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Driving Method for Thin Film Transistor Liquid Crystal Display with Contrast Control

IP.com Disclosure Number: IPCOM000114427D
Original Publication Date: 1994-Dec-01
Included in the Prior Art Database: 2005-Mar-28
Document File: 4 page(s) / 69K

Publishing Venue

IBM

Related People

Kimura, Y: AUTHOR [+3]

Abstract

Disclosed is a driving method for Thin Film Transistor Liquid Crystal Display (TFT LCD) which has a contrast control function. This method has the following advantages: 1. Power reduction for LCD drive circuit at minimum contrast setting. 2. Improvement for screen contrast at maximum contrast setting.

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Driving Method for Thin Film Transistor Liquid Crystal Display with
Contrast Control

      Disclosed is a driving method for Thin Film Transistor Liquid
Crystal Display (TFT LCD) which has a contrast control function.
This method has the following advantages:
  1.  Power reduction for LCD drive circuit at minimum contrast
       setting.
  2.  Improvement for screen contrast at maximum contrast setting.

      Fig. 1 shows a transmission versus drive voltage
characteristics of the twisted nematic type (normally white) TFT LCD.
The screen contrast is controlled by common voltage.  Each drive
voltage of the gray scales changes when operator controls the
contrast setting position.  Display pattern and drive voltages affect
the power consumption.  An all-black pattern (darkest gray scale) at
maximum contrast setting is the worst case for power consumption.
Voltages for gray scales A and B are shown in this Figure.  If the
operator sets the contrast at minimum (darkest position) the common
voltage goes to maximum in the conventional drive method.  For
example, gray scale (darkest gray scale) voltage A goes to A1 when
contrast set to minimum.  The voltage change does not affect the
transmittance, but power consumption will increase.  Because the
switching losses for drive circuit and electric charge for liquid
crystal cell increase at minimum contrast setting.  On the other
hand, gray scale voltage A goes to A2 when contrast set to maximum.
The voltage c...