Cons or pros related to connecting analogue and digital grounds together using a ferrite or inductor
I have designed and built boards with mixed analog and digital, and they do have separate ground planes. (I used a 4 layer board) The ADC converter had separate analog and digital ground pins. (it was an LTC1605IN) This is the point were Agnd and Dgnd were joined with a very short jumper wire. ALL analog sources were analog grounded at their inputs, including any shields for shielded pairs, as I often used 600 ohm STP (shielded twisted pair) to keep noise pick-up and common mode DC offsets to a minimum. The Analog power supply used a small pc mount DC-DC converter to provide isolated +/- 15 Volts. In some cases I just use LM7805 and LM7815 and LM7915 linear regulators, so the power sources had the same source ground(at the power supply), but did not junction on the board except at the ADC converter. It keeps the separate ground planes apart until they HAVE to join. The best place is the ADC converter, to prevent up-stream op-amps from picking up digital noise on the analog gnd trace. After the analog signal become digitized, they are standard logic '1' or '0'. The digital logic IC's and CPU / MPU are much less sensitive to noise because an input has to cross certain thresholds at least 500mV to 4 volts apart before it is considered a logical '1' or '0'.