How can I set the oscilloscope probes as matched probes (R&S HMO3002)

[ogulcan]

Hi,

I want to test the switching regulator output of my circuit using the simple methodology described in the page 18 of http://www.ti.com/lit/an/snva559a/snva559a.pdf,
which is attached as remove-common-signal.PNG.

I have a Rohde&Schwarz HMO3000 series (HMO3002) oscilloscope, and I could not make my probes matched, so when I substruct the channel 1 signal from channel 2, I cannot get rid of the spikes, which I think is due to the fact that my probes are not matched probes.

How can one set two oscilloscope probes as matched probes?

Cheers,
Ogulcan

[David Hess]

This was easier to do with the analog oscilloscopes and the oldest DSOs which did the invert and add in the analog domain.

You can evaluate lots of probes to find the best matched set but keep in mind that the oscilloscope vertical inputs contribute their own mismatch so the probes always need to be attached to the same vertical inputs.

In practice the best compromise is to use 10x probes and:

1. Apply suitable common mode square wave signal.
2. Adjust the compensation of each probe.
3. Switch to invert and add mode so the test signal becomes common mode.
4. Adjust the compensation of one probe and the vertical gain of one channel for best common mode response.

Note that x1 probes have no compensation adjustment but the vertical gain adjustment still needs to be done because of gain mismatch between the vertical inputs.

[ogulcan]

Thanks for your answer.

It says 1:10 on the connector of my probes, so I guess they are X10 probes, I saw a hole in the connector of the probes and tweek it a little bit, it changes the amplitude, but does not seem like changing the compensation.

You can see the probes I'm using in here: https://www.tequipment.net/Rohde-&-Schwarz/HZ355/Standard-/-Passive-Oscilloscope-Probes/

I guess I need a matched set 

[David Hess]

In order to see the compensation, a low frequency square wave test signal is required.  1kHz is typical.

After compensating the probes, the same or higher frequency test signal is applied to both and the compensation and vertical gain of one probe is adjusted in differential mode for the best or least common mode response.