I'm working on a project were we are making PCB for measuring weight with 24-bit ADC (AD7792), MCU and GSM module.
Because those measurements are highly sensitive, we are considering AGND and DGND separation.
I know that for this project most of you would recommend 4 layer board, but due to some circumstances (long story) we can make it only now in 2 layers.
So my questions are:
- When we use ground plane on bottom layer, are there any benefits of using ground pour on top layer where signals our routed? In case of AGND and DGND planes on bottom side, is it good to even have a ground pour on top side because of coupling noise with AGND on bottom?
- I saw on OpenScale board (https://www.sparkfun.com/products/13261) -> under the documents, eagle files, that they route signals under both side. Is it a good practice to route few cm long traces on ground plane?
- Also on that board I saw that they are connecting top ground pour to every ground pad. Is it good idea? I thought that ground pour is only here to curve electric filed (reduce crosstalk) and that no return current should flow through it. And that return current should flow on ground plane underneath signal trace to cancel magnetic filed of above signal.
- How should ground pour be connected to power supply gnd? Is it grounded to bottom ground plane with vias? In that case how to avoid "strange" currents paths when we are doing ground plane separation?
P.S. Sorry if my question are confusing and in some term repeating, I'm so confused with all this in that case that I can't even write concise question 🙂