Switched Capacitor - analog or digital ground?

[arefeidi]

Hi,

when buliding up a switched capacitor filter circuit (e.g. with a MAX267 or MAX293), should the SC-filter IC share the same ground plane with the analog circuitry, or would be recommendable to give it a separate ground (=digital ground, which is then connected to the analog ground at one point)?

I'm not really sure, as switched capacitor filters somehow are analog AND digital.

 

[arefeidi]

No one has an idea if it would help reducing noise to use a separate ground?

 

[kevpat]

It is difficult to give a definite answer without knowing the application you are using the filter for and what else is in the signal path. One thing I would suggest though is keep the same ground that is used in the other areas of the signal path i.e if the path has an analog amplifier before the filter and say an ADC after then you obviously connect the gnd to analog gnd.

 

[LvW]

No one has an idea if it would help reducing noise to use a separate ground?

Hi arefeidi,

instead of giving a detailed answer I can recommend to you the following link

https://www.epanorama.net/wwwboard/messages/1942.html

More than that, enclosed please find a pdf document from B. Baker - an experienced analg/digital designer (female !).
Regards

 

[arefeidi]

Thanks, very well written document.
I was just not that sure how to treat the SC-filter - digital or analog. But after some more reading I think I can connect it like an analog element.

 

[LvW]

Indeed, S/C circuits are something "in the middle" between analog and digital: continuous in amplitude, but discrete in time; calculations are based on the mathematical methods of digital signal processing (discrete FOURIER transform)
The correct term is "sampled data systems".