Subject: RE: [IBIS] IV curve question...
From: Silva, Benjamin P (benjamin.p.silva@intel.com)
Date: Thu Oct 31 2002 - 09:49:29 PST
That looks like a function of the way that the clamp curves were subtracted to create the IBIS file. If you added all the IV curves together (pulldown + VCC_clamp + GND_clamp), I would guess that you would not see non-monotonicities. The behavior you show in the waveform below is acceptable as long as no non-mon points are in the summation of the 3 IV curves.
Ben
> -----Original Message-----
> From: ruston, matt [mailto:ruston_matt@emc.com]
> Sent: Thursday, October 31, 2002 8:23 AM
> To: ibis@eda.org
> Subject: [IBIS] IV curve question...
>
>
> All:
>
> Hi. We have a vendor who has supplied us with IBIS models
> for one of their
> circuits. I was not too happy with the shape of the pullup
> and pulldown
> curves. The model also produced huge discontinuities on the
> switching edges
> while running the model in Hspice.
>
> The vendor made a new model for us, but when I look at the
> shape of the IV
> curves, they have the same shape as before:
>
>
> I (ma)|
> |
> |
> 20 |
> | ^--------------
> | / \
> 15 | / \
> | / \
> | / \____
> 10 | / \_______
> | /
> | /
> 5 | /
> | /
> | /
> |/
>
> ------------------------------------------------------------V
> /| 0.5 1.0 1.5 2.0 2.5 3.0
> / |
>
> Has anyone else ever seen any IV curves like these in an
> IBIS model? Why
> would they keep generating the same types of curves. I've never seen a
> pullup or pulldown transistor that behaves this way. The only
> possible thing
> that I can think of is some type of feedback circuit into the
> gate of the
> output transistors (some type of thermal protection or
> something). Or maybe
> these are measured curves and the heat generated during measurement is
> killing the "gain" at the higher currents and voltages? They
> do supply a
> min, typ, and max curve though.
>
> Any thoughts?
>
> Regards,
>
> Matt
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