Power Plane Impedance
I've had to design a FPGA circuit board as part of my job. The
board has high speed digital logic and low level analogue circuits
and some switched-mode power supplies. I was quite concerned in
case the board suffered from noise problems and so I read various
engineering
articles on the topic of signal integrity. However,
I found that the material offered conflicting advice. For example, some
people say that decoupling capacitors should be placed close to IC packages
and others say that at the frequencies at which the decoupling capacitors work
as capacitors, the wavenumbers are relatively large, so the location
of the capacitors is unimportant. In order to clear up these conflicts
in my own mind, I studied the problem using Maxwell's equations and used
the insights gained from the field solutions to make a circuit model
which I've followed in my design work. I've written this up as a
whitepaper on power plane impedance together with the
Scilab programs
to do the calculations which can be downloaded below. I'd appreciate
critical feedback on this work; my job is in a small company and so
there's little opportunity for technical debate over these issues.
File Last Modified Description
vector-helmholtz.sci 15-Feb-2008 Analytic solution for impedance of circular board
method-of-moments-v5.sci 15-Feb-2008 Numerical solution for impedance of a general board
power_plane_circuit_model.sci 15-Feb-2008 Circuit model for power plane impedance
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