[SI-LIST] SI Question 3 of 3: Power plane fingers over split in ground plane
- From: "John-Paul Coetzee" <jpcoetzee@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 28 Oct 2005 18:25:16 +0100
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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