Computer graphics processing and selective visual display system – Display driving control circuitry
Reexamination Certificate
1997-12-26
2001-01-30
Saras, Steven J. (Department: 2775)
Computer graphics processing and selective visual display system
Display driving control circuitry
C345S003100, C345S182000
Reexamination Certificate
active
06181330
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to video display devices for sampling and displaying the video output signal from signal sources such as computers, and more specifically, to horizontal display width adjustment circuits and vertical display width adjustment circuits which allow the width of the display screen to be adjusted as required to overcome timing incompatibility between the input video signal and the predetermined effective screen area. The present invention is further related to a liquid crystal video display device employing these width adjusting circuits.
BACKGROUND OF THE INVENTION
The phase difference between the horizontal and vertical synchronizing signals and video signals produced from signal sources such as computers generally vary according to the signal source. The number of picture elements per horizontal scanning period and the number of lines per vertical scanning period of the video signal produced from the signal source also vary.
To enable the display of a wide variety of signals as mentioned above on a video display device, display elements for one picture element of the signal source are conventionally displayed having a picture element : display element ratio of 1 : 1 or 1: integer.
If the number of picture elements in the signal source is less than the number of display elements of the video display device and the picture elements are displayed in a one to one ratio, the display width of that signal source becomes smaller than the displayable screen area. Similarly, if the number of picture elements in the signal source is less than the number of display elements of a video display device and the picture elements are displayed in a one to integer ratio, the image width may become wider than the displayable screen area.
As described above, the prior art may display the video image of the signal source at a narrower width than the displayable screen area of the video display device depending on the video output signal from the computer when video output signals from different models of computer are displayed in a one to one ratio (the ratio of the number of picture elements in the signal source to the number of display elements).
In addition, the video image of the signal source may become wider than the displayable screen area of the video display device in the prior art, depending on the video output signal from the computer, when video output signals from different models of computers are displayed in a one to integer ratio (the ratio of the number of picture elements in the signal source to the number of display elements). As a result, the user may not be able to see part of the video image, and may need to adjust one or both of the horizontal and vertical screen positions to see the missing portion of the video image.
SUMMARY OF THE INVENTION
A display width adjusting circuit of the present invention comprises a key circuit for requesting expansion and compression of horizontal and vertical display areas, a microcomputer for detecting the on and off states of the key circuit and also detecting horizontal and vertical synchronizing signal frequency of the input video signal, a PLL circuit which receives the setting for the frequency division ratio from the microcomputer, an A/D converter which receives the analog video signal and is controlled by the PLL circuit under the control of the microcomputer, and a scan converter which receives the output signal from the A/D converter, horizontal and vertical synchronizing signals, and the clock signal from the PLL circuit, and is controlled by the microcomputer for outputting the video signal which can be displayed in a required size of display image on a required area of the screen of a video display device.
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Shindo Yoshikuni
Torii Hiromitsu
Yui Hirokatsu
Matsushita Electric - Industrial Co., Ltd.
Mengisteab Tewolde
Ratner & Prestia
Saras Steven J.
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