Re: Package descriptions--Take 1

Howdy,

Eric Bracken writes:
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  There's been some question about what to do with the Rpin/Lpin/Cpin;
whether to lump them, and if so into how many lumps; or to model them
as (lossy) transmission lines. The transmission line models are
questionable, for the following reasons:

  The basic assumption in the transmission line model is that there's a
TEM wave propagating along the structure, which requires TWO
conductors to support it--one for the signal, and another to act as
the "return" path. A trace on a board presumably has a nice ground
plane nearby. A wire in the lead frame may too, IF the package
contains its own power/ground planes. But in the case of a bond wire
or a pin, there's no return path paired with it. You could select
another bond wire as the "return", but then the situation is so
3-dimensional that the transmission line approach is hopeless anyway.
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Actually, both the transmission-line model and the lumped circuit
model assume a TEM mode. Non-TEM implies radiative loss, which no
lumped model can account for directly. Besides, the transmission
line model is equvalent to lumped circuits if the "lumps" are
distributed in a ladder in small enough pieces.

I propose we use RLGC matricies to represent package parasitics
in the case where mutual parasitics between the pins must be
included. A banded-symmetric format for these parasitics could
be used to keep the number of entries down.

Chris Reid
cer@cadence.com
Received on Fri Oct 1 09:42:34 1993