Excellent writeup and project! Would buy one immed but had some significant family medical costs in november. Tucked the info away for hopefully the near future. Thank you again, this will be very useful!
J
Patrick Coleman wrote:
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To revive an old thread, I wanted to give an update on the power rail probe project - I built out the prototype in October and spent the last few months characterising it. It works pretty well!
The frequency response (attached) is flat to 500MHz, as hoped, aside from a -3.7dB dip @ ~1.2MHz. That had me stumped for a long time, but after messing around in TI (TINA?) SPICE I believe it to be poor compensation in the inverting opamp U2 (see GitHub below for schematics).
I have some ideas for improvements, but the probe works really well for day-to-day use, and the frequency response is now well characterised should you wish to take more accurate measurements. I've attached a chart of 20mV p-p noise on a 20V rail from my bench PSU, taken with my cheap 10MHz Picoscope thanks to a 20V offset applied by the power rail probe.
My plan is to release the 8 boards I have here as v1.0 (with fancy machined front and rear panels, no less), and continue iterating on the design as time allows.
There's a detailed writeup on GitHub: (there's also a link there to purchase an assembled unit, or a blank PCB, both shipping from London, UK)
...and some more colour in this thread on Mastadon:
I really appreciate the detailed advice and feedback from the group back in August - it influenced and improved the design. If you get in touch directly, I can add a discount to your order (anyone on the group is welcome).
Finally - I'd really like to verify the noise measurements I've taken, because I'm not sure I entirely trust my setup(/methodology) here. If you happen to have access to a good spectrum analyser and well-characterised noise source, with the ability & patience to measure noise down to say -100dBm, and would be willing to measure the noise power across a bunch of frequency bands, I'd love to get in touch. I can pay you ... in power rail probes :^)
Cheers
Patrick
