Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Patent
1996-08-16
2000-04-18
Brier, Jeffery
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
G09G 336
Patent
active
060521066
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention broadly relates to liquid crystal matrix panels and more particularly it refers to a control method for matrix panels of a direct addressing, ferroelectric liquid crystal (FLC) type, to enable their improved operation.
2. Description for the Related Art
As it is known, the panels to which this invention relates are used in devices for displaying images and for optical computation applications, both of the projection and of the direct vision types. In these devices, each picture element (pixel) ideally corresponds to the intersection of an element of a first electrode set (for instance arranged as rows) and an element of a second electrode set (for instance arranged as columns) and materially it corresponds to an electro-optical cell comprising a ferroelectric liquid crystal in the room existing between two facing electrodes belonging to the above mentioned two electrode sets. In usual arrangements, a pair of crossed polarisers operatively completes the cell and makes visible the orientation changes of the director in the liquid crystal that can be of the smectic C chiral type.
The panel consisting of FLC cells can be electrically controlled according to various addressing modes (or schemes) or modes for applying voltages and currents to the two electrode assemblies, so as to determine the states of all cells, the number of which is usually much higher than the number of electrodes. The main object of this invention is to provide a novel addressing method as hereinafter disclosed.
The device as a whole comprises the assembly of the described panel with the related electronic circuitry to generate the various voltage signals needed for its operation and the interconnection elements to the panel electrodes. According to the expected application, in addition, polarisers, colour filters, light sources and an optical system can be provided therein.
This invention additionally consists in the device comprising the above set forth assembly and operating according to the hereinafter described control method.
More precisely, this invention relates to a directly addressed FLC matrix panel wherein the ferroelectric liquid crystal cells operate according to a bistable or multistable behaviour in the absence of voltage or in the presence of a continuously applied, high frequency voltage having a sufficient and suitable rms amplitude, known as a high frequency or alternated current stabilisation voltage. As it will be explained, such a role can be played by the control voltages used, in particular, by the data voltages.
Under the term high frequency stabilisation, the phenomenon is usually meant where the stable states of a cell, when a high frequency voltage is present, are closer to the states that can be achieved by the continuous application of a dc voltage. A broader meaning is allotted in this patent description to the above term, since it also includes the phenomenon according to which the relaxation of a cell to a stable state becomes faster when a high frequency voltage is present.
The ferroelectric liquid crystal can be of the smectic C chiral type and the cells can be of the chevron type or of the partially or totally straightened up chevron type. In both cases, the smectic layers are approximately broken up into two halves, which are tilted in opposite directions with respect to a line normal to the cells, at an angle almost equal to (between 110% and 75% in the first case) or much smaller than (between 0% and 75% in the latter case) the characteristic angle of the SmC phase. Multi-stable behaviours can be related to microdomain mixtures of a number of stable states and the crystal can be utilised for storage of intermediate shades. Reference is made, for instance to P. Maltese, "Advances and problems in the development of ferroelectric liquid crystal displays", in Molecular Crystals and Liquid Crystals, Gordon and Breach, vol. 215, pages 57 and following and to the references cited therein.
By means of spaced apart rectangular pulses, of a
REFERENCES:
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patent: 5594464 (1997-01-01), Tanaka et al.
patent: 5684503 (1997-11-01), Nomura et al.
SID International Conference 1993, Digest of Technical papers, 1993, pp. 642-645, P. Maltese et al. "Superfast Addressing Modes for SSFLC Matrix Displays".
Liquid Crystals, 1993, pp. 819-834, P. Maltese et al., "An Addressing Effective Computer Model for Surface Stabilized Ferroelectric Liquid Crystal Cells".
IBM Technical Disclosure Bulletin, vol. 36, No. 1, Jan. 1993, pp. 446-447, "Three-Slot Drive Scheme for Multiplexing of Ferroelectric Liquid-Crystal Shutter Devices".
Brier Jeffery
Universita Degli Studi Di Roma Sapienza
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