FEDEVEL
Platform forum

roland.lawson , 07-29-2019, 07:05 AM

Hello Robert,

I would like your inputs on how to mitigate noises on a mixed-signal pcb design. I am trying to design a small "data acquisition" and I am debating if i need to isolate the input voltage side, the digital side, and the analog side. would a 2-layer boards work? I am thinking 4 layers ( signal, gnd, vcc, signal). if I were to isolate the boards, should I use polygon pours or/and also add gnd separations on the dedicated ground plane?
do you have any tutorial that talks about isolation?
Thanks,
Roland

robertferanec , 07-31-2019, 07:08 AM

I do not have any tutorials on this topic, also it is not something what I normally design. I have designed some IO boards and in these cases I tried to isolate the analogue inputs as much as possible from the digital parts.

I am not sure how sensitive your inputs need to be - more sensitive, more critical the design will be.
- For less sensitive analogue circuits I simply use single GND plane and I am careful to place analogue parts into "quiet" corner, not mix it with digital stuff and away from high current paths.
- For more sensitive circuits, I design the parts of the PCB basically like a separate PCBs (when you pick up the PCB and have a look through the PCB to a light, you will see, that the circuits are completely isolated - there is no copper connecting the analogue part of pcb with digital, except the place where the AD chip is placed or which is needed for making unnecessary connections) - its basically like placing several individual PCBs on one big PCB with a gap for example 1 to 5 mm (depends how much space I have).

But, as I said, I am not expert for analogue, so maybe would be the best if someone else will advice or maybe google around.