RE: [SI-LIST] : Ibis models

Geoff Parker (geoff@viewlogic.com)
Tue, 28 Sep 1999 09:59:10 -0700

I just wanted to clarify a point in Abe's post. XTK can use
non-monotonic
curves under the restriction that the resulting _sum_ of the HIGH/LOW
curve with the shunts (SHUNTP & SHUNT) is monotonic. If an XTK curve
is non-monotonic, it should used the keyword NON_MON in the model.

Note the relationship between Ibis and XTK I-V curves.

Ibis XTK
------------------------ -----------------------
[Pullup] + [*_Clamp]'s = HIGH + (SHUNT + SHUNTP) (sum must be
monotonic)
[Pulldown] + [*_Clamp]'s = LOW + (SHUNT +SHUTNP (sum must be
monotonic)

It is common to find Ibis files with one or more non-monotonic I-V
curves.
Although the Ibis standard does not require monotonicity for the I-V
curves, the sum of the Ibis curves shown above should be mononotic for a
"well behaved" Ibis model (read correct). Chris Rokusek gave a good
explaination on why in a previous post.

The recent versions of the ibis2xkt translator do not modify the Ibis
curves to be non-monotonic unless absolutely necessary (e.g. the sum of
[Pullup] and [Power_Clamp] is non-monotonic, or interpolation requires
minor adjustments).

Best Regards,

#---------------------------------------------------------------
# Geoff Parker gparker@viewlogic.com
# Software Engineer
# Viewlogic Systems 1369 Del Norte Rd.
# Signal Integrity Group Camarillo, CA 93010

On Sat, 25 Sep 1999, 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.
>
> Regards,
>
> Abe
> ariazi@anigma.com
> >
> >
>
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