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From: jpm@calmasd.CALMA.UUCP (John McNally)
Newsgroups: comp.graphics
Subject: Re: CRT technology?
Message-ID: <2138@calmasd.CALMA.UUCP>
Date: Wed, 14-Jan-87 19:50:29 EST
Article-I.D.: calmasd.2138
Posted: Wed Jan 14 19:50:29 1987
Date-Received: Fri, 16-Jan-87 01:25:00 EST
References: <1219@ucbcad.berkeley.edu>
Organization: G.E. CALMA R&D, San Diego, CA
Lines: 53
Summary: LCD Displays - color, high resolution, and update speed

In article <1219@ucbcad.berkeley.edu>, faustus@ucbcad.berkeley.edu (Wayne A. Christopher) writes:
> Maybe somebody who knows a lot about CRT technology can answer a few
> questions I've been wondering about... 
> How about LCD displays?  Is
> there any theoretical reason for LCD's to be more or less suitable than
> CRT's for such high-resolution displays?  (Is it even possible to make
> multiple-color LCD's?)  Thanks in advance for the enlightenment,

Liquid Crystal Displays are just one of many forms of flat panel
displays - others include plasma and electroluminesence.  Each has
advantages and disadvantages.  For example, plasma screens are
capable of high resolution and fast update speeds but require high
voltage and are limited (currently) to an orange color.  LCD
displays have very low power requirements but (currently) have
poor contrast, viewing angles, and update speeds.  All flat panels
obviously have the advantage of reduced space and simpler
packaging than CRTs.  However, there are even prototypes of "flat"
CRTs (the electron gun is parallel to the tube and the deflection
subsystem is radically different).  The "winner" in this
competition is yet to be determined...

Currently LCDs appear to be the most promising flat panel
technology and I expect that ultimately they will capture a major
share of the display market.  However, there are significant
technical problems to be overcome (the Japanese are very active in
this area).  To me the most critical problem is the speed of
update.  Currently commercially available LCDs of any reasonable
size do not have "pixel addressing"  Writing to one pixel on a
line or all pixels on a line requires the same amount of time -
about 15 milliseconds.  There are a lot of related problems in
this area, but what it bolis down to is that LCDs are very slow in
updating.  Thin film transistor technology
will solve this problem, but the technology has not yet reached
the stage of mass manufacturing (several companies, mostly
japanese are close).

I refer you to an article that appeared in High Technology (May
1984, pp. 55 - 69), "LIQUID CRYSTALS  BIG, BRIGHT, EVEN COLORFUL
DISPLAYS".  This is a good survey article on LCD technology.  It
discusses thin film transistor for active matrix addressing, the
various methods used to make liquid crystals "turn on and off",
and how color is introduced (using organic dyes).  It also
discussed futures and applications, and the inherent problems I
have touched upon in much greater clarity.

I think that it is premature to consider the use of LCD displays
for CAD, especially areas requiring extremely good image quality
(like solids modeling).  We are still many years away from
providing a cheap, reliable alternative to the 1024 x 1024 color
CRT! (and the CRT manufacturers are not sitting still).
-- 
John McNally  GE/Calma  9805 Scranton Rd. San Diego CA 92121
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