[SI-LIST] Distant Reference Planes Through Other Planes
- From: "Brown, William G" <william.g.brown@xxxxxxxxxxxxxx>
- To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 17 Jul 2003 17:24:48 -0400
Hi All,
I have a scenario here where a designer wants to reference a plane through
gaps in other planes. It makes me uncomfortable, so I'd like to know how to
properly do this construction (or whether to avoid it completely) and what
the issues are.
For example, say a portion of the PCB stackup looks like this:
GROUND PLANE
SIGNAL 1
POWER PLANE (Gaps above signal routing on SIGNAL2)
SIGNAL 2 (controlled impedance signals)
POWER PLANE (Gaps below signal routing on SIGNAL 2)
SIGNAL 3
GROUND PLANE
Assuming that a relatively large gap is left in the planes, what are the
other issues which need to be addressed and looked into?
Some concerns I've thought might be applicable are what supplies are
associated with the signals, should the signals reference a PWR & GND plane
instead of two GND planes, are their return current issues and is there an
issue with having your reference planes relatively distant (30 Mils) from
the signal lines?
Any comments on this practice would be appreciated. For argument's sake,
assume we're running a couple hundred MHz with 1-2 ns rise times.
Thanks,
Bill
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