RE: [IBIS] BIRD95.3: Power Integrity Analysis using IBIS

I find this paragraph of BIRD95.3 worthy of discussion:

|               These keywords might not have any effect for the Model_type
|               settings of Input, Input_diff, Terminator, Series, and
|               Series_switch.  These settings do not have a driver mode of
|               operation.

The analysis that lead to it is given:

6) Z_VDDDQ subparams and placement under Model_type - Bob Ross/John Angulo
 Added statement that the new keywords might not be used for Input,
Terminator,
 Series, Series Switch, Input_diff model_type.  The positioning of
[Composite
 Current] under the [Rising Waveform] and [Falling Waveform] keywords
already
 constrain that it is used only where the waveform tables are used.

This implies that the RLC+G circuit connecting the power and ground rails
inside the black box might not be present in an input model. I don't see
why. That predriver and bypass circuitry exists in inputs, and will cause
power and ground currents when the power-to-ground voltage changes due to
external influence, even in an input. Is the simulator expected to
selectively ignore the elements based on whether or not an IO or 3-state
buffer is enabled?

My opinion is that the IBIS specification should not use the word "might" in
any place that "might" cause 2 simulators to behave differently. The
elements should be absolutely present for almost any model type if they are
specified. The only exceptions would be the Series types, which do not have
power and ground connections; all BIRD95 keywords should be illegal for
those.

My apologies if I am jumping in late on something that has already been
discussed. I saw nothing about this change on the reflector.

While I'm at it I just have to mention the sinking feeling I get when I read
of new IBIS keywords that predefine structural elements that are simply R,
L, C, and G. It's just a shame that we are still going down that path and
not prescribing flexible circuit models, especially considering that
simulators will probably just apply the keyword values to a template in the
tool's own flexible macromodel-type language.

Mike LaBonte

-----Original Message-----
From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of Syed Huq
Sent: Tuesday, March 29, 2005 8:30 PM
To: ibis; ibis-users
Subject: [IBIS] BIRD95.3: Power Integrity Analysis using IBIS


Attached is BIRD95.3 with changes based on comments including those captured
at the March 11, 2005 IBIS Meeting.  The changes and justifications are
discussed in the ANALYSIS PATH/DATA section.

They include (1) changing the subparameters in BIRD95.2 to keywords for the
effective impedance per buffer, (2) not supporting *_ECL models at this
time, and (3) adding detail to the text based on some of the questions
raised.

BIRD95.3 will be discussed at the April 1st, 2005 IBIS Open Forum
teleconference.

Syed Huq
Cisco Systems, Inc
Acting Chair, EIA IBIS Open Forum

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