Browse Prior Art Database

PRIVACY SWITCH FOR LIQUID CRYSTAL DISPLAYS

IP.com Disclosure Number: IPCOM000007706D
Original Publication Date: 1996-May-01
Included in the Prior Art Database: 2002-Apr-16
Document File: 2 page(s) / 92K

Publishing Venue

Motorola

Related People

Robert Atkins: AUTHOR

Abstract

There may be situations in which it is advanta- geous to have a display on a product such as a radio or pager, which does not display its information until the operator desires to see it and activates a switch. The following method is a very simple means of incorporating such a switch into a display.

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MO7VROLA Technical Developments

PRIVACY SWITCH FOR LIQUID CRYSTAL DISPLAYS

by Robert Atkins

  There may be situations in which it is advanta- geous to have a display on a product such as a radio or pager, which does not display its information until the operator desires to see it and activates a switch. The following method is a very simple means of incorporating such a switch into a display.

  Typically displays have at least two distinct opti- cal states, and may be switched via the application or removal of an electric field between the two states. One of these optical states is usually a stable state, to which the display relaxes in the absence of an applied field. The other state(s) are unstable, and obtained by application of the electric field. Exam- ples of such displays include those based on twisted nematic liquid crystals, super twisted nematic liquid crystals, polymer dispersed liquid crystals, etc. (but are not limited to liquid crystal based displays). Many types of displays, especially those mentioned above, respond to the root mean square (or RMS) voltage applied to them, and are therefore insensitive to the polarity ofthe applied field. At a certain applied field (referred to as the threshold field) these displays begin to respond to the applied held and switch to the other optical state. At a higher field, called the satu- ration held, the display is completely in the unsta- ble optical state. A characteristic width of the tran- sition can be defined as the difference between the saturation field and the threshold field. A simple privacy switch can be made for any display, provided that the width of the transition (defined above) is approximately less than or equal to % the satura-

tion field (this is equivalent to requiring that Vthreshold be greater than % V,...