Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-11-09
2002-01-15
Mengistu, Amare (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S094000, C349S174000
Reexamination Certificate
active
06339416
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an antiferroelectric liquid crystal display, such as a liquid crystal display panel or a liquid crystal optical shutter array, having a liquid crystal layer of antiferroelectric liquid crystal, and a method of driving the same.
BACKGROUND ART
Liquid crystal panels using antiferroelectric liquid crystals have been researched extensively since it was reported in Japanese Patent Unexamined Publication No. 2-173724 by Nippondenso and Showa Shell Sekiyu that such liquid crystal panels provide wide viewing angles, are capable of fast response, and have good multiplexing characteristics.
The conventional art driving method, however, has had the problem that after the same image pattern has been displayed for a long period of time, when a different image pattern is displayed on the screen, the previously displayed image remains slightly visible on the screen (this phenomenon is hereinafter called the “image sticking phenomenon”).
It is believed that this phenomenon occurs because an antiferroelectric liquid crystal cell is formed in a smetic layer structure and the amount of light transmitted through the liquid crystal panel varies depending on the geometry of the layer structure. To prevent this image sticking phenomenon, it has been proposed to apply a layer structure controlling voltage waveform each time the layer structure changes. For example, Japanese Patent Unexamined Publication No. 6-202078 discloses a configuration in which, in addition to the usual display driving circuit, a layer structure controlling voltage waveform circuit is provided which applies a layer structure controlling voltage waveform to the liquid crystal panel.
However, since the layer structure controlling voltage waveform differs in frequency and peak value from the display driving voltage waveform, the layer structure controlling voltage waveform circuit, including a clock generating circuit, voltage value conversion circuit, etc., needs to be provided separately from the display driving circuit. As a result, two circuits, i.e., the display driving circuit and the layer structure controlling voltage waveform circuit, must be provided for one liquid crystal display, which not only increases the size and complexity of the liquid crystal display circuitry but also leads to higher manufacturing costs.
It is, accordingly, an object of the present invention to provide an antiferroelectric liquid crystal display that is compact in construction and inexpensive to manufacture by using a display driving circuit adapted to output a layer structure controlling voltage waveform and thereby eliminating the need to provide a layer structure controlling voltage waveform circuit separately. It is also an object of the present invention to provide a method of driving such an antiferroelectric liquid crystal display.
DISCLOSURE OF THE INVENTION
After studying the display driving voltage waveform and layer structure controlling voltage waveform for antiferroelectric liquid crystal, it has been discovered that if the display driving voltage waveform is set so that the peak value of the scanning voltage applied during the non-selection period becomes equal to the peak value of the voltage applied during the selection period, a voltage waveform close to the optimum layer structure controlling voltage waveform can be obtained.
In view of this, to achieve the above object, in the present invention, the display driving voltage waveform is set so that the peak value of the scanning voltage waveform applied during the selection period becomes equal to the peak value of the scanning voltage waveform applied during the non-selection period, and the thus set display driving voltage waveform is output as a layer structure controlling voltage waveform, not as a display driving voltage waveform, from the display driving circuit for a optional length of time for application to the liquid crystal.
Further, the liquid crystal panel includes a temperature sensor and, in accordance with the information output from the temperature sensor, the display driving voltage waveform in which the peak value of the scanning voltage waveform applied during the selection period is set equal to the peak value of the scanning voltage waveform applied during the non-selection period is output as the layer structure controlling voltage waveform for the optional length of time.
Alternatively, the display driving voltage waveform with both peak values set equal is output as the layer structure controlling voltage waveform for optional length of time at predetermined intervals of time.
Preferably, the display driving voltage waveform has a reset period preceding the selection period.
ADVANTAGEOUS EFFECT OF THE INVENTION
According to the present invention, in the display driving voltage waveform, the peak value of the voltage waveform applied during the selection period is set equal to the peak value of the voltage waveform applied during the non-selection period. By using this waveform as the layer structure controlling voltage waveform, it becomes possible to reduce the “image sticking phenomenon” without providing a separate layer structure controlling voltage waveform circuit and to produce a good display without degrading the display quality. Furthermore, an antiferroelectric liquid crystal display, which is compact and inexpensive compared with the conventional art, can be realized.
Furthermore, since the temperature sensor is provided so that the layer structure controlling voltage waveform is applied at appropriate timing, the “image sticking phenomenon” can be reduced in a reliable manner.
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Citizen Watch Co. Ltd.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Mengistu Amare
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