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I need to connect a power ground and an analog ground. The power ground is a SMPS output. The analog side consists of 8 opamps and their resistors and capacitors.
What's the best way to connect these two ground? With some ferrite beads? Resistors? Or directly connect them without any components between them?
This answer is valid if you have 1 power supply for both analog and digital parts.
The picture comes from this Analaog Devices' tutorial: https://www.analog.com/media/en/training-seminars/tutorials/MT-031.pdf?doc=CN0156.pdf
CASE 1: Double layer PCB
Route all AGND signals to the GND pole of the connector.
Alternatively, route all AGND signals to one point of the board, and then route that point to the GND pole of the connector.
CASE 2: Multi layer PCB (This is my way of routing)
Split the GND layer in 2 parts: AGND and DGND.
Route AGND to the GND pole of the connector without crossing DGND (*).
Route all AGND signals to AGND.
Usually, AGND split plane (that's the technical name) are small areas.
(*) This is what I do usually unless the manufacturer of that particular integrated circuit gives me specific instructions about routing. TI and ST, for example, write application notes that tell people how to route AGND and DGND and all the critical signals.
Since your analog circuit needs to be powered from the SMPS, you need to connect the ground of your circuit to the ground to the power supply directly. If you want to power your circuit through a low noise power supple, you can add an LC filter to the output of the PSU or use a linear regulator.
Without knowing exactly what you are doing, im assuming a pcb, from my knowledge if you need to consider EMI then unless you have specific reasons not to, you would generally use a single ground plane(s) and multiple power planes/zones with appropriate input filtering, you then separate your analogue and digital components into the different power zones
You might find this video useful How to Achieve Proper Grounding - Rick Hartley
