FreeLists / si-list / [SI-LIST] Re: IBIS basic question

["Mike LaBonte" <milabont@xxxxxxxxx>]

Jing,

If the various IBIS I/V curves have currents in overlapping voltage ranges
those currents will be summed, at least in simulators that I am familiar
with. The proper technique of producing IBIS models, however, avoids having
the "same" current in more than one I/V curve. The output transistors are to
be disabled for clamp tests, and clamps are to be disabled for output tests.
Some techniques use subtraction if clamp disabling is not possible. Also,
the power and ground clamp curves are created over non-overlapping voltage
ranges.

Furthermore, best practice is to have the clamp curves fall to zero current
with a flat slope at the "inner" ends, so that when simulators guess the
"missing" data for each clamp curve (they have to make some assumption) they
will not extrapolate non-zero currents from the endpoints and sum those in.
The exception is for buffers with built-in termination, which in fact do
have non-zero current between 0V and VCC, but only in one clamp curve.

So the double counting you are asking about is a potential problem that is
to be avoided by careful model construction. For more info there is an IBIS
email list that is the best place to ask IBIS questions. Info below on this.

Mike LaBonte

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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Jing Wu
Sent: Wednesday, December 01, 2004 7:59 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] IBIS basic question

Hi, ibis experts:

    For  the GND clamp I-V curve, normally the data is taken from -Vcc to
Vcc while for the power clamp I-V curve, the data is taken from Vcc to 2Vcc.
How about if both the GND clamp and Power Clamp curve have the
data from    - Vcc to 2Vcc, will the simulator double-count the data or
different simulator have different solutions? =20

Thanks,
jing

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