Subject: RE: [IBIS] BIRD 75 comments
From: Muranyi, Arpad (arpad.muranyi@intel.com)
Date: Wed Aug 28 2002 - 08:29:56 PDT
Lynne,
Thanks for your comments. Regarding your last question, I was
wondering about that too, i.e. how can we reference the new
interconnect specification from the IBIS model. There is a
new keyword in BIRD75, [External Circuit], which inserts a
passive circuit description, but strictly speaking it was
designed to place that circuit between the buffer model and
the die pad. Therefore it doesn't seem to be intended to
reference any external interconnect models as I understand it.
However, I also feel that we should have a way to utilize our
new ICM spec for modeling these more elaborate on-die interconnects
as well as packages.
Regarding the required subparameters and keywords, my point was
not whether to keep them or not, but that they are also becoming
too rigid the way we had them so far. What if I make an [External
Model] which needs a parameter for Vcommon in addition to Vdif,
plus edge rate values at which the input signal is valid for the
differential receiver? Or what if the [External Model] has more
supply connections than just the four for which we now have the
reference voltage keywords? We won't be able to do it until a
new BIRD is written and approved. My suggestion is to make a spec
that allows the model maker to define their own parameters, and
actions that the parameter needs to achieve in the simulator and
then have the simulator parse it, and solve it. This is similar
to stepping up from a basic calculator which has only four functions
to a math software where you can write your own equations and have
it solve it for you.
The other point I was trying to make is that the current spec
requires some of the parameters/keywords under the old [Model]
keyword. It seems to be silly (and confusing) to have to define
C_comp and [Ramp] with zeroes or NAs in a model when they are
described much better in the [External Model], just because
the spec required their presence.
Arpad
==============================================================
-----Original Message-----
From: Lynne Green [mailto:lgreen@cadence.com]
Sent: Tuesday, August 27, 2002 1:18 PM
To: ibis@eda.org
Subject: RE: [IBIS] BIRD 75 comments
Great discussion thread so far. Arpad and Bob have
addressed some major points in depth.
Several keywords/subparameters we may want to keep,
whichever way the BIRD decides to go:
receiver thresholds
Vmeas, Cref, Rref, Vref
Enable polarity
all of the various test fixtures, including golden waveforms
Model_type
voltage range (perhaps extend to Vss as well as Vcc).
temperature range
reference voltages, external reference
[Ramp], because algorithms can use this to estimate
the edge rate for various calculations.
The suggestion of setting C_comp to 0pF if it is included in
the external model leaves the model maker a choice of
where to include it. Choice is good, unless it is confusing
to the model maker.
The "philosophy" appears to offer two choices:
Put [External Model] under [Model], and list all the things that
must NOT be included, or separate the two and list all the things
that MUST and CAN be included. Any insight on which might
be easier for a parser implementation?
One new question: Can an [External Model] be used to replace
a package model? This might be a way to address typ/min/max
package variations in a complex package.
Best regards,
Lynne
Lynne Green
Senior Member of Consulting Staff
Cadence Design Systems, Inc.
"All the world's an analog stage, whereon digital plays bit parts."
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