The sample and hold circuit 8 is composed of a switch and a holding capacitor. The switch is turned on or off by the sampling signal output from the timing generator 1, and samples the video signal.

The above situation will be explained with reference to FIG. 4, a timing diagram of the active matrix type liquid crystal display device according to the present invention. Fourth
In the figure, 9 is one pixel selection period, 10 is a video signal, 1
Reference numeral 2 indicates a horizontal shift register driving pulse 13 as a sampling pulse, 14 indicates a video signal after sample and hold, and 15 indicates a display result.

The sampling pulse 13 is synchronized with the horizontal shift register driving pulse 12 and is generated at the beginning of the one pixel selection period 9 with a pulse width less than 1/2 of the one pixel selection period 9 . The video signal 10 is sampled and held by the sample and hold circuit 8 (sampled at the high level of the sample pulse 13 and held at the low level), and the video signal 14 after sampled and held is sampled and held at the low level of the sample pulse 13.
Outputs the signal shown in The video signal 14 after sample and hold is written as it is to the liquid crystal corresponding to each pixel.

Now, if we compare it with the conventional timing chart for District 3,
As a display result, even if the hoop portion of the video signal 10 does not coincide with the pixel selection switching point, no intermediate level (gray) portion occurs and the hoop is clearly reproduced. You can see that

Good results cannot be obtained unless the width of the sampling pulse 13 is 1/2 or less of one pixel selection period. In addition, the narrower the width, the better the results obtained.9 The timing generator 1 is realized by an integrated circuit (IC) composed of C-MOS l-ransis or the like. Sampling pulse 13 is horizontal shift register drive pulse 12
It is generated by mono-multi-by-break using human power.

The sample and hold circuit is a transistor or FET
It consists of an analog switch and a ceramic capacitor.

[Effect of the invention 1 As described above, according to the present invention, the video signal input is sampled in a short period of 1/2 or less of one pixel selection period,
Since a hold signal is written during this period, there is less occurrence of intermediate level (gray) portions in the ring portion of the image, making it possible to provide an active matrix type liquid crystal display device that displays a clear image. It has this effect.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an active matrix type liquid crystal display device according to the present invention. FIG. 2 is a configuration diagram of a conventional active matrix type liquid crystal display device. FIG. 3 is a timing diagram of a conventional active matrix type liquid crystal display device. FIG. 4 is a timing diagram of an active matrix type liquid crystal display device according to the present invention. Timing generator/Horizontal shift register/Vertical shift register...Horizontal transistor/Pixel transistor...Liquid crystal...Video signal input...Sample and hold circuit Pixel selection time Video signal/Display result 13 ・ 14 ・ v ・・Horizontal transistor Drive pulses, sampling pulses, video signals after sample hold, and above display results Applicant Seiko Epson Co., Ltd. Agent Patent attorney Kizobe Suzuki (and 1 other person) Figure 1 Figure 3

Claims (1)

[Claims] (1) a) In an active matrix liquid crystal display device that displays a two-dimensional image, b) Generating a sampling signal with a pulse width of 1/2 or less of one pixel selection period in synchronization with a horizontal shift register drive pulse. 1. An active matrix type liquid crystal display device comprising: a timing generator; and c) a sample and hold circuit that samples and holds a video signal input using the sampling signal.