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Liquid Crystal Display Utilizing Photosensor Feedback

IP.com Disclosure Number: IPCOM000121144D
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 77K

Publishing Venue

IBM

Related People

Goldowsky, M: AUTHOR

Abstract

Disclosed is a liquid crystal display incorporating a light intensity sensor at each pel. Many levels of gray scale can be obtained using closed loop control. A photosensor and Brewster angle polarizer at each pel comprise the intensity sensor that mimics the intensity seen by the viewer.

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Liquid Crystal Display Utilizing Photosensor Feedback

      Disclosed is a liquid crystal display incorporating a
light intensity sensor at each pel.  Many levels of gray scale can be
obtained using closed loop control.  A photosensor and Brewster angle
polarizer at each pel comprise the intensity sensor that mimics the
intensity seen by the viewer.

      Fig. 1 is a cross section through a nematic liquid crystal
display at the location of one pel.  The inside of the bottom glass
surface incorporates a doped silicon photocell.  For the photocell to
respond to the intensity changes that a viewer sees, the internal
light must be polarized, similarly as is the light that reaches one's
eye after the display's polarizer.  An internally polarized beam is
obtained by causing input aperture light to reflect off the top plate
at the Brewster's angle.  The reflected Brewster beam is 100%
perpendicularly polarized and is incident on the photocell.  As the
pel is turned on, the liquid crystal material rotates the plane of
polarization, and after passing the Brewster reflection, the
intensity on the photocell increases.  Operation of this sensor
portion was experimentally verified.

      The photocell's proportional signal is amplified and compared
to a reference.  The error is used to proportionately turn on the pel
until the desired intensity is obtained.  This simple feedback
circuit can be incorporated on the pel during fabrication of the Thin
Film Transistor...