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