I have built an analog circuit PCB that I want to debug. It has to get a bipolar power +-5V and an input sinus signal. The signal on the CUT (circuit under test), has buffered inputs (but a common ground on an entire PCB).
Only issue is that I don't have a dual PSU at hand (only a single output one). Thus I got an isolated +-5V DC/DC converter, et decided to try with that.
Circuit basically works, but I've noticed that signal generator influences the power rails (basically generated sinus wave gets 'induced' directly into the power rail as noise with much lower amplitude).
So I've figured something is not right how the equipment is connected together. Namely the return path could cause this noise?
This is what I think is going on:
The PSU and SignGen GND's are effectively connected to the mains Earth.
1) I was wondering If I could reduce/remove this artifact when I connect signal generator ground to the PSU output's 'Negative' terminal ?
2) Should I make some other connection to remove possible ground loop ?
3) How would I need to connect an oscilloscope to avoid making a second ground loop to mains earth again ?