[SI-LIST] Tradeoffs of split power plane vs. multiple power layers....
- From: "Jon Anderson" <jon@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 06 Apr 2006 03:42:12 -0000
Greetings.
I am curious to get some insight/opinions on power distribution
approaches and the benefits of various configurations from an SI
standpoint. Specifically, I am wondering how a split power plane
within a single board layer affects SI, and the best methods for
mitigating integrity issues (for example the use of multiple ground
planes, or don't do split power planes since it's an SI no-no).
It may be best to present an example. It is not unusual to see
separate power (or ground) planes for analog and digital sections of
a board. This is obviously done to provide isolation and limit the
effects one section has upon the other. I am considering the
tradeoffs of using multiple supply voltages/planes within a single
board layer (which may be necessary in the case of an ) versus having
to do unique layers for each voltage. Such a configuration might be
necessary in the case of an ASIC that has multiple supply voltages
but a common ground reference. Also, is it best to use matched
power/ground layers for each voltage, even if the grounds are
commonly referenced? If you do a split plane, are you as concerned
with separate ground planes for each voltage?
I understand that there are non-SI benefits to limiting the number of
board layers (cost is the obvious one), but I'm strictly looking at
this from a signal/power integrity standpoint. I also understand
that the answers are likely application dependent, so I'm just
looking for generalized reasoning why a specific configuration may or
may not work well. I fully realize this is a series of very open-
ended questions.
For sake of arguement (and to simplify the situation), let's say that
you can route all signals on the top and bottom layer, so any
internal board layers would only be power or ground planes. I
realize that the question becomes more complicated if you are looking
to have internal ground planes specifically for isolation of signal
planes.
Thanks in advance.
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