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From: norm@rocksanne.UUCP
Newsgroups: net.micro.68k
Subject: Re: Speedy 68020
Message-ID: <11800001@rocksanne.UUCP>
Date: Fri, 1-Nov-85 08:56:00 EST
Article-I.D.: rocksann.11800001
Posted: Fri Nov  1 08:56:00 1985
Date-Received: Sun, 3-Nov-85 04:49:43 EST
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Nf-ID: #R:l5:-22600:rocksanne:11800001:000:1915
Nf-From: rocksanne!norm    Nov  1 08:56:00 1985


> full temperature and voltage range.  But if the rumor is true, it does
> indicate that the chip is limited by power or temperature or
> fabrication tolerances (mechanical design), rather than by switching
> speed or electronic design.

	I am not clear on what you are saying here, the speed of the chips is
	really limited by switching speed.  Improvements in the fab lines
	or finer geometries will help improve the switching speed by
	either reducing loads or improving drive currents.  
	
	The temperature issue is something common to all silicon MOS devices.
	In a simple sense, the speed is limited by how fast you can 
	drive rc loads.  The drain current for a MOS device has a term
	in it that decreases as temperature increases.  Some of the
	data I have seen from MOS devices that we have done, and SPICE
	simulations indicate that for a rise from 27C to 50C the
	speed of MOS devices will decrease about 10%.  Cooling the devices
	will increase the drain current and hence the switching speed.
	
	There is actually a company (a CDC or Cray spin off ?) that is
	planning to market a "supercomputer" that uses CMOS gate arrays
	to build a processor and runs the devices at 70K.  They claim a
	2x-3x speed improvement over room temp (this info is a little
	sketchy in my memory but most of the data should be close).
	Given that the 020 runs at some where between 16-20Mhz then
	32-60 Mhz chips are possible with this technique.  However, the
	implementation details of such a system interconnect etc
	are not trivial.  Also the temperature decrease that helps
	in MOS devices makes bipolar devices run slower, so the
	interface circuits, if bipolar would not want to be cooled.



--------------
Norm Zeck
Xerox Corp.
800 Phillips Rd. 128-29E
Webster N. Y., 14580
ARPA:		NZeck.Wbst@Xerox.arpa
UUCP:		{decvax, allegra, seismo, cmcl2}!rochester!rocksanne!norm
Phone:		[USA] (716) 422 6246 
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