[sdiy] analog or digital ground?

[Trevor Page]

Seb,

An interesting question this, for which I'm sure many will offer a much
better answer than I can. My thoughts are, however, that the MUX GND
terminal will itself be 'noisy' due to the internal logic decoder/driver
circuitry, and therefore should be kept well away from the analogue
ground for starters. I also expect that there will be a high degree of
isolation between the GND (together with associated noise) and analogue
signals with a good MUX chip, so I'd feel safer using the digital
ground. Either that, or give the MUX a separate ground track back to
star ground maybe?

Trev


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-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Seb Francis
Sent: 10 November 2002 21:25
To: synth diy
Subject: [sdiy] analog or digital ground?


Hi,

I'm just routing the PCB for my MIDI2CV, and I've been pondering which
ground plane to connect the S&H MUX to.

It's a MAX306 (+/-V supply and analog signal range, TTL/CMOS compatible
digital inputs).  Digital inputs come direct from a PIC (so they're
pretty noisy).

My first thought was to wire the GND pin to the digital ground (assuming
there might be a bit of coupling to ground from the digital inputs), but
the datasheet doesn't give much clue whether GND is in any way
internally connected with the analog signal - the digital ground plane
is itself a source of noise.

Any thoughts?

Seb