Browse Prior Art Database

Automatic Contrast Control for LCD

IP.com Disclosure Number: IPCOM000101990D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 65K

Publishing Venue

IBM

Related People

Kimura, Y: AUTHOR [+2]

Abstract

Disclosed is an automatic contrast control circuit for LCD (Liquid Crystal Display). This circuit (method) is applicable to a simple matrix-type LCD, especially large-size, high-duty application.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 56% of the total text.

Automatic Contrast Control for LCD

       Disclosed is an automatic contrast control circuit for
LCD (Liquid Crystal Display).  This circuit (method) is applicable to
a simple matrix-type LCD, especially large-size, high-duty
application.

      In a simple matrix LCD, an optimized amplitude selective
addressing scheme is widely used to minimize crosstalk.  The scanning
voltage is applied to the selected common electrode, while bias
voltage are applied to the segment electrode.  The maximum voltage
ratio is the ratio between the maximum voltage applied to selected
pixels and the minimum voltage applied to the unselected pixels.  The
ratio becomes very small as the number of common electrodes is large.
As the number of the picture elements is increased, the effect of
capacitive and resistive crosstalk should be increased.  Variation of
liquid crystal cell parameter, such as cell thickness, also causes
variation of the threshold voltage.

      A display has two display modes.  One is dark character/image
on a light background mode and the other is light character/image on
a dark background mode.  In general, polarity change of display data
signal produces mode change.  Fig. 1 shows the transmission versus
voltage characteristics of the LCD.  (a) is the ideal
characteristics.  Actual threshold sharpness and variation of the
above characteristics are shown in (b).  In dark character on light
background, the operator changes the contrast volume as backgr...