Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-10-26
2001-02-20
Wu, Xiao (Department: 2774)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S098000, C345S097000
Reexamination Certificate
active
06191771
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a liquid crystal display, such as a liquid crystal display panel or a liquid crystal optical shutter array, that contains a matrix array of pixels having a liquid crystal layer consisting of a liquid crystal that exhibits a smectic phase.
BACKGROUND ART
Ferroelectric liquid crystals and antiferroelectric liquid crystals are generally known liquid crystals that exhibit smectic phases. These liquid crystals are used in image-producing displays by utilizing the properties that both types of liquid crystals possess spontaneous polarization, and that the direction of the spontaneous polarization changes under the influence of an external electric field. Liquid crystal panels using antiferroelectric liquid crystals, for example, have been researched vigorously since it was reported in Japanese Patent Unexamined Publication No. 2-173724 by Nippondenso and Showa Shell Sekiyu that such liquid crystal panels provided wide viewing angles, were capable of fast response, and had good multiplexing characteristics.
However, when a still image or the like is displayed on an antiferroelectric liquid crystal display with the same image pattern staying on the display 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 visible on the screen (this phenomenon is hereinafter called the “burn-in phenomenon”). This burn-in phenomenon is believed to be caused by the fact that antiferroelectric liquid crystals have a layer structure.
It is also known that, in ferroelectric liquid crystal displays using ferroelectric liquid crystals, a similar burn-in phenomenon occurs when the same pattern such as a still image has been displayed on the screen for a long period of time. This burn-in, unlike the case of antiferroelectric liquid crystals, is believed to be caused by the movement of impurity ions contained in the liquid crystal cell. Ferroelectric liquid crystals have a spontaneous polarization, and when an external voltage is 0 V, an internal electric field due to the spontaneous polarization is always present in a direction perpendicular to the liquid crystal cell. Impurity ions in the liquid crystal cell move toward the cell-substrate interface in such a manner as to cancel the internal electric field, and an ion electric field due to the impurity ions occurs in a direction opposite to the direction of the internal electric field. If this condition continues for a long period of time, the impurity ions are adsorbed onto the cell-substrate interface. As a result, the ion electric field persists after the internal electric field due to the spontaneous polarization is removed. This is believed to cause the burn-in phenomenon.
DISCLOSURE OF THE INVENTION
Accordingly, an object of the present invention is to resolve the above-outlined problems and provide a liquid crystal display capable of producing a high contrast display. To achieve this, in a liquid crystal display using an antiferroelectric liquid crystal, the change of the layer structure due to continuous driving is corrected to alleviate the burn-in phenomenon caused by differences in the way that the layer structure changes. Further, in a liquid crystal display using a ferroelectric liquid crystal, the burn-in phenomenon is likewise alleviated by not allowing the internal electric field due to the spontaneous polarization occurring in the same direction to remain for too long a period.
To accomplish the above object, the liquid crystal display of the present invention, which contains a plurality of pixels arranged in a matrix pattern and having, between a pair of substrates, a liquid crystal exhibiting a smectic phase, comprises means for generating display data to write to the pixels, and means for forcibly setting random pixels of the plurality of pixels in a prescribed display state for a prescribed period regardless of the display data, the random pixels being distributed throughout the matrix pattern.
To describe the invention in more detail, the liquid crystal display of the present invention is a liquid crystal display that contains a plurality of pixels arranged in a matrix pattern and having, between a pair of substrates, a liquid crystal exhibiting a smectic phase, the substrates having a plurality of scanning electrodes and signal electrodes, respectively, and comprises: a display data generating circuit for generating display data to write to the pixels; a scanning voltage generating circuit for generating, based on the display data from the display data generating circuit, a scanning voltage to be applied to the scanning electrodes; a signal voltage generating circuit for generating, also based on the display data from the display data generating circuit, a signal voltage to be applied to the signal electrodes; and a display data conversion circuit for converting the display data in order to forcibly set random pixels of the plurality of pixels in a prescribed display state for a prescribed period regardless of the display data, the random pixels being distributed throughout the matrix pattern.
The display data conversion circuit is provided between the display data generating circuit and the signal voltage generating circuit, and has a function to designate the pixel whose display data is to be converted or a function to randomly determine the pixel whose display data is to be converted.
The display data conversion circuit also has a function to set the interval at which the display data is converted to an arbitrary value or a function to automatically change the display data conversion interval.
Further, the display data conversion circuit has a function to arbitrarily set the number of pixels per scanning line whose display data is to be converted forcibly or a function to automatically change the number of pixels per scanning line whose display data is to be converted forcibly.
Furthermore, the display data conversion circuit has a function to set the level of the prescribed display state, to which the conversion is to be made, to an arbitrary level, and to automatically change this level.
ADVANTAGEOUS EFFECTS OF THE INVENTION
When a display is produced on a liquid crystal display using the present invention, differences between display pixels in the way that the layer structure changes can always be eliminated, or the occurrence of the internal electric field due to the spontaneous polarization can be held within a short period of time; this alleviates the burn-in phenomenon and provides a good display with no degradation in display quality.
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Citizen Watch Co. Ltd.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Wu Xiao
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