RE: help with ibischk3 warnings and min data

Hi Kim,

For your point 2), I'm not sure what I should be comparing my VT data with
(ie. which part of the VI data). I think I'm still unclear on what the
warning message means.

Thanks,
Betty

> -----Original Message-----
> From: Kim Helliwell [mailto:khelliwe@acuson.com]
> Sent: Tuesday, November 21, 2000 12:38 PM
> To: Betty Luk
> Cc: 'ibis-users@eda.org'
> Subject: Re: help with ibischk3 warnings and min data
>
>
> > Betty Luk wrote:
> >
> > Hi,
> >
> > I appreciate all the help I have been getting so far.. thanks!
> >
> > I have built my IBIS model using s2ibis2, typ, min and max
> data. The data for my min curve seem to be a bit strange
> > (when I looked at the curves using s2iplt), and the IBIS
> golden parser is complaining about non-monotonic data. I am
> > not sure whether I should try to fix these warnings or not,
> because they are not just isolated occurences of
> > non-monotonic data (ie. I cannot just discard the
> problematic point). I have included my IBIS model for
> > convenience. These are the warnings that I get:
> >
> > WARNING (line 52) - Pulldown Minimum data is non-monotonic
> > WARNING (line 134) - Pullup Minimum data is non-monotonic
> > WARNING (line 307) - POWER Clamp Typical data is non-monotonic
> > WARNING (line 308) - POWER Clamp Minimum data is non-monotonic
> > I also get another warning. What does this warning mean?
> >
> > WARNING - Model 'tristate_driver': MIN AC Rising Endpoints
> ( 0.00V, 0.89V) not within
> > 0.018V (2%) of (-0.02V, 0.84V) on VI curves for
> 50 Ohms to 0V
> >
> > I would really appreciate any feedback!
> >
> > Thanks,
> > Betty Luk
> >
> >
> >
> >
> >
> >
> > Name: test.ibs
> > test.ibs Type: unspecified type (application/octet-stream)
> > Encoding: quoted-printable
>
> 1. I believe that most simulators currently available filter
> the IBIS table data
> so as to remove nonmonotonicity from the data. That's not
> to say it's not
> better to remove it yourself first. It might be a good
> idea to check the
> actual curves from the simulator you're using with s2ibis2
> and see whether
> the nonmon behavior is present in the data, or whether
> it's introduced by
> the interpolation routines in s2ibis2. If it is present
> in the actual
> simulation output, does the nonmonotoncity appear to be
> severe? If so, then
> perhaps there are problems with the models you are using.
> If it's minor,
> and if it's outside the normal supply range, it probably
> won't hurt things
> too much.
>
> I would say: do your best to eliminate this problem, but
> if it's not possible,
> you may have to rely on the filtering in your customer's
> simulators.
>
> 2. The problem with your AC warning is that the start and end
> values of the
> V-T curves do not match the start and end values of the VI
> curves. You need
> to understand why this is happening, which will involve
> looking at the SPICE
> netlists and output for the VI and VT curves. The lower
> endpoint is probably
> close enough to ignore, but the upper one is a bit further
> off. There is a
> risk that some simulators your customers use will not
> tolerate this too well
> and simply fail or (worse) quietly give the wrong answer.
>
> In any case, any warnings you don't fix should be mentioned
> in comments in the
> resulting IBIS file, so your users don't panic when they see
> the warnings.
>
>
> --
> Kim Helliwell
> Senior CAE Engineer
> Acuson Corporation
> Phone: 650 694 5030 FAX: 650 943 7260
>
 
Received on Tue Nov 21 10:04:54 2000