[sdiy] split ground plane

[Eric Brombaugh]

Seb Francis wrote:

> This ties in with the other thread about using the dsPICs with built-in 
> audio DAC - it is worth remembering that uControllers are noisy beasts 
> and are never going to be producing low SNR audio without using external 
> converters.

Excellent point. The saving grace in the case of the dsPIC audio DACs is 
that they have differential outputs. Most of the digital noise will be 
common mode and thus cancel out in the summation that takes place in the 
output buffer. Such cancellation techniques usually provide about 30dB 
of rejection (depends on how well the input impedances of your buffer 
circuit are matched - even cheap op-amps give at least 60dB of CMRR), 
which would push mV-level noise down into the uV range. Not 
high-fidelity, but certainly usable for synth applications.

So - take advantage of those differential outputs when you can! It only 
costs a couple extra resistors (and you'll usually get DC coupling into 
the bargain).

Eric