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I have a DAC using MCLK from an oscillator. All literature that I read suggest to ground it to analog ground. However the output of my DAC (analog output) is also close by and I am afraid that my (48MHz) oscillator will inject noise in my sensitive audio signal.

Am I right to build a "fence" to keep the 2 analog grounds separated? Can you suggest the best way to isolate the noise?

layout block diagram

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  • \$\begingroup\$ In general, you should have the same physical ground but that may have logical analogue and digital grounds. The DAC data sheet should have some guidance on grounding. See also electronics.stackexchange.com/questions/185306/… \$\endgroup\$ – Peter Smith Oct 4 '16 at 15:50
  • \$\begingroup\$ Your best bet is to "follow the current". Try to lay things out such that the ground currents from each section flow through different areas of the ground plane. \$\endgroup\$ – George Herold Oct 4 '16 at 16:45
  • \$\begingroup\$ If the DAC logic current and the OSC logic current shares a ground return with inductive or milliohm resistance losses, then your VRef used by the DAC will also be noisy. But ensuring the point of entry for ground splits in two directions to each load analog and digital is the best way to avoid sharing currents on the same path. Yet the source is still common so it must be as low impedance at all logic frequencies to make the voltage source as ideal as possible for the separate ground plane sections. But slots between ground planes also becomes an efficient antenna for radiated noise. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Oct 4 '16 at 17:06
  • \$\begingroup\$ So do you suggest that whatever we might gain from "fencing" the oscillator will be lost because of this antenna effect ? Better then to use one ground and have multiple power planes for "1" oscilator and DAC ("2" one analog and "3" one digital) on different planes ? \$\endgroup\$ – Johan B. Oct 5 '16 at 13:35

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