Different ground

[chrischina]

I am currently designing a system where there are different kind of ground in it: "normal" power ground, analog grounf, ground for sim card.

How do you advice to connect all those ground on pcb ?

Should I create one split plane for each ground and then have a single point of contact to link all those grounds ?

[danadak]

"Normally" you split grounds to minimize load current effects on analog
measurements, or to achieve noise margins for logic circuits. Take a look
at these PCB layout application notes, they should help.


https://www.dropbox.com/s/ruaf9booe17jk8n/PCB%20Layout.zip?dl=0


Regards, Dana.

[Neilm]

Based on my experience - splitting the 0V is the wrong thing to do unless you have safety issues or you REALLY know what you are doing.

Remember, current flows in a loop. I have seen (and had to fix EMC problems on) too many boards where people have followed the "one 0V for analog, one for digital" route and got it wrong. In almost all the cases - having a single 0V plane in the PCB fixed the problems. The common issue I found was that people used one power rail for the signal into an op amp, and a different rail for the power supplies for that op amp thereby creating many loops of current around the board.

I have also seen boards that work on measuring very low currents (<1pA)  that did not have a split 0V.

[Kalvin]

You may find the following document and the concept of the return current useful: http://www.hottconsultants.com/pdf_files/june2001pcd_mixedsignal.pdf