Re: gEDA-user: analog/digital partitioning

[Larry Doolittle <ldoolitt@xxxxxxxxxxxxxxx>]

On Thu, Jul 22, 2010 at 09:57:11AM -0700, Steven Michalske wrote:
> On Jul 22, 2010, at 9:50 AM, Eric Brombaugh <ebrombaugh1@xxxxxxx> wrote:
> > On 07/22/2010 09:37 AM, DJ Delorie wrote:
> >> 
> >> One idea to consider is to start with a solid plane, and cut slots
> >> around the sensitive analog parts, like big C shaped moats, squares
> >> open on one side.  You retain the "big ground plane" conductivity, but
> >> you prevent stray currents from using your analog area as a short-cut.

Now each side of this debate can call you a heretic -- that's a good thing!
I'm generally on the single-ground-plane side of this fence, and the
one time I ran into trouble, the solution was just as you describe.

> > Just make sure that if you've got high-speed digital lines that cross into the 'cubicles' they have gnd plane underneath them where they enter - don't let fast signals cross the cuts because then the return currents have to take a different path and that will screw up the signal integrity.
> > 
> The question is "how fast?". Because you loops may not even matter.  But just remember to keep them small. :-)

If you have _any_ signals crossing the slots, you're doing it wrong.

   - Larry


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