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I've read some articles that say the connection point of digital ground and analog ground should be at the power supply output port. However, when there are two or more power supplies which are physically far away from each other, I have no idea where should the connection point put.

My design is as bellow, there are three supplies which are Vcc for the digital circuit, Vcmos for CMOS camera and Vad for A/D chip. The Vcmos is generated from the DCDC while Vad is from the LDO. The ground plane is separated into two parts for GND and AGND. The distance between LDO and DCDC is around 2500mil. Now I want to put a ferrite to connect the GND and AGND. The question is should I put the ferrite near the LDO or DCDC, and why?
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  • \$\begingroup\$ I suggest you sketch out the various currents, including Efield currents from your switching power supplies MOSFETs that couple "displacement currents" everywhere. Having extremely LOW GND impedances ---- a ground plane ---- is one way to keep the GND noise very low. What is your ADC speed and resolution? \$\endgroup\$ – analogsystemsrf Jun 11 '19 at 4:46

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