[sdiy] analog or digital ground

[Seb Francis]

Hi,

Thanks for all the replies to my question.  I have decided to use (a) DGND for the MUX GND pin, but (b) decouple the +/-V supply pins to AGND.

My reasons for (a) are:

- GND pin on MUX is used only as a reference for the digital logic inputs, therefore there is likely good isolation between this pin and the analog signals
- The switch rate of the MUX is quite high, so the digital section is likely to produce some high frequency digital noise
- The digital logic lines from the PIC are noisy, so possibility of coupling from them onto the analog ground should be avoided
- 2/3 synth-diyers said use DGND

My reason for (b) is:

High frequency noise on the supply rails can couple into the analog signals due to the FET gate capacitance, therefore the power needs to be as clean as possible relative to analog ground.


Seb