Re: [SI-LIST] : Opamp spice model

J. Eric Bracken (bracken@ansoft.com)
Mon, 22 Mar 1999 14:11:33 -0500

Rajkumar,

You can build a negative impedance converter easily enough in Spice:

X
A 0----+ +-----0-----+
| F1 = I(E1) | |
/ \ / \ |
/ | \ / + \ ----- |C| = -C
\ V / \ - / -----
\ / E1 = \ / |
| VA - VB | |
B 0----+ +-----0-----+
Y

.subckt negcap A B
F1 A B E1 1.0
E1 X Y A B 1.0
C1 X Y <positive-value>
.ends negcap

If your Spice doesn't allow the current in E sources to control
other sources, then you need to insert a zero-valued V source in
series with the E source to measure the current.

--Eric

>>>>> "Rajkumar" == Rajkumar <craj@india.ti.com> writes:

Rajkumar> Hi all,

Rajkumar> I am using some Opamps in a A/D test board. I wan to do
Rajkumar> some simulations on the reference circuit. I am taking
Rajkumar> the Opamp model from the Opamp manufactures. My problem
Rajkumar> is The spice model contains One Negative capacitor which
Rajkumar> denotes that there is a Zero in the Right Half
Rajkumar> Plane. But the simulation doesn't run with this Negative
Rajkumar> capacitance value. So, we have to comment out the line
Rajkumar> and run it which may not give right results. Is there
Rajkumar> any workaround for this problem.

Rajkumar> Looking forward for your mails.

--
J. Eric Bracken, Ph.D.                          Tel: 1.412.261.3200 x135
Group Leader, Signal Integrity R&D              Fax: 1.412.471.9427
Ansoft Corp., Four Station Square, Suite 200    bracken@ansoft.com
Pittsburgh, PA USA 15219-1119                   http://www.ansoft.com   

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