I have been reading up on grounding and what is AGND and DGND i.e / analogue ground and digital ground respectively. Suppose , I have an ADC chip and a MCU in a PCB. Now, previously I would have a ground plane beneath them and split them into Analogue ground and digital ground. I have now realised that splitting the ground planes will be detrimental to my return path at higher frequencies of the signal.
So, the best way is to have a single ground plane or have 2 different ground plane which is connected by a ferrite bead. Then during layout remove this bead to have a thin connection between the 2 grounds.
But, this approach has an issue according to me, which might be wrong. Will this thin line not act as a sort of high impedance that blocks currents thereby making the 2 grounds at 2 different potentials ?
Best Answer
Don't split your grounds. Drop the word split altogether. Instead, use partition. Partition your grounds.
As the previous answers have stated, the purpose of this is to keep noisy digital currents away from the analog. So you partition your board, and keep all digital traces in one area, and keep analog in another.
The use of ferrite beads on PCB to seperate grounds is a hack. Dan Beeker (Freescale) and Rick Hartley have both both expressed that ferrites are for people who do not know what they are doing. Be aware of where your currents are, and you wouldn't need to use any ferrites at all.
So keep a single plane, but partition your board such that analog signals are kept away from digital. It helps alot if the IC has pinouts which make this easy.
There some good information from Henry Ott http://www.hottconsultants.com/techtips/split-gnd-plane.html
If you look at the following image
You can see that the board has been partitioned. To minimize any potential leakage, or stray feilds, there are cuts in the ground plane. This creates bridges that go from analog to digital grounds. This is ok so long as the routing ensures that no trace passes over such gaps.