Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-05-12
2001-07-31
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S094000, C345S087000, C349S169000, C349S177000, C349S033000
Reexamination Certificate
active
06268839
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 drive schemes for cholesteric liquid crystal displays that provide gray scale appearance. Specifically, the present invention is directed to drive schemes that utilize a range of voltages to drive a portion of the liquid crystal material to a particular texture and attain the desired gray scale appearance.
BACKGROUND ART
Drive schemes for cholesteric materials are discussed in U.S. patent application Ser. No. 08/852,319, which is incorporated herein by reference. As discussed therein, a gray scale appearance for bistable cholesteric reflective displays is obtained by applying a voltage within a range of voltages during a selection phase, which is one of a series of phases for voltage application pulses, to obtain the desired gray scale appearance. In that disclosed drive scheme, it is only appreciated that the cholesteric material can be driven from a non-reflective focal conic texture to a reflective planar texture. Moreover, when the material is driven from a non-reflective state to a reflective state, no consideration is given to the initial state of the liquid crystal material. In other words, a wide range of voltages is applied to the material, no matter if the material was initially in the focal conic texture or in the twisted planar texture. Accordingly, a wide undefined range of voltage pulses is required to drive the liquid crystal material to obtain a gray scale appearance.
As discussed in U.S. patent application Ser. No. 08/852,319, time modulation of the selection phase voltage may be employed to control the level of gray scale reflectance of the liquid crystal material. However, it has been determined that this method of voltage application may not be suitable for some cholesteric liquid crystal materials.
Based upon the foregoing, it is evident that there is a need in the art for drive schemes which more precisely drive cholesteric liquid crystal material to an appropriate gray scale appearance. Moreover, there is a need in the art to employ a drive scheme which allows for use of inexpensive driving circuitry. There is also a need in the art to provide a time modulation and amplitude modulation voltage application sequence that is adaptable to all cholesteric materials.
DISCLOSURE OF INVENTION
In light of the foregoing, it is a first aspect of the present invention to provide drive schemes of gray scale bistable cholesteric reflective displays.
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 and the other substrate 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 plurality of drive schemes, which are a single series of voltage pulses, that are used to drive a liquid crystal material between a non-reflective focal conic texture and a reflecting planar texture with various levels of reflectance therebetween depending upon the voltage values applied to the row and column electrodes.
A further aspect of the present invention, as set forth above, is to provide a drive scheme in which the liquid crystal material is initially driven to a reflective planar texture and wherein a predetermined range of voltages drives the liquid crystal material from the planar texture to the focal conic texture to exhibit gray scale reflectance properties.
Yet a further aspect of the present invention, as set forth above, is to provide a drive scheme in which all of the liquid crystal material is initially driven to a non-reflective focal conic texture and wherein a predetermined range of voltages drives the liquid crystal material from the focal conic texture to the planar texture to exhibit gray scale reflectance properties.
Yet an additional aspect of the present invention, as set forth above, is to provide a drive scheme in which all of the liquid crystal material is initially driven to a reflective planar texture and wherein a predetermined range of voltages drives the liquid crystal material from the planar texture to a focal conic texture to exhibit the desired incremental gray scale reflectance properties.
Still another aspect of the present invention, as set forth above, is to employ a time modulation technique to the applied voltage pulses to drive the cholesteric liquid crystal material to the desired gray scale reflectance.
Still another aspect of the present invention, as set forth above, is to employ an amplitude modulation drive technique to drive the cholesteric liquid crystal material to the desired gray scale reflectance.
The foregoing and other aspects of the present invention which shall become apparent as the detailed description proceeds are achieved by a method of addressing a bistable liquid crystal material having incremental reflectance properties disposed between opposed substrates, wherein one substrate has a first plurality of electrodes disposed in a first direction facing the other substrate which has a second plurality of electrodes disposed in a direction orthogonal to the first direction, the intersections thereof forming a plurality of pixels, the method comprising the steps of energizing the first and second plurality of electrodes to drive all the liquid crystal material to one of the first plurality of electrodes to a gray voltage value which is between first and second characteristic voltage values and the second plurality of electrodes to a second voltage value, wherein the second voltage value is between the difference between the gray voltage value and the first characteristic voltage value and the difference between the gray voltage value and the second characteristic voltage value, and wherein the difference between the first and the second voltage values generates a pixel voltage value, wherein if the pixel voltage value is between the first characteristic voltage value associated with minimum reflectance, the liquid crystal material between the first and second plurality of electrodes exhibits an incremental reflectance between the minimum and maximum reflectance.
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Yu and Kwok,A New Driving Scheme for Reflective Bistable Cholesteric LCDs, SID 97 Digest (1997), pp. 659-662.
Huang, Miller, and Doane,Unipolar Implementation for the Dynamic Drive Scheme of Bistable Reflective Cholesteric Displays, SID 97
Huang Xiao-Yang
Miller Nick M.
Yang Deng-Ke
Kent State University
Nguyen Jimmy H.
Renner Kenner Greive Bobak Taylor & Weber
Shalwala Bipin
LandOfFree
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