I'm drawing a board with an MCU (running at 32 MHz), some serials and an analog video section (mux and amplifiers). I kept the video section physically separated from the digital one: i.e. it's placed on the right part of the board, while all digital signals run on the left. There are no digital tracks that cross analog ones.

I tried to keep video signals perpendicular to each other and, where not possible, to place among them a ground pouring to minimize cross-talk.

I'm afraid about power supply noise. The source is a DC-DC converter, placed on the left-most side of the board. From there, I routed two big traces (100 mil), one to supply the logic section and another to supply the analog one.

I think in this way the digital noise is minimized. The ground plane is the same, but between the digital and analog area is connected just in one point.

In which way I could further clean and filter the power supply trace near the analog side? By-pass capacitors along the track are enough or you would recommend some LC filter? The expected maximum current is about 300 mA @ 5V.

  • \$\begingroup\$ Is there any reason to expect the Efields of the SMPS will not couple, thru the AIR, into the video circuits? Are you planning to shield the SMPS? \$\endgroup\$ – analogsystemsrf Apr 9 '19 at 11:16
  • \$\begingroup\$ I did a remarkably similar design some years ago; provided you have quite a bit of distance from the SMPS to the video area, then this answer might be of use: electronics.stackexchange.com/questions/185306/… \$\endgroup\$ – Peter Smith Apr 9 '19 at 11:23

The Efields of the SMPS will couple, thru the AIR, into the video circuits.

Plan to shield the SMPS. Experiment with this, to be sure shields are needed.

Or shield the video circuits from the MCU and the SMPS?

Also you probably need a serious PI input filter, or common-mode choke, into the SMPS, to reduce trash currents that will find your video SOURCE and enter thru the 75 ohm coaxes.

And, as you suggested, use an LC filter between the SMPS output and your video circuits.

Using this mindset (placing inductors in ALL paths out of the SMPS including GND/RTN pins), I've achieved cleaner than 12 bit systems for avionics (air-air missile detection via IR).


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