Subject: EGG1.0 : Mutual pin parasitics

From: [email-masked] (Christopher E. Reid)
Date: Thu, 16 Dec 93 09:00:40 -0500

Hello,

Eric's mail on mutual pin parasitics asked where the capacitance
should be, on the inside or outside of a pin. Actually it does not
make much difference. Either way the circuit has the same transfer
function.

As for representing mutuals, we are using banded-symmetric RLC
matricies. That is the form most 3-D field solvers deliver the result,
and it is an easy format to deal with in software. Eric's suggested
format is up to the task, but it is somewhat more verbose than
required, and requires more processing by the software.

We added a key-word to the IBIS spec, [PackageModel], which specifies
a package-model (RLC matrix) to use by name instead of putting the
data directly in the pin-map. This was done because many devices may
share the same package. In otherwords, a TI_DIP16_PLASTIC package may
be used for many different IC's, but the package-model is entered in
our library only once.

If the [PackageModel] is specified for some device, the RLC parasitics
in the pin-map are ignored in favor of the diagonal entries in the
package-model matrix.

I will write a BIRD for this one.  The pertinent section of Eric's mail:
-------------------------------------------------------------------------
  In fact, now that we're talking about it, here's an EGG (even
earlier than a BIRD) on how to do mutuals:

[Mutuals]	Pin1	Pin2	Rmut	Lmut	Cmut
		1	2	1e-3	1n	1p
		1	3	1e-4	0.1n	0.1p

Columns "Pin1" and "Pin2" contain numbers of pins which are coupled
together; the Rmut, etc. columns specify the values of the couplings.

Not every coupling must be specified (in the interest of sparsity);
you can assume that the self-inductances have been specified in the
[Pin] section (talk about backward compatibility!)  And it all fits
into 80 characters.

The only thing I'm not sure about here is where the C is; is it on
the "outside" node (close to the board) or the inside node (near the
die)?  

Kumar, or Chris, do you have an opinion on where C should be?
-----------------------------------------------------------------------