Subject: BIRD #5

From: Bob Ward <[email-masked]>
Date: Thu, 9 Dec 1993 17:23:57 -0600

Hi ibis'ians!

I was just reading Randy's note about BIRD #5, and it sparks the following
comments.  First, I agree fully with Randy's observation that the bussing
structures are generally more complicated that what BIRD #5 allows for.  In
fact the power and ground tree structures I was harrangueing about earlier
are prime examples of this carried to something of an extreme.  Now in the
last forum we discussed this at some length, and concluded, I think :^), as
follows.  BIRD #5 should be slightly amended as we discussed it and then
basically accepted pending any further comment.  I would make a try at BIRD
#6 to try to improve on BIRD #5.  I saw BIRD #5 as a good evolutionary
improvement over the original and so spoke for its acceptance, and I hope
BIRD #6 will be another evolutionary improvement over it.

I think that the original spec is adequate for the "elderly" parts we talked
about at the summit.  I think that BIRD #5 gets us quite a ways toward
modelling todays parts, possibly about as well as can be by basing the model
on external measurements.  I hope that BIRD #6 will take that to the point
where one needs the vendors circuitry insights to do full justice to it.  If
that is the case it seems to fit together with the notion of levels of
compliance present ( I think ) in the die work, and I would like to see in
the ibis spec.  I am remembering that we "kinda" agreed to levels in the last
forum, but someone quick correct me if I am remembering what I want to
instead of reality :-) ( I am good at doing that! ).  I will base BIRD #6 on
that memory, if no one points up that I am wrongly remembering.

As we discussed, the topology of these busses can get pretty involved.  Arpad
( I think it was he ) came up with the idea of a tree fanning out roots on
one side and branches on the other and we start it in the middle, at the
trunk, instead of at the root as in graph theory.  That will be the central
theme of the BIRD when I write it ( which was to be Real Soon Now (tm), but I
am starting to think it should be sooner ).  This, too is an approximation,
but if we are going to go with anything less than a full Spice deck, or RLGC
matrix at the same level of detail, we simply will have an approximation. 
Also if the ground rule is that we should be able to determine the parameters
from measurements we simply will have an approximation.

More discussion is certainly welcome and invited!  I am starting to formulate
my thoughts for the next BIRD and so this is a good time to get any more
comments than we got in the forum.  I won't wait too long, though, because
the structure of the BIRD will probably spark some more comment in its own
right.

Thanks,

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