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From: tonjon@fluke.UUCP (Tony Johnson)
Newsgroups: net.analog
Subject: Re: The difference between capacitors and batteries
Message-ID: <133@vax2.fluke.UUCP>
Date: Tue, 11-Dec-84 14:30:41 EST
Article-I.D.: vax2.133
Posted: Tue Dec 11 14:30:41 1984
Date-Received: Fri, 14-Dec-84 06:01:43 EST
References: <158@decwrl.UUCP>
Organization: John Fluke Mfg. Co., Inc., Everett, WA
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> 
> 	A battery is an extremely nonlinear capacitor. This is due to
> the fact that the charge changes the characteristics of the dielectric.
> Period. They optimize difference aspects of similar phenomenon. You will
> find that all capacitors are somewhat nonlinear. Vendors tend to stuff
> this characteristic into the absolute tolerance. Polystyrene and 
> polypropalene ( spelling? ) tend to be the most linear. Batteries are
> the most nonlinear. You don't find many that are inbetween until you
> get to solid state capacitors processed in silicon, where the depletion
> layer varies with charge. The development of linear capacitors in IC's
> was a major breakthrough for systolic arrays and switched capacitor
> networks. It should be noted the the nonlinearity in silicon is inverse
> to the nonlinearity you find in batteries.
> 
> 					----{ john williams }----

	I have a question as to what we're talking about when we say 'non-
linear'...nonlinear as a function to what; frequency, applied voltage, time?
Polystyrene and 'polypros' have great performance with respect to a phenonmenon
called dielectric absortion i.e., they don't 'soak' as much as say mylar or
(yeech) electrolytic.  That's why they're great for use in integrating A/D 
converters.  But if one is concerned about nonlinear performance with respect
frequency i.e. 'hook', NPO ceramics perform very well.  A few references:

	Horowitz, Paul and Hill, Winfield; 'The Art of Electronics'; pg 18-19;
	Cambridge University Press; Cambridge, 1980.

	Pease, Robert A.; 'Understand capacitor soakage to optimize analog
	systems'; EDN, 13 October, 1982.

	Johnson, F.L.; 'Technical Bullitens 1-10'; Electrocube Corp.. You can
	probably get this stuff from the local Electrocube rep.

					Tony Johnson
					John Fluke Mfg. Co. Inc.
					Everett, WA