DACs tend to have two ground pins - digital and analog ground. It's not an insane thought to think that these should be connected to different ground planes.
Reading up on this previously, the mantra has been that you could do this, but then the two ground planes should be connected under the DAC.
While this may be fine for a single DAC system, where the DAC is the only point where analog and digital meet up, my system is definitely nothing like this. I have multiple DACs on a single card, and multiple cards in the system.
Connecting two DACs this way, with the grounds connected under both DACs, would (at least in my mind) create a ground loop which is not desireable. So what should a poor designer do?
Today I found this document:
https://www.analog.com/media/en/training-seminars/tutorials/MT-031.pdf
"Grounding Data Converters and Solving the Mystery of
"AGND" and "DGND" (MT-031)
It describes in detail how to approach this, including the multi-card issue. A short short summary is:
- AGND and DGND _pins_ should both be connected to AGND at the package
- If V_digital is not the same voltage as V_analog, V_digital should be decoupled to AGND
- AGND and DGND planes should be connected at each card through Schottky diodes to prevent a potential difference buildup
There are a lot of other considerations and preconditions that have to be met, but this at least provides some good guidelines and explanations.
Ferrite beads
One advice still troubles me a bit though. Using ferrite beads. They seem like the magical solution. The problem however, is that every DIY'er out there treat them like they are all created equal. I did read about this earlier and it seems this is not at all true - you have to know a lot more about your circuit and pick the correct bead. Without this, you just waste money and board space.
I'll see if I can find more about this later.
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