Path: utzoo!utgpu!attcan!uunet!pyrdc!gmu90x!dana
From: dana@gmu90x.UUCP (J Dana Eckart)
Newsgroups: sci.electronics
Subject: Question about LCDs
Message-ID: <1240@gmu90x.UUCP>
Date: 29 Jul 88 20:52:25 GMT
Organization: George Mason University
Lines: 69


I have long been interested in liquid crystal displays (LCDs).  However, 
"acceptable" displays have only recently (in the past 2 years?) become 
available.  The three major difficulties, as I understand it, are:

	1) the slow response which makes for a slow refresh 
	   (although they have gotten much faster),

	2) individual pixels must be have a relatively large 
	   separation distance to prevent activating adjoining
	   pixels, and

	3) the more pixels per panel, the greater the likelyhood
	   that one will be bad (thus compromising the entire panel).

It occurs to me that all three of these problems can be circumvented by
layering several (4) panels.  Consider the following panel section, where
different numbers correspond to different panels.  [Gosh!  An application
of four coloring. :-)]

	   		3 4 3 1 3 4 3 1 3
	   		2 1 2 4 2 1 2 4 2
	   		3 4 3 1 3 4 3 1 3
	   		2 1 2 4 2 1 2 4 2
	   		3 4 3 1 3 4 3 1 3

The benefits of such a layout are:

	1) pixels on individual panels are separated by greater
	   distances than if fewer panels were used (to get the
	   same pixel density),

	2) the entire display can be refreshed in 4 parallel sections
	   (although whether or not this could truly be done in 
	   parallel depends upon the controlling hardware), and

	3) each panel, having fewer pixels, should be more reliable
	   to produce.

The use of multiple layers is possible because the principle behind an
LCD is that light be transmitted through nonoccluded pixels.  In fact, 
I think that multiple layers is the technique used for developing color 
LCDs.

The basic idea is to achieve a more pleasing display (with all the benefits 
of low power consumption, works well in bright light, small and flat, etc.) 
without requiring fundamental breakthroughs in technology.  Using multiple 
layers of LCDs seems to accomplish this.  In fact, this technique allows you 
to construct a display that has NO BLANK SPACE between pixels!

In fact, some quick calculations give a bit more information.  Suppose 
that we wanted a 12" square display with 1024 x 1024 pixels.  Then in order 
to have no blank spaces between pixels, each pixel must be about .012" square. 
This also means that the nearest pixel is also .012" away.  Do these figures 
fall into realm of possibility?  If not, what's the highest resolution one
could hope for with this method given current technology?  The above numbers
give about 85 pixels/inch.  How many pixels/inch could using layered panels
give (using current technology)?

I feel certain that I must be overlooking something rather obvious, otherwise
wouldn't this have already been done?  I am curious about what it is that I 
must have overlooked.  I welcome any comments.

Curiosity continues to kill the cat ...

J Dana Eckart
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