Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-05-12
2001-03-20
Hjerpe, Richard A. (Department: 2774)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C345S090000, C345S208000
Reexamination Certificate
active
06204835
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to drive schemes for liquid crystal displays employing cholesteric, reflective bistable liquid crystal material. In particular, the present invention relates to a drive scheme for cholesteric liquid crystal material that drives the liquid crystal material between a reflective planar texture and a non-reflective focal conic texture. Specifically, the present invention is directed to a drive scheme which repeatedly applies a series of two pulses with a relaxation time between each series so as to incrementally change the appearance of the liquid crystal material.
BACKGROUND ART
Drive schemes for cholesteric materials are disclosed in U.S. patent application Ser. No. 08/852,319, which is incorporated herein by reference. As discussed therein, a two phase drive scheme may be employed to completely drive the cholesteric liquid crystal material from one texture to another. This drive scheme, although simple in application requires the use of relatively long duration pulses with a large magnitude for the preparation and selection phases. As a result, use of the disclosed two phase drive scheme generates a flicker when operative at a video rate frequency. Moreover, the disclosed two phase drive scheme requires high voltage application and therefore costlier drive circuits.
Based upon the foregoing, it is evident that there is a need in the art for a drive scheme which is simple yet employs lower voltage values to attain the desired texture. Moreover, there is a need in the art for a simple two phase drive scheme which is suitable for video rate operation.
DISCLOSURE OF INVENTION
In light of the foregoing, it is a first aspect of the present invention to provide a cumulative two phase drive scheme for a bistable cholesteric reflective display.
Another aspect of the present invention is to provide a cholesteric liquid crystal display cell with opposed substrates, wherein one of the substrates has a plurality of row electrodes facing the other substrate which has a plurality of column electrodes, and wherein the intersections between the row and column electrodes form picture elements or pixels.
Yet another aspect of the present invention, as set forth above, is to provide a cumulative two phase drive scheme which repeats a series of two voltage applications to incrementally change the texture of the liquid crystal material between focal conic and planar textures as well as change the reflectance of the cholesteric material.
A further aspect ofthe present invention, as set forth above, is to provide a cumulative two phase drive scheme wherein a first phase of the series applies a preparation voltage and a second phase of the series applies a selection voltage, whereupon the material is allowed to relax and then the two phases are reapplied to the liquid crystal material.
Yet a further aspect of the present invention, as set forth above, is to apply a high selection voltage to the liquid crystal material which causes an incremental change in the appearance thereof and wherein repeated applications of the high selection voltage drives the material toward a planar texture.
Yet an additional aspect of the present invention, as set forth above, is to apply a low selection voltage to the liquid crystal material which causes an incremental change in the appearance thereof and wherein repeated applications of a low selection voltage drives the material toward a focal conic texture.
The foregoing and other aspects ofthe present invention which shall become apparent as the detailed description proceeds are achieved by a method of addressing bistable liquid crystal material disposed between opposed substrates, and wherein one of the substrates has a first plurality of electrodes facing a second plurality of electrodes on the other substrate, wherein the intersection of the first and the second plurality of electrodes forms a plurality of pixels, the method comprising the steps of: a) applying a preparation voltage across the first and second plurality of electrodes; b) subsequently applying a selection voltage across the first and second plurality of electrodes; and c) repeating steps a) and b) until the material exhibits a desired reflectance.
Other aspects of the present invention are obtained by a method of addressing a cell of bistable cholesteric liquid crystal material disposed between opposed substrates, wherein one of the substrates has a plurality of row electrodes facing a plurality of column electrodes on the other substrate, and wherein intersections of the row and the column electrodes form a plurality of pixels on the cell, the method comprising the steps of: applying a preparation voltage to one of said row electrodes and said column electrodes; applying a portion of said selection voltage to one of said row electrodes and said column electrodes while applying a remaining portion of the selection voltage to the other of said row electrodes and said column electrodes; allowing the material to relax; and repeating said applying and said allowing steps until the material is driven to a desired texture.
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Kozachenko et al.,Hysteresis as a Key Factor for the Fast Control of Reflectivity in Cholesteric LCDs,1997 SID, pp. 148-151.
Yang Deng-Ke
Zhu Yang-Ming
Dinh Duc
Hjerpe Richard A.
Kent State University
Renner Kenner Greive Bobak Taylor & Weber
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