Subject: RE: ibischk3 V3.2.8 [Warning]
From: Matthew Flora (mflora@innoveda.com)
Date: Fri Feb 01 2002 - 08:00:53 PST
Dear T.Ura,
The warning is meant to alert you that the data in your clamp table
indicates
that the clamp never turns off, regardless of voltage.
I know that you're probably thinking that if the data in the table is
extrapolated, then the current will stop flowing at some voltage outside of
the table. That is a problem, because the simulator is forced to guess the
behavior of the device outside of the boundaries of the table. The
simulator might use linear extrapolation, cubic-spline extrapolation,
quadratic, etc. In fact, the simulator may not extrapolate at all and may
use the first and last currents in the table for all voltages beyond the
table (since extrapolation can result in ridiculous currents like 1e+26A).
The I-V tables are supposed to include data for all of the "interesting"
voltages of the buffer. The voltage at which current stops flowing is
certainly "interesting" and should be included in the table.
Since there may exist some technology for which current never stops or to
allow for measurement/calculation inaccuracies, IBISCHK3 will not report a
warning if the current get very close to zero. Very close was arbitrarily
chosen to be within 1uA. It seemed reasonable.
Best regards,
Matthew Flora
> -----Original Message-----
> From: Takanobu Ura [mailto:t-ura@pb.jp.nec.com]
> Sent: Friday, February 01, 2002 2:43 AM
> To: ibischk-bug@eda.org
> Cc: akimoto@lsi.nec.co.jp; t-ura@pb.jp.nec.com
> Subject: ibischk3 V3.2.8 [Warning]
>
>
>
> Dear all:
>
> I have checked our model with ibisckk3.
>
> As for model of xxx,The following WARNING is reported.
>
> WARNING -
> Model xxx: POWER Clamp : Typical value never becomes zero
>
> [Power Clamp] <- model of xxx
> 0 4.957u 5.049u 4.825u
> -76m 5.07u 5.376u 4.918u
> -152m 5.348u 6.904u 5.053u
> -227m 7.611u 15.19u 6.135u
>
> But,As for model of yyy, The above WARNING is not reported.
>
> [Power Clamp] <- model of yyy
> 0 0.557u 0.949u 0.225u
> -76m 0.567u 0.976u 0.229u
> -152m 0.548u 0.984u 0.253u
> -227m 0.611u 1.190u 0.335u
>
> What is the reason of this difference?
> Therefore,I have any question.
> a/ How did you decide the limitation value as like 1uA?
> b/ I cannot understand what this WARNING warns to us.
> Can I ignore this WARNING?
> Because,I think that clamp current is not surely zero.
>
> Regards,
> T.Ura
>
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