[SI-LIST] Split gnd planes - for/against?
- From: Sol Tatlow <Sol.Tatlow@xxxxxxxxxxxxxxxxxxxx>
- To: si-list <si-list@xxxxxxxxxxxxx>
- Date: Tue, 07 Apr 2009 16:36:14 +0200
I know this subject has been raised before, countless times in one
guise or another. I have also googled plenty. I'm not looking for
theoretical opinions, either, about whether or not, or when, they
should be used (specifically not, "it depends", unless you've got
REAL-LIFE examples, for and against!!!).
This subject raised its head for me in this case due to using
2 A/Ds as well as 2 D/As, both from Analog Devices, where one
specifies a split plane, the other specifies no split. Now, I am
all too wary of relying simply on evaluation boards, where, in
general, one layout is done, and if it works, that's how everyone
should do it (_without_ comparing 2 different approaches).
I personally have 3 concrete cases where split gnds had no positive
effect on SI, but significantly worsened EMC results (despite
sticking to all the usual guidelines, like no tracks over the
splits, etc.), but I have no concrete case FOR split ground planes.
So, what I'm interested in is: does anyone have CONCRETE examples
which they would like to share for/against split planes? The kind
of thing I mean would be like in one of the cases I had, where I
wanted to go against the suggested approach of using a split gnd,
and persuaded my customer to pay for 2 variants of the same board
on the same manufacturing panel, one with split ground, one with
solid ground. Both variants were assembled and tested, with regards
to both SI as well as EMC: both were functionally satisfactory; at
EMC testing, however, the split-plane bombed out big time, while
the non-split sailed through. I like to think that it wasn't due
to any screw-ups on my side, that the split ground failed - I am
not a newbie to PCB layouts, and, while for sure no professional
expert on all areas of SI, I believe I avoided the typical blunders
often present in split ground layouts.
Anyway, my customer was more than happy, but not everyone has the
money/time/desire to do as I suggested. So, any 'war stories' to
support one or the other approach would be appreciated to help
expand my knowledge and understanding of this subject - obviously,
we all respect confidentiality, so I'm not looking for circuits,
layouts and so on, but I figure many of you must have stories that
can be related regarding this subject. Or perhaps some good links
to non-confidential 'real-life' examples/studies?
Regards,
Sol
--
________________________________________
Sol Tatlow, M. Eng. (Oxon)
Product Developer
Pro Design Electronic GmbH
Albert-Mayer-Str. 16
D-83052 Bruckmuehl
Phone: +49 (0) 8062/808-302
PCFax: +49 (0) 8062/808-2302
sol.tatlow@xxxxxxxxxxxxxxxxxxxx
www.prodesign-europe.com
________________________________________
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