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From: jones@fortune.UUCP
Newsgroups: net.micro
Subject: Re: 74S124 as xtal osc - (nf)
Message-ID: <3829@fortune.UUCP>
Date: Thu, 19-Jul-84 20:07:09 EDT
Article-I.D.: fortune.3829
Posted: Thu Jul 19 20:07:09 1984
Date-Received: Fri, 20-Jul-84 04:46:30 EDT
Sender: notes@fortune.UUCP
Organization: Fortune Systems, Redwood City, CA
Lines: 47

#R:utzoo:-402300:fortune:28000045:000:1934
fortune!jones    Jul 19 16:44:00 1984

About 5 years ago, when I was at Qantel Corp (before they became
MDS Qantel), we went through the engineering drill of deciding
whether to continue with gate/oscillator clock circuits.  We 
were pretty heavy into intelligent controllers and had Z80s
everywhere.  We came to the conclusion that it was better to
hand off the problem to somebody else and buy hybrid oscillators.
One would think that a manufacturer with control of all the
variables would be able to solve all our problems.  Well, they
did finally but in the early days we saw all the problems:
cracked substrates, poor solder seals, out of spec duty cycles,
temperature sensitivity, voltage sensitivity, and delayed
oscillation.  Hybrid oscillators are great, but it pays to
test them.

As for gate oscillators, the following is from Jim Williams article,
_Basic Circuit-design Techniques Yield Stable Clock Oscillators_,
in the August 18, 1983 edition of EDN:

	While gate oscillators are quite popular, they can
	cause problems ranging from tempermental operation
	to lack of oscillation.  The gain elements are the 
	primary problem source-it's not possible to reliably
	identify the analog characteristics of digital gates.
	For example, there's no guarantee that gates from
	various manufacturers will produce the same results
	when plugged into the oscillator circuit.  In other
	cases, the circuit will work but the status of the 
	other gates within the package will affect its
	performance.  Finally, some circuits seem to favor
	certain gate locations within the IC package.

	Given these difficulties, gate oscillators are not
	the best possible choice in a PRODUCTION DESIGN.
	They do deserve mention, however, because they can
	satisfy noncritical applications.

The emphasis is mine.

Dan Jones

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