[SI-LIST] : EMC Issue - servo amplifier

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From: Lum Wee Mei (lweemei@dso.org.sg)
Date: Thu Mar 23 2000 - 19:08:27 PST


I have a very small design that has a servo amplifier (module) with some
digital and analog sections. As space is a constraints, the big servo
amplifier will be on one side while the rest of the components will be
on the other. I was suggesting, at most 6 layers with L1-S, L2-S,
L3-DGND, L4-VCC, L5-AGND and L6-S. In the worst case, a very small
portion of the AGND will need to be used as DGND, if I need to place one
or two digital components with the servo amp.

The EMC engineer suggested otherwise - 8 layers. The extra 2 layers, are
for routing a crystal clock signal and its gnd plane. Another
recommendation by the EMC engineer is that this servo amplifier has to
be enclosed in a shielded box to prevent EMI. If the PWM provides at
most 16MHz, do we still require this shielded box as space is a real
constraint?

I was told in the end, all the grounds are to be shorted at one point.
If that is the case, which would be the best method to do so, at the
mating connector or within the board itself?

Any responds will be deeply appreciated.
Regards - Wee Mei

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