[sdiy] split ground plane

[ASSI]

On Donnerstag 07 August 2008, Daniel Kruszyna wrote:
> Well, it's been a while, but I'm now starting to work on this
> layout again. I've done a lot of reading, and most sources
> recommend to NOT split the ground plane.

That really depends on what you use the grounds for and how much 
control you have over the design of the rest of the system.

> They recommend 
> spliting the power plane instead, and keeping each set of
> signals separate in the layout.

Only you can know whether this is possible in your circuit.  
However if it is indeed possible to seperate the signals out in 
this manner, you could just as well separate power and ground 
planes in my (limited) experience.  Such circuits are rare and 
when there is a need to route over the split you have to worry 
about the impedance discontinuity that this creates (ref: 
http://www.edn.com/article/CA6578142.html ) - or maybe you don't, 
depoending on the signal.

> This board is going into a modular synth, with separate
> -15v/+15v and +5v supplies. I've tied the grounds of the two
> supplies together at their source. Might it cause problems if
> the grounds are also connected at each module? Shouldn't the
> grounds be connected at only one point?

If this is possible, you should have at least a quiet and a noisy 
ground and not connect them at the modules at all.  Even better 
if you can provide a reference ground (with no return current 
ever), a quiet ground and a noisy ground.  Since most modules (if 
they are not designed by yourself) will not have separate 
grounds, you need to decide whether they are nice enough to go to 
quiet or nasty and have to go to noisy.  If a module has local 
regulation, the voltage reference should go to reference or 
quiet, and the return current to noisy.

> Additionally, wouldn't a signal trace that crosses a split
> ground plane be simillar to a patchcord in a modular?

Yes and no.  The patchcord comes nowhere as near to the noise 
sources on the board and the source impedance is usually fairly 
low.

More reading (and there are even more links in each of those 
articles):

http://www.eetimes.com/showArticle.jhtml?articleID=18306332&printable=true
http://www.audiodesignline.com/206800872?printableArticle=true
http://www.planetanalog.com/showArticle.jhtml?articleID=207602816&printable=true


Achim.
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