Subject: Re: [IBIS] IV curve question...
From: Scott McMorrow (scott@teraspeed.com)
Date: Thu Oct 31 2002 - 11:32:20 PST
One possibility is that this could be due to a lack of DC convergence in
the initial operating condition.
I would go back and set up a transient simulation test case, where the
driver is attached to a test load to see if there are any issues with
the model. I would then sweep the resistive loading condition and
monitor the voltage and current, to see if you have the same behavior.
If under transient conditions the output is not stable over time, you
can simulate until it stabilizes and capture the nodal conditions.
These can be used as the initial DC conditions for the model extraction.
In any case, when extracting an IBIS model from spice, it is always
prudent to create your own test circuit to validate correct operation of
the spice model by itself.
best regards,
scott
-- Scott McMorrow Teraspeed Consulting Group LLC 2926 SE Yamhill St. Portland, OR 97214 (503) 239-5536 http://www.teraspeed.comIngraham, Andrew wrote:
>It does look similar to the effect you get when subtracting >clamp current from the total current. > >Except that it's in the wrong quadrant! > >These voltages should be in the normal operating region, >where the clamps shouldn't be doing anything. > >I think I've seen this before on some device (when extracting >I-V curves for our in-house turbo simulator). I don't know why or >how the device did that. It's been a long time so my memory is >hazy, but in that case I think it was a curiosity but not a >problem. In Matt's case either the curves, or something >else in the IBIS model, is a problem. > >I'd be curious what they thought they fixed when they made >you a new model. > >What sort of discontinuities do you see on the edges? Do >you mean that it suddenly changes voltage extremely fast? >Do you suppose the simulator sees two or more points of >convergence between the I-V curves and the load, and is >toggling between them? > >Does the model have V-T curves? > >Regards, >Andy > > >----------------------------------------------------------------- >|For help or to subscribe/unsubscribe, email majordomo@eda.org >|with the appropriate command message(s) in the body: >| >| help >| subscribe ibis <optional e-mail address, if different> >| subscribe ibis-users <optional e-mail address, if different> >| unsubscribe ibis <optional e-mail address, if different> >| unsubscribe ibis-users <optional e-mail address, if different> >| >|or email a request to ibis-request@eda.org. >| >|IBIS reflector archives exist under: >| >| http://www.eda.org/pub/ibis/email_archive/ Recent >| http://www.eda.org/pub/ibis/users_archive/ Recent >| http://www.eda.org/pub/ibis/email/ E-mail since 1993 > > > >
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