RE: [IBIS] Composite current and Initial dead time in waveform table

Prabhat,

You are raising a very good point. The question is how much
can you remove from the beginning of the waveform tables.

You wrote that the "IBIS specification recommends to remove
the initial non-switching time". I tried to find this in
the specification to double check the exact wording, but I
can't find this recommendation in the specification. Can you
give me a page number for it? Or is this in the Cookbook?

Either way, common sense would dictate that if you want to
be able to get correct power currents, you should NOT chop
off the beginning of the I-T table just because the V-t table
is inactive. In other words, when you decide how much to shift
the waveforms to the left, don't make your decision solely based
on the content of the V-t tables, look at the I-T tables also
and move things to the left only by as much as the shortest
inactive I-T or V-t waveform lets you.

Please let me know where the spec or Cookbook talks about this
so we could make the necessary corrections if the wording is
incorrect or misleading. Please keep in mind that the I-T
tables were added much later to the specification as the V-t
tables, and we may have forgotten to update some text which
deals with this topic in the V-t sections when the I-T section
was added.

Arpad
================================================================

-----Original Message-----
From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of
Prabhat RANJAN
Sent: Wednesday, December 15, 2010 9:34 PM
To: ibis@eda.org; ibis-users@eda.org
Cc: Prabhat RANJAN
Subject: [IBIS] Composite current and Initial dead time in waveform
table

Hello Experts,

Composite current tables have been introduced in IBIS ver5.0 for better
modeling of pre-driver and driver current.
In buffers, major pre-driver current flows from source just after input
stimuli transition and before the output driver actually starts
switching.

Also, IBIS specification recommends to remove the initial non-switching
time (or dead-time or startup time) from waveform tables to avoid the
over-clocking issues.

If my buffer needs to remove the initial non-switching time from
waveform tables then I have to remove or shift the corresponding
composite current tables also. This shifting of composite current will
remove all pre-driver currents from tables and hence I shall not be able
to get advantages of composite current.

In most of high speed buffers, non-switching times should be removed
from waveform tables but we also need complete composite current with
pre-driver current for accurate power integrity.

So, I am wondering that how composite current tables are going to be
useful in above cases??

-- 
Regards
Prabhat Ranjan
STMicroelectronics
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