Liquid crystal cells – elements and systems – With specified nonchemical characteristic of liquid crystal... – Within smectic phase
Reexamination Certificate
1999-05-24
2002-04-09
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
With specified nonchemical characteristic of liquid crystal...
Within smectic phase
C349S072000
Reexamination Certificate
active
06369872
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, that has a liquid crystal layer consisting of antiferroelectric liquid crystal.
BACKGROUND ART
Liquid crystal panels using antiferroelectric liquid crystals have been researched vigorously since it was reported in Unexamined Japanese Patent 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 prior art driving method, however, has had the problem that when the same image pattern has been displayed for a long period of time, a phenomenon occurs in which, 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”).
This phenomenon is believed to be caused by the property that antiferroelectric liquid crystals form a layer structure within a cell, with the way the layers bend being different depending on the display state (i.e. whether it is a white display state or a black display state). To alleviate this phenomenon, Unexamined Japanese Patent Publication No. 6-202078 proposes a liquid crystal display which includes, in addition to the display driving circuit, a layer structure control voltage waveform circuit capable of applying a layer structure control voltage waveform to the panel.
This prior art device, however, requires that the layer structure control voltage waveform be applied in every predetermined period (for example, every frame period or every scanning period). Since images different from the display image are displayed frequently, degradation of display quality has been a problem.
It is, accordingly, an object of the present invention to provide an antiferroelectric liquid crystal display that alleviates the image-sticking phenomenon without degrading the display quality.
DISCLOSURE OF THE INVENTION
To achieve the above object, the present invention provides the following configuration.
The antiferroelectric liquid crystal display of the invention includes a temperature sensor for measuring the temperature of a liquid crystal panel, a heater for heating the liquid crystal panel, and a heater control circuit for controlling the temperature of the liquid crystal panel, wherein the liquid crystal panel, while being driven to display, is constantly maintained at a temperature at which the smectic layer spacing in an antiferroelectric liquid crystal material, sandwiched within the liquid crystal panel, becomes the smallest.
In the above antiferroelectric liquid crystal, when the temperature of the liquid crystal panel, after power on, has reached the temperature at which the smectic layer spacing in the antiferroelectric liquid crystal material becomes the smallest, a layer structure control voltage waveform is applied to the liquid crystal panel. The layer structure control voltage waveform is also applied to the liquid crystal panel when the temperature of the liquid crystal panel has changed during a display and has thereafter been brought back to the temperature at which the smectic layer spacing in the antiferroelectric liquid crystal material becomes the smallest.
The antiferroelectric liquid crystal display further includes a layer structure control voltage waveform circuit for generating the layer structure control voltage waveform and a voltage waveform control circuit for controlling timing and the temperature of the liquid crystal panel when the layer structure control voltage waveform is to be applied to the liquid crystal panel.
The antiferroelectric liquid crystal display further includes means for blocking light from a backlight in the antiferroelectric liquid crystal display when the layer structure control voltage waveform is applied to the liquid crystal panel.
The antiferroelectric liquid crystal display further includes means for monitoring the polarization reversal current of the liquid crystal display, and for detecting the temperature of the liquid crystal panel from the value of this current, instead of detecting the temperature using the temperature sensor.
With the above configuration, the image sticking phenomenon can be alleviated without degrading the display quality.
REFERENCES:
patent: 5119219 (1992-06-01), Terada et al.
patent: 5316694 (1994-05-01), Murashiro et al.
patent: 5393460 (1995-02-01), Okabe et al.
patent: 5781266 (1998-07-01), Nakao et al.
patent: 5798814 (1998-08-01), Konuma
patent: 5929833 (1999-07-01), Kobshobu et al.
Citizen Watch Co. Ltd.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Parker Kenneth
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