RE: [SI-LIST] : Opamp spice model

Shenoy, Jay (Jay.Shenoy@VLSI.com)
Mon, 22 Mar 1999 15:28:26 -0800

Hi Raj,

If you are using HSpice, negative capacitances are handled correctly
in version 97.2
(verified myself) and above (caveat emptor). A couple of years ago, I was
correcting for
some over-counted capacitance from a particular extractor by using
subcircuits with negative
capacitance in it, and found this out the hard way. I think relatively
recent versions of Berkeley
Spice3 also do this correctly (ans so: all commercial derivatives of
Spice3). The reason: BSIM3v3
MOSFET model equations sometimes compute negative capacitances internally
and both
HSpice and Berkeley Spice had to account for this.

Problem with faking a negative capacitance with an Inductor divided by
square of omega
is in time domain simulations. For AC simulations, this should work fine....

Regards
Jay

> -----Original Message-----
> From: Rajkumar [SMTP:craj@india.ti.com]
> Sent: Saturday, March 20, 1999 10:09 AM
> To: si-list@silab.eng.sun.com
> Subject: [SI-LIST] : Opamp spice model
>
> Hi all,
>
> I am using some Opamps in a A/D test board. I wan to do
> some simulations on the reference circuit. I am taking the
> Opamp model from the Opamp manufactures. My problem is
> The spice model contains One Negative capacitor which denotes
> that there is a Zero in the Right Half Plane. But the simulation
> doesn't run with this Negative capacitance value. So, we have to
> comment out the line and run it which may not give right results.
> Is there any workaround for this problem.
>
> Looking forward for your mails.
>
>
> --
> Regards,
> Rajkumar.
> Texas Instruments India Ltd.,
>
>
>
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