Subject: Re: ibischk3 V3.2.8 [Warning]
From: Ingraham, Andrew (Andrew.Ingraham@compaq.com)
Date: Mon Feb 04 2002 - 12:54:57 PST
> The I-V tables are supposed to include data for all of the
> "interesting"
> voltages of the buffer.
I wish this were so.
I really do wish that IBIS had required ALL I-V tables to completely
cover all normal voltages of the buffer.
What is the current from the [POWER Clamp] table when the buffer voltage
is 0V? Or +1.0V, or -1.0V? It doesn't say. The [POWER Clamp] table
doesn't cover these voltages. It apparently assumes that the current
due to the POWER Clamp should be negligible there and doesn't need to be
tabulated.
But what if it isn't?
Or what if ... for whatever reason ... the values in the [POWER Clamp]
table do not asymptotically approach zero as the buffer voltage
approaches POWER?
There are no IBIS rules for extrapolation. Therefore, the results are
entirely unpredictable. Ugh!
As noted, one simulator might continue the last current value
indefinitely, another might extrapolate with a constant slope. Yet
another might assume ZERO current beyond the defined I-V tables, causing
a rather large discontinuity.
Sure, the IBIS spec claims that "this data must not be left for the
simulator to provide," but that is, unfortunately, a false statement.
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