Re: [SI-LIST] : Ibis models

Laurence Michaels (lmichael@techmail.gdc.com)
Tue, 28 Sep 1999 10:46:42 -0400

Abe Riazi wrote:
>
> Jim Freeman Wrote:
>
> >> These ibis models as so generated are taken by both the
> >>ibis2xtk utility and the ibis2signoise utility and generate acceptable
> >>models to both of these simulators. In the Cadence info for the 2.1 GUI
> >>that they provide, it is stated that most simulators perform smoothing
> >>functions on the IBIS models before they use them.
> >
> >
> Hi Jim:
>
> Based on experience with IBIS and XTK models, I agree with above
> statements. The I-V sections of an IBIS model include:
>
> pullup
> pulldown
> GND_clamp
> POWER_ clamp
>
> The corresponding I-V curves of XTK models consist of:
>
> HIGH
> LOW
> SHUNT
> SHUNTP
>
> The IBIS format does not require monotonicity for the I-V tables.
> However, the XTK simulator demands that the I-V curves of the Quad
> models to be monotonic. When translating an IBIS model having
> non-monotonic I-V data, IBIS2XTK shifts the currents between the LOW/
> HIGH state curves and SHUNT/ SHUNTP curves (or deletes some points if
> necessary) towards generating monotonic curves.
>
> While I have seen numerous IBIS models having non-monotonic I-V data,
> I have not noticed any XTK models with non-monotonic I-V curves.

Abe, are you sure of the XTK monotonicity requirement? I seem to recall
that the earlier versions of XTK required monotonicity almost
everywhere,
but the newer ones relaxed many of those requirements. Quad stopped
supplying hard-copy manuals with new versions of software sometime last
year, so any official Quad manuals you might have are probably obsolete.
The online docs are still being updated with each release.

Anybody from Quad/Viewlogic High Speed Design care to comment?

Possibly useful SI information: Fasthenry from MIT seems to be very
nice,
and much cheaper (free?) than many commercial 3D inductance calculators.
I'm still checking it out myself, and it seems fairly stable so far.

Regards,

-- 
Laurence Michaels

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