Re: gEDA-user: pcb, howto partition power planes?

[Larry Doolittle <ldoolitt@xxxxxxxxxxxxxxx>]

John -

On Tue, Oct 28, 2008 at 10:11:38PM -0500, John Griessen wrote:
> Larry Doolittle wrote:
>  > I have seen exactly one case where a "split" (very carefully done)
>  > on the ground plane was needed to avoid a source of ground return
>  > crosstalk.
> I'd like to hear more about that, if you will.

The ADC and its input connector (vertical SMA) were in the middle
of the board.  On one side was a power supply, and on the other
some variable load (I forget what, maybe a DAC).  Low frequency
return currents travelling along the ground plane created (with
Ohm's law) voltages that mimicked changes in the input pin.  The
ground plane needed a "C" shaped cut, with the SMA and its four
ground posts in the middle and the ADC input on the right, to keep
the interfering current away from the signal, or more precisely
its return path.

I hope that made sense.  It was hard to find, but pretty clear
to us after the fact.

   - Larry


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