What should I take into account when designing a PCB with two different grounds? Let's say power ground and signal ground. I've heard of the use of ground planes. But if I have two grounds, would I have to create two ground planes? Or what would be a good way to distribute the grounds over the two layers? I've designed small PCBs for simple applications and this is not a problem. Now it's my first time designing a more complex one.

 

A couple references:
http://www.analog.com/en/analog-dialogue/articles/staying-well-grounded.html

http://www.ti.com/lit/an/slyt499/slyt499.pdf
http://www.ti.com/lit/an/slyt512/slyt512.pdf

 

What I do is totally separate the low level logic from the power side circuitry as much as possible, but often set up a separated ground plane for each where practical.
Max..

 

Here is the ground plane from one of my BLDC boards. I know this is a 4 layer board but the same thing can apply on a 2 layer board.
There are 3 areas, and all are connected together at one point.

Usually at the main power supply capacitor 0V.
The idea is to keep the different currents apart.