Tobie Horswill wrote:
....
>     I've just started working on an audio project involving an 16F877 and an
> Analog Devices SSM2160 (requiring a  -6V,+6V supply). Any hints on how the
> two supply voltages should be generated and routed on the PCB in order to
> minimise digital leakage in the audio ? I know this isn't a great idea but
> if possible I would be using using a small +5V, +12V laptop computer style
> switching supply. How can I best isolate the circuit from the switching
.....

Chris Eddy wrote:
....
>
>So you also need a negative voltage.  You can use one of those 7660 style
chips,
>but many folks find that they have terrible noise.  The other possible solution
....

Tobie,

As a voice of experience with 766x parts, I can definitely say, "yes,
they generate terrible noise". If using these parts in a pcb layout,
be *certain* to include a ground plane under the part. On a mockup, you
can use aluminum ducting tape underneath [grounded, of course]. Also,
you would want to locate your low-level pre-amps on the other side of
the board, as far as possible from the SMPS and 766x, to minimize pickup
of radiated EMI.

Also, if this is a "hi-fi" audio type project, mixing analog with
noisy digital PICs and SMPSs and 7660s is going to be a real problem,
no matter what you do. Possibly, use separate analog/digital boards
with shielding in between.

best regards,
- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom
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