Subject: RE: [IBIS] IV curve question...
From: Tom Dagostino (tom@teraspeed.com)
Date: Thu Oct 31 2002 - 09:36:22 PST
I've seen curves like this in parts we modeled in the past but not many
recently. I have also been told by some IC vendors that in many buffer
designs there are intentional non-monotonic behaviors but I cannot tell you
if this is one of those. At 20 mA of current and 1.5V (30 mWatts) I doubt
that there is enough heat to cause this fold back in current.
Have you asked your vendor directly about this or tried to validate the
model with some measurements yourself?
Tom Dagostino
Device Modeling Division
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 430-1065
tom@teraspeed.com
http://www.teraspeed.com
-----Original Message-----
From: owner-ibis@server.eda.org [mailto:owner-ibis@server.eda.org]On
Behalf Of ruston, matt
Sent: Thursday, October 31, 2002 7:23 AM
To: ibis@server.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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