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Half-Tone Methods for Passive-Matrix-Addressed Displays: LCD And ACTFEL

IP.com Disclosure Number: IPCOM000119374D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 3 page(s) / 157K

Publishing Venue

IBM

Related People

Pleshko, P: AUTHOR

Abstract

The implementation of the basic 16 gray shades on monochrome flat panels in which the amplitude of the excitation is used to modulate the visual output (contrast ratio or luminance) as, for example, in super-twisted-nematic liquid-crystal displays (STN/LCDs) or AC thin-film electroluminescent (ACTFEL) displays, puts high demands on the circuit impedances and tolerances and on the uniformity of the voltage-visual output characteristic of the display.

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Half-Tone Methods for Passive-Matrix-Addressed Displays: LCD And
ACTFEL

      The implementation of the basic 16 gray shades on
monochrome flat panels in which the amplitude of the excitation is
used to modulate the visual output (contrast ratio or luminance) as,
for example, in super-twisted-nematic liquid-crystal displays
(STN/LCDs) or AC thin-film electroluminescent (ACTFEL) displays, puts
high demands on the circuit impedances and tolerances and on the
uniformity of the voltage-visual output characteristic of the
display.

      The introduction of good visual quality, 16 grey scale STN/LCDs
has been thus inhibited due to STN display panel tolerances and due
to the well-known behavior of STN devices in which, when the contrast
is reduced by reducing the rms-drive voltage, the viewing angle also
reduces in a super-linear fashion.

      The introduction of 16 grey scale ACTFEL displays has also been
inhibited by the availability of low impedance gray scale driving
circuits and by the uniformity of the luminance-voltage
characteristic.  In addition, the effectiveness of the energy
recovery of the ACTFEL has also been negatively impacted due to the
nature of the amplitude-modulation driver circuits.

      Two such half-tone schemes are presented which do not require
capacitive balancing or anything more than a variation of the
geometries of the X and Y address lines. In the implementations shown
in Figs. 1 and 2, the sub-pixel areas are weighted 1-2-4-8,...