RE: help with ibischk3 warnings and min data

Hi,

Thanks for the clarification. I'm using s2ibis2 to create my IBIS model.
Does anyone have any suggestions on how I can correct these warnings?

Thanks,
Betty

> -----Original Message-----
> From: Tom Dagostino [mailto:tom_dagostino@mentorg.com]
> Sent: Tuesday, November 21, 2000 1:15 PM
> To: 'Betty Luk'; 'Kim Helliwell'
> Cc: ibis-users@eda.org
> Subject: RE: help with ibischk3 warnings and min data
>
>
> The IBIS parser tries to check for consistency between the DC
> and the AC
> parts of the model. The endpoint message says the steady
> state part of the
> AC waveforms does not match the predicted DC characteristics.
> If you were
> to take the part and put the output in a high state and
> connect a 50 Ohm
> resistor to ground the voltage on the resistor is predicted
> from the pull up
> curve. To calculate this voltage the parser places a load line on the
> curve, 50 Ohms to ground, and calculates the intersection of
> the pull up
> curve and the load line. Likewise for the pull down a 50 Ohm
> to Vcc load
> line is placed on the pull down and the intersection of the two is the
> predicted output low. If the predicted values do not match
> the end points
> in the model's AC tables within 2% the error is given.
>
> Tom Dagostino
> IBIS and Tau Modeling Manager
> SDD
> Mentor Graphics Corp.
> 503-685-1613
> tom_dagostino@mentor.com
>
>
> -----Original Message-----
> From: Betty Luk [mailto:Betty@genesis-microchip.com]
> Sent: Tuesday, November 21, 2000 10:05 AM
> To: 'Kim Helliwell'
> Cc: 'ibis-users@eda.org'
> Subject: 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 11:59:09 2000