I've connected a scope probe directly to the ground clip of the scope. I then observe the signal on the scope and it's reading 0, as expected. I set my trigger to be 1V above the 0V reading it currently has, put it to single, set the timebase to 100ns/div. At this point, i plug a standalone usb thumb-drive into the scope usb slot. The scope immediately triggers and I see a huge oscillating waveform (Vp-p about 8V, around 0V) being picked up for the duration of the 1us that is viewable on screen.

My question is, why does this happen, and can I somehow minimize the effect or prevent the scope from picking it up?

I'm using generic passive scope probes, 500MHz, 8pF, 10MOhm. I was originally trying to find any power rail irregularity, but I noticed my scope keeps on triggering with these kind of spikes. The USB thumb-stick was the best way that I can reproduce it consistently.

  • \$\begingroup\$ Are you sure you're not jostling the probe? What model is your scope? \$\endgroup\$ – Connor Wolf Apr 14 '14 at 2:33

I can not reproduce this on my scope...

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Hopefully you can see that I have the probe connected to the ground, the trigger set to 1 volt, and a USB drive plugged in and running.

I'd guess this is something idiosyncratic. I'd check your settings, check connections, try a different probe, or even maybe a new scope.

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