Computer graphics processing and selective visual display system – Display peripheral interface input device – Light pen for fluid matrix display panel
Reexamination Certificate
1997-10-06
2001-05-29
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Light pen for fluid matrix display panel
C345S089000, C345S182000, C345S182000, C345S208000
Reexamination Certificate
active
06239781
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a circuit for generating a gray-scale signal of the pulse-width modulation type, and to a matrix-addressed liquid crystal display employing this circuit.
In many liquid crystal displays, each picture element has only on and off states, so intermediate gray levels are displayed by switching the picture element on and off repeatedly arid controlling the on-off duty cycle. This technique is known as frame rate control, or more generally as pulse-width modulation. In a color display, such as a color liquid crystal television set, this technique can be used to display a large number of colors by mixing different intensities or red, blue, and green. The term ‘gray scale’ is commonly employed to denote these intensities, even though color is involved. Liquid crystal television sets employ matrix addressing, in which the picture elements on the display screen are scanned a line at a time.
A problem that arises is that to display the large number of gray levels needed for a natural display appearance, the interval of time during which a picture element is scanned must be finely divided, requiring a high-frequency timing clock signal. The use of a high-frequency clock signal increases the power dissipation of the display. In addition, the liquid crystal material must be capable of responding to voltage changes at speeds comparable to the speed of the timing clock signal, but liquid crystal materials with very fast response times are not easy to find.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to reduce the frequency of the timing clock signal needed for generating a gray-scale signal by pulse-width modulation.
A further object of the invention is to avoid causing flicker.
A gray-scale signal generated according to the present invention represents a gray level of a picture element in an image that is displayed in successive frames, the picture element being scanned during a certain interval in each frame. Each of these intervals is divided into a first number of parts. A waveform is generated as a set of waveform parts for these intervals in a second number of frames the set of waveform parts, having either a high level or a low level in each waveform part of each interval in each frame. The set of waveform parts covers a total number of parts equal to the first number multiplied by the second number. Among this total number of parts, the waveform parts are high for a number of parts that is variable in steps of one part and responsive to the gray level of the picture element. The gray-scale signal is generated from this waveform as a set of waveform parts.
When the invented method is applied to drive multiple picture elements in a display, the timing of the gray-scale signals is varied so that, even if a certain number of side-by-side picture elements have identical gray levels, their gray-scale signals have waveforms that do not all go high and low in unison.
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English Language Abstract of Japanese Patent Application No. 04287584, Oct. 13, 1992.
Kovalick Vincent E.
OKI Electric Industry Co., Ltd.
Shalwala Bipin
Wenderoth Lind & Ponack, LLP.
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