Another technique to consider is the judicious use of small,
IC voltage regulators to feed your sensitive circuitry. You
would have to take some DC voltage drop across the
regulator to provide for regulation and you would want to
isolate (split) the output power and ground planes from
your noisy system power and ground.
If your sensitive circuitry isn't too demanding of
current and you can/must afford the extra component
count, this can be very effective. You can create this
kind of isolation locally all around your system and it
usually quiets the power supply noise very effectively.
I would still provide some output capacitance and filtering
at the output of the regulator(s) because you're dealing
with switching circuitry.
Lead Support Applications Engineer
Performance Engineering Business Unit
Signal Integrity Products
Cadence Design Systems, Inc.
3 Woodfield Lakes
900 N. National Parkway, Suite 420
Schaumburg, IL 60173