[SI-LIST] Re: Need technical ammunition for switching to single ground plane !
- From: "Townsend, Fred" <ftownsend@xxxxxxxxxxxx>
- To: <gilles.aminot@xxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Fri, 21 Sep 2007 14:47:51 -0700
Hi Gilles:
I'm on both sides on this issue. This is one of the best examples of why
you should never do anything by rote rule. Over the years I have split
many planes without ever having a problem. To be fair I have also closed
splits too. I don't have problems because I analyze every occurrence.
You need to understand what is meant by a return image in a plane and
ground return paths. Often when I am working with someone I will make
paper plots of my traces and have the other person take a pencil and
trace the return paths for all high frequency and all high current
circuits. If that path has a lot of detours I know something is wrong. I
also look at the current loops. If there is a lot of area within the
loop, something is wrong.
The Analog Devices pages you refer to are good references. They offer
good solutions to difficult problems but again, don't do anything
because they tell you to. Understand the problem and you will be able to
make the correct tradeoffs.
As for where to get the basic knowledge, the SI achieves are full of
book reference. Many times the authors of those books are here to answer
specific questions but they can't do it in a general posting here.
Fred Townsend
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Gilles Aminot
Sent: Friday, September 21, 2007 2:09 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Need technical ammunition for switching to single
ground plane !
Hi Everyone,
=20
I'm working on a new design and would like to eliminate split ground
planes. In the past we've always split the analog ground plane (for
analog audio circuits and codecs) and joined it at one location
(sometimes shorting or through an inductor). I've read lot's of postings
on this group explaining good reasons not to split ground planes, but
the only real supporting documentation I have seen is the following
article:=20
http://www.analog.com/analog_root/static/pdf/raq/RAQ_groundingADCs.pdf
<http://www.analog.com/analog_root/static/pdf/raq/RAQ_groundingADCs.pdf>
and it does not provide much depth..
=20
I have been meeting some resistance to eliminating the split ground
planes and I am looking for technical articles showing the advantages of
using a single ground plane in designs with mixed high speed digital and
sensitve analog circuits. I keep bumping my head against datasheets or
articles that say analog & digital grounds should be separated (such as:
http://www.ultracad.com/articles/planesplits.pdf), which makes it
difficult to convince my peers that changing our approach is the way to
go. Can anyone share or point me to articles which may help me plead my
case. I would also appreciate if anyone could share some real life
experiences of going from split to single ground plane.
=20
Kindest Regards,
Gilles Aminot, P.Eng
Hardware Design Engineer
=20
Librestream Technologies Inc
Unit 200 - 55 Rothwell Rd
Winnipeg MB. Canada
R3P-2M5
PH: 204-487-0612 Ext 218
FX: 204-487-0914
=20
=20
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