RE: [IBIS-Users] Re: hspice vs IBIS model correlation at different capacitive loads

But it could be a problem with the way the IBIS model was made.

Vinayak, have you tested your IBIS model in any other simulators?  I
once had a model that worked in Cadence tools, but oscillated with
HSPICE.  I had to add some extra data points in the VI data to stop the
oscillations.


Aubrey Sparkman 
Enterprise Engineering Signal Integrity Team
Dell, Inc. 
Aubrey_Sparkman@Dell.com 
(512) 723-3592

-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of Andrew Ingraham
Sent: Wednesday, January 04, 2006 11:31 AM
To: ibis-users@eda.org; ibis@eda.org
Subject: [IBIS-Users] Re: hspice vs IBIS model correlation at different
capacitive loads

> I think he is saying that the oscillations happen because of the 
> feedback in the buffer is trying to settle to a steady state 
> condition.
>
> If so, legacy IBIS can not model your buffer, since there are no 
> provisions for describing feedback.

Yes.

Although it depends on the feedback.

Linear negative feedback, such as used on op-amps to reduce output
impedance, should work OK, I think.  It's probably also possible that
some forms of feedback to reduce variations in drive strength (for
example), ought to be somewhat compatible with conventional IBIS.  But
things like positive feedback to give hysteresis, don't play well in
IBIS.

Regards,
Andy


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