Subject: Re: [IBIS-Users] Question about warning message
From: Kim Helliwell (kimgh@apple.com)
Date: Mon Nov 18 2002 - 11:08:03 PST
This is one of those areas where YMMV applies, I guess,
but I would say that most commercial simulators that handle
IBIS models are fairly good about filtering out non monotonic
behavior. At least, I've never had it be a problem. And it's
not clear how one is to combine the curves to check for
nonmonotoncity of the summed curves. I suppose that
pullup + powerclamp + groundclamp and pulldown + powerclamp
+ groundclamp would work, but during a transition, it's my
understanding that things are more complicated than that.
On the issue of extreme currents, I guess it depends on how
extreme. 100A would not give me heartburn, but I get really
nervous when we are talking about 10^14 or 10^25 amps.
While I suppose most simulators will take even these values
in stride, it always suggests a poor SPICE model used to create
the IBIS tables, which suggests sloppiness on the part of the
model maker. And that makes me wonder what else he/she
was careless about.
Kim
On Monday, November 18, 2002, at 10:27 AM, Angulo, John wrote:
> The following is posted on behalf of Tom Dagostino at Teraspeed
> Consulting Group. Please send any private replies to
> tom@teraspeed.com only.
>
> ----------------------------------------------------------------
>
> I'll disagree on this. The extreme currents are likely OK but the
> non-monotonic warnings may cause the simulations to not converge
> properly or
> in some simulators cause the model not to load at all. If the sum of
> the IV
> curves do not have monotonic issues you are OK. If the sum of the
> curves do
> have monotonic issues I would investigate before I would say it is OK.
>
> Tom Dagostino
>
> Device Modeling Division
>
> Teraspeed Consulting Group LLC
>
> 2926 SE Yamhill St.
>
> Portland, OR 97214
>
> (503) 430-1065
>
> tom@teraspeed.com
>
> http://www.teraspeed.com
>
> -----Original Message-----
> From: owner-ibis-users@server.eda.org
> [mailto:owner-ibis-users@server.eda.org]On Behalf Of Abdulrahman A.
> Rafiq
> Sent: Friday, November 15, 2002 11:32 PM
> To: Eric Hsu; ibis-users@server.eda.org
> Subject: Re: [IBIS-Users] Question about warning message
>
>
> Eric,
>
> The warning message of "non-monotonic" is perfectly acceptable and
> can be
> ignored. As for the warning message of extrreme currents present, it
> also is
> acceptable. In fact if you open the .ibs file and comment our all the
> extreme +ve and -ve currents in the I-V tables and then rerun
> ibischks, this
> warning message will not show up.
>
> In short you needn't worry too much about these warnings.
>
> Hope this helps.
>
> Regards,
>
> Abdulrahman Rafiq
>
Kim Helliwell
Apple Computer
kimgh@apple.com
408 974 9936
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