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I'm developing mixed analog-digital device for the first time and I'm not quite sure how to manage analog and digital power separation. The device will contain:

  • MCU
  • Digital sensor
  • ADC
  • Analog sensors
  • Wi-fi on the chip

To be exact, the module that I'm using is TA3200R1A

I can't have more than one LDO or SMPS, to physically separate them, so I've been thinking about filter.

A little research of mine showed that the best (?) option is to use Pi-filter. but I'm somewhat worrried about the resonance.

What are the best ways to separate analog and digital power?

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    \$\begingroup\$ There is no single best way, it all depends on what actual signals are going around. There is anything around there, from just star ground and proper decoupling to the need of high end regulators \$\endgroup\$ – PlasmaHH Oct 26 '16 at 9:08
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    \$\begingroup\$ As already noted by PlasmaHH, there is no single method, but there are some known practices to help: I went into some detail in a previous answer. electronics.stackexchange.com/questions/185306/… \$\endgroup\$ – Peter Smith Oct 26 '16 at 12:26
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You do not need to seperate analogue and digital supplies as such, but you do need to make sure all supplies are good enough. As digital supplies are generally noisy, and tolerant of noise, and analogue supplies tend to be quiet, and intolerant of noise, a reasonable approximation is to seperate the supplies on that basis, but it's neither necessary, nor is it often sufficient.

Filters used between the supplies can work well. Pi filters have Cs to ground at input and output, which can support large noise currents and so run you into other troubles, tee filters are generally more tame. The series elements can be inductors, resistors, or impeders, which are inductors made on a lossy ferrite that goes resistive above typically 1MHz, very handy for mopping up RF.

But the supplies are the easy bit. More difficult is the grounding, and the ground currents. The statement of what you need to do is simple, make sure that no ground currents flowing impose a voltage anywhere they shouldn't. To do that though, you need to know where they're flowing. Above a reasonable frequency (10's to 100s kHz), ground currents flow under the signal track, in response to the signal current. Don't break those current paths by gouging out slots from your ground plane.

A star ground is a commonly proposed method for dealing with multiple grounds, and will often work without understanding too much what's going on. With multiple devices however, it's not obvious how to apply it, and you need to go back to the fundamentals of ground current flow.

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