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Reducing Maximum Driving Voltage of Normally White-Mode Liquid Crystal Display Using Voltage-Controllable Compensation Liquid Crystal Cell

IP.com Disclosure Number: IPCOM000118709D
Original Publication Date: 1997-May-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 6 page(s) / 129K

Publishing Venue

IBM

Related People

Lien, S-CA: AUTHOR

Abstract

In (*), a thin birefringent layer is applied to a normally white Liquid Crystal Display (LCD) to reduce its maximum operating voltage. In this disclosure, a voltage controllable Liquid Crystal (LC) cell, which can easily be made, is used to replace the birefringent film. The simulation result shows it works as well as a thin birefringent film.

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Reducing Maximum Driving Voltage of Normally White-Mode Liquid Crystal
Display Using Voltage-Controllable Compensation Liquid Crystal Cell

      In (*), a thin birefringent layer is applied to a normally
white Liquid Crystal Display (LCD) to reduce its maximum operating
voltage.  In this disclosure, a voltage controllable Liquid Crystal
(LC) cell, which can easily be made, is used to replace the
birefringent film.  The simulation result shows it works as well as a
thin birefringent film.

      The configuration of a transmissive display system of
this disclosure is shown in Fig. 1.  It consists of a main cell, a
compensation cell and two polarizers.  (For the reflective type, a
polarizing beam splitter is used to replace two polarizers, similar
to that shown in Fig. 2.)  The main cell is a LCD cell which will be
operated in the normally white mode.  The compensation cell is a
voltage controllable LCD cell.  The main cell will display the image
and it can be Twisted Nematic (TN) cell, Super Twisted Nematic (STN)
cell, parallel Electrically Controllable Birefringent (ECB) cell,
homeotropically aligned nematic cell, Twisted Nematic-Electrically
Controllable Birefringent (TN-ECB) cell, or Hybrid Aligned Nematic
(HAN) cell, i.e., one substrate is homeotropically aligned and the
other substrate is homogeneously aligned.  The main cell can be a
transmissive panel or a reflective panel.  The compensation cell can
be parallel ECB cell, homeotropically aligned nematic cell, or HAN
cell.  The best angle between the projection of the alignment
direction of the compensation cell on the substrate plane and the
axis of the polarizer is 45 degrees, even though other angle can be
used.  The purpose of the compensation cell is to provide some small
amount of retardation (d Delta n) which is controllable by its
driving voltage to compensate out the residue birefringence of the
main cell when the main cell is driven under a high driving voltage.
The retardation of the compensation cell cannot be too large.
Otherwise, it will reduce the transmission of the whole system too
much when the main cell is driven under a low voltage.  The proper
amount of the compensation can be achieved by a proper design of the
cell gap and the  driving voltage of the compensation cell.

      To demonstrate how the invention works,...