[IBIS] IV curve question...


Subject: [IBIS] IV curve question...
From: ruston, matt (ruston_matt@emc.com)
Date: Thu Oct 31 2002 - 07:23:15 PST


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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