Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-04-21
2001-07-31
Chow, Dennis-Doon (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S095000, C345S210000
Reexamination Certificate
active
06268840
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a visual display utilizing a chiral nematic, also called cholesteric bistable liquid crystal material and an electronic drive system for activating the visual display using a pipelining scheme and unipolar waveforms to provide high-speed updating of the visual display.
BACKGROUND ART
Liquid crystals have been used to display information in flat-panel displays for many years, such as are commonly used in watch faces or half page size displays for lap-top computers and the like.
Liquid crystal displays made up of bistable chiral nematic materials do not require continuous updating or refreshing. When data or information changes on the display, the electronics update the display. If, however, the display information does not change, the display can be written once and remain in its information-conveying configuration for extended periods without display processor intervention. The ability to remain in a stable state for an extended period has resulted in use of chiral nematic liquid crystal displays for signs that can be slowly updated over relatively long periods of time. Since the display information does not change, the fact that it may take longer to write the initial information to the display is not important.
A number of prior art patents disclose techniques for updating liquid crystal display information. So-called liquid crystal display drivers or electronic circuits are known in the prior art and utilize various techniques for updating a liquid crystal display. U.S. Pat. No. 5,251,048 which issued Oct. 5, 1993 to Doane et al. concerns a method and apparatus for electronic switching of a reflective color display system. This patent discloses use of a liquid crystal light-modulating material that is confined between substrates. Elongated conductive paths supported on opposite sides of the substrates activate picture elements at controlled locations to set up a display screen. The disclosure of the '048 patent to Doane et al. is incorporated herein by reference.
A paper entitled “Storage Type Liquid Crystal Matrix Display” to Tani et al. (SID 79 Digest, p. 114-115) proposes a liquid crystal display driver system whose operation takes into account transitions between various states of a chiral nematic liquid crystal material. The paper describes a storage type liquid crystal display having the advantages of long storage time which makes refreshing or updating of the information on the display unnecessary. However, the Tani et al. drive scheme is limited in its resolution and information density conveying ability. His drive waveform and technology are limited in the number of lines that can be addressed to roughly 100 lines, far less than the 1000 lines required for page size viewer applications. Also, his demonstrated writing times of greater than 8 milliseconds (ms.) per line are insufficient for commercially acceptable page size viewers. On a flat-panel display or the like, 100 lines of information in a liquid crystal display is not acceptable for conveying text and 8 ms. per line is far too slow for many applications.
In the invention disclosed in U.S. application Ser. No. 08/390,068, filed Feb. 17, 1995 and entitled “Dynamic Drive Method and Apparatus For a Bistable Liquid Crystal Display,” a method and display driver circuitry for speeding the rate of updating a 1,000 row cholesteric liquid crystal display was disclosed. Application Ser. No. 08/390,068 is incorporated herein in its entirety by reference. An updating time of approximately one second for a 1000 row cholesteric liquid crystal display was achieved. By simultaneously addressing multiple rows of the display with a pipelining scheme, the overall updating time for the display was kept at one second.
DISCLOSURE OF THE INVENTION
Prior art systems known to applicant use a bi-polar driver which requires high voltage which are implemented with relatively expensive electronic drive circuits. The present invention is directed to a unipolar drive scheme which is implemented with lower cost drive electronics.
An exemplary embodiment of the invention concerns a method of activating a bistable liquid crystal material disposed between a first set of electrodes and a second set of electrodes arranged on opposed sides of said liquid crystal material. Driver electronics is adapted to selectively apply an electric field through said liquid crystal material.
The driver electronics energizes the electrodes to establish a preparation voltage across said liquid crystal during a preparation stage. Thereafter the drive electronics energizes said electrodes to establish a selection voltage across said liquid crystal during a selection stage. During the selection state a display state for said liquid crystal is chosen. Thereafter the drive electronics energizes the electrodes to establish an evolution voltage across said liquid crystal during an evolution stage and the liquid crystal material subsequently exhibits its final display state in a holding stage.
During the multiple energization stages the drive electronics applies a first unipolar waveform to one electrode of the first set of electrodes and a second unipolar square waveform to one electrode to the second set of electrodes. The results of the application of signals to the electrodes produces a bipolar selection voltage waveform for choosing the final state of the liquid crystal material. Most preferably, the drive circuit is used to activate a whole array of electrodes which update the liquid crystal material between the array. One application of the invention is for use with a page viewer for viewing text on a hand held viewing screen. Other uses, objects, advantages and features of the invention will become understood from a review of the detailed description of the invention which is described in conjunction with the accompanying drawings.
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Chow Dennis-Doon
Kent Displays Incorporated
Watts, Hoffmann, Fisher & Heinke Co. L.P.A.
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