Re: [SI-LIST] : Hopefully not a controversial question ...

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From: Doug McKean (dmckean@corp.auspex.com)
Date: Thu Feb 24 2000 - 13:55:29 PST


mbenson@wavecrestcorp.com wrote:
>
> Can someone explain what this technique is??
>
> Thanks,
>
> Mike Benson

Well, since I raised the question, I'll try.

Essentially take a cookie cutter and cut out an
"island" leaving one small amount of material to
act as a "bridge". Usually the power and ground
planes. The void around this island is the "moat".
If you held the board up to a light, you'd see
light shining through the fr-4 material. Traces
to and from the circuitry on the island is brought
across only on the bridge.

The idea is to separate an otherwise noisy ground
plane from an area that might otherwise need less
noise. An ASCII form would be something like

          Main Gnd/pwr/sig planes
      +-----------------------------+
      | voided area |
      | +--------------------+ |
      | | Isolated | |
      | | GND/PWR/SIG | |
      | | Planes | |
      | | | |
      | | B | |
      | +------+ R +-------+ |
      | | I | |
      +----------+ D +------------+
                    G
                    E

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