Re: Bob Ward's mail on BIRD 5.1

An open letter:

Bob,

  Now that you mention it, I think "NC" is better, too. It will avoid
confusion about what has to be specified. (I'd hate for someone to
think that the pin mapping was simply unavailable...)

  Look for BIRD 5.2 with this amendment shortly.

  With regard to mutuals: I think that the issue is orthogonal to that
of the pin mapping. That is, if the pins have mutual couplings to one
another, they can be specified independently of the pin mappings, as
long as we exclude from consideration the very general network
topologies (like the one you described in that famous mail message
of a week or two ago.) The [Pin_Mapping] isn't meant to handle those
problems anyway, at least not in a rigorous fashion.

  If we come up with a spec for describing the pin-to-pin mutual
couplings (I'd still like to do this), then it's straightforward to
extend the concept of "parallel combination" to determine the
impedances seen looking out into the board from the devices connected
to the bus.

  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?

--Eric Bracken
Received on Wed Dec 15 14:35:55 1993