Re: gEDA-user: pcb via and ground planes

[Gene Heskett <gene.heskett@xxxxxxxxxxx>]

On Friday 25 September 2009, gene glick wrote:
>DJ Delorie wrote:
>> I talked with Dan about it, we seem to think it's better to not use
>> the ground plane for the return signal, and route the return the same
>> way you route the audio.  Think of it like a differential pair.  That
>> way, you get current balancing without breaking up your ground plane.
>> Also, avoiding vias helps ;-)
>
>You know what?  There's merit to this approach - thanks for the idea!

Lots of merit, based on my experience as a broadcast engineer trying to get 
poorly designed stuff to perform as the chip books spec say it should.

Doing this encourages the emphasis in the star ground topology.  The nearby 
ground plane should help to reduce induced noises unless there is a heavy 
power stage also making that ground plane bounce around.

A very good idea indeed.

>After thinking about it a bunch, this may work out fine.  It's
>definitely not what I originally envisioned.
>
>The only 'trick' here, when running those differential pairs, is to be
>certain the return current actually flows in them and not the planes.

One should not allow a connection between your 'ground' run and the ground 
plane except at one common point for all such runs.  I have all the wiring 
for my emc driven, stepper motor moved milling machine setup that way 
including shielded motor leads, grounded at one end only, and I can even do 
electro discharge machining with it, using an 80 volt supply at about 4 amps 
with a 10 uf oil in a can paper capacitor, loud enough to make your ears ring 
if you get too close to it, but it never lost or gained a step in a rather 
lengthy session of drilling holes with it a few months back.  Sweet holes 
too, absolutely burr less.

-- 
Cheers, From another Gene
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