Dennis,
        Yes, although he is an engineer, he knows what he's talking about.  The general idea of moating is to keep noise from a noisey section in that section and not let it "escape" into the rest of the circuit.  This is a fundamental of high speed design practice and design for EMI.  Things to keep in mind while doing this are: don't cross the moat with any traces or planes, include ties to ground in this area, (vias or pins to ground), pull back the power planes from the moat edges of the ground planes, and don't isolate the area completely (provied a "bridge" for any signals coming in or going out).  You may want to go around the interior perimeter of the moat with stitching vias tied to ground to further isolate noisey section from the circuit.

                                                                                Good luck!


Robert Butterworth
Sr CAD Design Engineer
ADC
11 Fairfield Blvd
Wallingford, CT 06492

-----Original Message-----
From: Dennis Ward [mailto:[log in to unmask]]
Sent: Friday, April 28, 2000 10:26 AM
To: [log in to unmask]
Subject: [DC] Moats


Good morning everyone,

Plese bear with me on this one. Basically an
engineer and I are having a p!##ing contest
concerning moats.

On the design he wants a "moat" placed on the
ground plane around certain power pins.

Now this moat is NOT an isolated plane. Basically
it is a long "U" shaped slot in the ground plane.
His reasoning is that it keeps noise from coupling
onto the pins.

Does anyone practice this? I understand isolating planes,
especially analog/digital circuitry. However this slot
in the ground plane does not make sense to me. The
pins aren't not truly isolated from the plane.

Now I've looked in the "High-Speed Digital Design" book
and didn't find info on this subject. Plenty on crosstalk
over slots, how to moat (true moats) and things of that
nature. I've looked on the email archives and checked out
a few web sites. Still no definite answer. Someone please
enlighten me.

Thanks
Dennis