Connecting Digital ground and Analogue Ground

Hi all,

I have fabricated an electronic board which includes RF (2.4 GHz), IF and also digital part. I have separated the analogue and digital ground from each other except one point which can be shorted directly (DGND to AGND) or connected via a ferrite bead (DGND-ferrite bid - AGND). Which one do you think is better?

Cheers
Hadi

Hadi-Alik said:

Hi all,

I have fabricated an electronic board which includes RF (2.4 GHz), IF and also digital part. I have separated the analogue and digital ground from each other except one point which can be shorted directly (DGND to AGND) or connected via a derrite bid (DGND-ferrite bid - AGND). Which one do you think is better?

Cheers
Hadi

Click to expand...

Between those two options, I'd opt for the single-point ground node using a piece of metal to short the two grounds together. Using a ferrite bead can introduce a resistance, which could generate a voltage difference in your ground planes and create a ground-loop/level-shift problem.

If you wanted to keep a common ground on the entire board, you could use a "ground wall" implementation, where you use two large areas to separate the digital and analog circuits. Between the two sections, you create a "wall" of vias to trap errant signals from crossing between the two areas (spacing < lambda-min/10). Any place where signals cross the boundary, you run a strip of metal through the wall of vias. This way you have a good signal return path located directly above/below the signal conductor. To prevent unwanted signals from coupling onto the traces crossing the boundary, you just need some simple two-element filters on either side of the "wall".

Thanks a lot
I think you are right, It is better not to risk ..

Hadi

Digital ground and analog ground are nodes of network. And using that is not a risk but good.