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Subject: Re: charge amp spice sim

Date: 09/19/02 at 12:14 PM
Posted by: Alex
E-mail: apike@microsensors.com
Message Posted:

In Reply to: Re: charge amp spice sim posted by Russ Kincaid on 09/19/02 at 8:55 AM:

I'm using ELDO.

I've tried two different variable capacitors. First, in ELDO a capacitor value can be determined by an expression. In my case, I set up an expression that tracked a node voltage. This node voltage was driven by a sine voltage source. Second, I used a macro model of a variable capacitor that was provide with the tool (Mentor Graphics). Here's the SPICE code for that macro model.

.SUBCKT VCCAP 1 2 3 {C=1E-12} {K=1}
IIN 3 0 DC 0
GIN 0 4 3 0 1
VCON 4 0 DC 0
C 1 5 C
V 5 2 DC 0
F 1 2 POLY(2) V VCON 0 0 0 0 K
.ENDS VCCAP

I've simulated a RC circuit with this macro model variable capcitor, using a transient analysis. The results were expected - a modulated sine wave, where the modulation was determined by the frequency of the varible capacitor. But this thing did not work in the charge amp.

Alex


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