[SI-LIST] SI Question 3 of 3: Power plane fingers over split in ground plane

Last question!     ...for now...

I am working on a telecoms design with Analog and Digital areas.  The =
whole unit is inside a thick=20
metal box, with the PCB bolted and grounded to the chassis across the =
board.  Various parts of the=20
PCB are also further isolated by slots in all the ground and power =
planes and also by metal walls=20
bolted to exposed ground plane on the top and bottom of the board.

Here is an ASCII picture of small part of the board showing a digital =
area, analog area, the slots=20
isolating those areas and the soild metal wall. You will only be able to =
see this picture properly=20
in monospaced font

There is a thick power plane trace crossing this slot to provide power =
to components in the analog=20
zone.

What are the risks of the power trace crossing the slot?  Particularly =
with respect to degradation=20
of noise margin in the analog zone.



|                             #########                   D I G I T A L  =
 G R O U N D
|                             #########
|                  +---------+#########                   =
+--------------------------
|                  |         |#########                   |              =
           =20
|                  |         |#########                   |              =
           =20
|                  |         |#########                   |         S L =
O T         =20
|                  |         |###   ###                   |              =
           =20
|                  |    S    |### W ###                   |              =
           =20
|                  |         |###   ###                   =
+--------------------------
|                  |    L    |### A ###                   =20
|                  |         |###   ###
|                  |    O    |### L ###
|                  |         |###   ###
|                  |    T    |### L ###                   A N A L O G   =
G R O U N D
|                  |         |###   ###
|                  |         |#########
|                  |         |#########
|     ------------------------#########---------------------=20
|                             #########                      Analog =
Power trace (thick)
|     ------------------------#########---------------------=20
|                  |         |#########
|                  |         |#########
|                  |         |#########
|                  |         |#########
|                  |         |#########
|                  +---------+#########
|                             #########
|                             #########
|                             #########
+------------------------------------------------------------------------=
------------

--
JP Coetzee  (was JP Nicholls) /  jpcoetzee@xxxxxxxx =
<mailto:jpcoetzee@xxxxxxxx>=20
=20
Digital Design Engineer
=20
Powerwave UK Ltd
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