RE: help with ibischk3 warnings and min data

Hi,

Actually, I noticed something strange about the warnings generated from the
IBIS golden parser. I've pasted all the warnings below:

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
WARNING - Model 'tristate_driver': MIN AC Rising Endpoints ( 1.84V, 3.00V)
not within
          0.023V (2%) of ( 1.83V, 2.85V) on VI curves for 50 Ohms to 3V
WARNING - Model 'tristate_driver': MIN AC Falling Endpoints ( 0.00V, 0.89V)
not within
          0.018V (2%) of (-0.02V, 0.84V) on VI curves for 50 Ohms to 0V
WARNING - Model 'tristate_driver': MIN AC Falling Endpoints ( 1.84V, 3.00V)
not within
          0.023V (2%) of ( 1.83V, 2.85V) on VI curves for 50 Ohms to 3V
WARNING - Model 'tristate_driver': MAX AC Rising Endpoints ( 0.00V, 1.89V)
not within
          0.038V (2%) of ( 0.00V, 1.98V) on VI curves for 50 Ohms to 0V
WARNING - Model 'tristate_driver': MAX AC Rising Endpoints ( 1.34V, 3.60V)
not within
          0.045V (2%) of ( 1.34V, 3.79V) on VI curves for 50 Ohms to 3.6V
WARNING - Model 'tristate_driver': MAX AC Falling Endpoints ( 0.00V, 1.89V)
not within
          0.038V (2%) of ( 0.00V, 1.98V) on VI curves for 50 Ohms to 0V
WARNING - Model 'tristate_driver': MAX AC Falling Endpoints ( 1.34V, 3.60V)
not within
          0.045V (2%) of ( 1.34V, 3.79V) on VI curves for 50 Ohms to 3.6V

For example, in the last warning statement, it states the correct range to
be ( 1.34V, 3.79V). If my supply voltage is 3.6V, how can the final
voltage be 3.79V, higher than 3.6V?

Thanks very much,
Betty

> -----Original Message-----
> From: Betty Luk [mailto:Betty@genesis-microchip.com]
> Sent: Tuesday, November 21, 2000 3:00 PM
> To: 'tom_dagostino@mentorg.com'; 'Kim Helliwell'
> Cc: ibis-users@eda.org
> Subject: 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 13:42:35 2000