Xref: utzoo sci.research:1536 sci.electronics:18020
Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!dali.cs.montana.edu!milton!whit
From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.research,sci.electronics
Subject: Re: Variable Capacitor in SPICE
Message-ID: <17096@milton.u.washington.edu>
Date: 25 Feb 91 05:01:02 GMT
References: <1991Feb21.223126.15937@sol.UVic.CA>
Distribution: na
Organization: University of Washington, Seattle
Lines: 25

In article <1991Feb21.223126.15937@sol.UVic.CA> shankar@face.UVic.CA (P.S.Shankar.) writes:

>   I am trying to simulate what is essentially a RC circuit using SPICE. 
>   ... I need to put in
>   capacitors, whose values depend on the voltages on them, all of which are 
>   typically time-varying.

	This is where the controlled sources come in handy.  First,
replace the capacitor by a current meter (zero V voltage source), and
a voltage-controlled voltage source in series.  Then make a
current-controlled current source onto a dummy capacitor, whose
output current is identically the current measured by the current
meter.
	So you now have a dummy capacitor whose state of charge
is identical to that of your real capacitor.  Its voltage, of
course, is proportional to the capacitor charge.  SO, now use
a voltage-controlled voltage source (controlled by the voltage on
the dummy capacitor) to emulate the REAL capacitor (of course, the
controlled source is exactly the one you replaced your capacitor with.

	The rest of the solution will involve translating the
behavior of your (voltage-variable capacitor diode?) into a 
suitable form (Vcapacitor= polynomial in Qcapacitor).

	John Whitmore


Brought to you by Super Global Mega Corp .com