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What is Common Mode Rejection Ratio (CMRR) and how to measure it on a high voltage differential probe or differential amplifier. Using the new Rohde & Schwarz MXO4 oscilloscope.
https://www.rohde-schwarz.com/us/products/test-and-measurement/oscilloscopes/rs-mxo-4-oscilloscope_63493-1164992.html
Extended 30min version: https://www.youtube.com/watch?v=4gi2B3LrCww
Differential Probe How It Works: https://www.youtube.com/watch?v=GOlgaEK2Hsk
High Voltage Probe reverse engineering: https://www.youtube.com/watch?v=GOk1BYKSsOI&t=2s
Oscilloscope Standard Deviation noise measurement: https://www.youtube.com/watch?v=G8Qoj3TpO9A
Use coupon code ProbeyMcprobeFace for 15% of the HVP70 differential probe:
https://www.eevblog.com/product/hvp70/
Forum: https://www.eevblog.com/forum/blog/eevblog-1521-how-to-measure-differential-probe-cmrr/
00:00 - What is CMRR?
01:53 - Why twist the wires?
03:26 - Typical CMRR figures
04:51 - How to measure CMRR - The Setup
08:54 - Remote R&S Oscilloscope desktop view & settings
11:22 - Output to input voltage ratio
11:58 - Beware of DC offset
13:36 - Does the 20MHz CMRR measaurement match?
14:02 - Input referred measurement
15:02 - Compensating for the gain
16:29 - Automated Frequency Response Analysis
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#ElectronicsCreators #CMRR #Tutorial

By YTB

23 thoughts on “Eevblog 1521 – common mode rejection explained measured cmrr”
  1. Avataaar/Circle Created with python_avatars Dardo Sordi says:

    This is really great stuff Dave! I loved every bit of it, it's well polished.

  2. Avataaar/Circle Created with python_avatars GoBO207 says:

    I know this doesn't make sense, but I actually prefer looking at the scope from the cameras perspective rather than the screen capture. Wouldn't be the same for a smaller scope, but for this one…

  3. Avataaar/Circle Created with python_avatars Jim Haldeman says:

    One-of my first projects in electronics as a design tech was to build a common mode amplifier. For the life of I had no idea what there was to achieve expect build an amplifier that had a gain of 1 or less. The cathode follower ! I used an RCA low noise high frequency 6DS4.

  4. Avataaar/Circle Created with python_avatars q zorn says:

    I love these kind of videos. They make learn and relearn things I have dealt with for some time. 😎 Thanks and happy 2023 new year. 🥳

  5. Avataaar/Circle Created with python_avatars jassim javed says:

    Thank you Dave for educating us!

  6. Avataaar/Circle Created with python_avatars OvalWingNut says:

    Did I win the scope? I guessed 42 Send to Long Beach, CA. USA, 3rd house on the right. THANK YOU!

  7. Avataaar/Circle Created with python_avatars Joop Terwijn says:

    Guess you need to put the whole setup in a faraday cage to reject as much noise as possible

  8. Avataaar/Circle Created with python_avatars uLearn says:

    Dave, you should make a note that you’re measuring CMRR from input to output (the smaller, the better), while the formulas you show and what you describe display CMRR as the ratio of differential gain to common mode gain (the larger, the better). I can see an astute viewer being confused. Otherwise, great video.

  9. Avataaar/Circle Created with python_avatars electronics unmessed says:

    👍Wow, pretty advanced features that you are explaining here! Many thanks.

  10. Avataaar/Circle Created with python_avatars Amrish Hirani says:

    Merry Christmas

  11. Avataaar/Circle Created with python_avatars den2k88 says:

    Too late to ask Santa this gorgeous oscilloscope

  12. Avataaar/Circle Created with python_avatars guillep2k says:

    Why Ch1 changed from 1.75V to 1.80V when changing frequencies? The attenuation in the circuit should be linear, right?

  13. Avataaar/Circle Created with python_avatars Alex R2AUK says:

    👍 🔥

  14. Avataaar/Circle Created with python_avatars messageobliquespe100 says:

    I’m sorry – I’m just gonna say this subject is hocus Pocus – as well as that gadget measuring it -& that fancy microwave with a funny picture on it. Hocus Pocus.

  15. Avataaar/Circle Created with python_avatars Paul Cohen says:

    Good but TOO LONG.

  16. Avataaar/Circle Created with python_avatars Ryan E says:

    I never got a satisfying answer to what "common mode" noise was. I always saw CM chokes and wondered why they were needed.

    My understanding is common mode is simply a signal that it applies to all input lines (without prejudice). Further, since lengths of wire are effectively antennas, they can pick up high frequency interference which a choke will filter out due to the magnetic flux, which differential signals will pass through due to the topology of the choke and its windings.

    This video seems to confirm my understanding. Is there any additional nuance that I'm missing?

  17. Avataaar/Circle Created with python_avatars Ghl Scitel says:

    A transformer can be used as differential probe. Did you ever measure the CMRR of e.g. an Ethernet transformer?
    Citation: "All the grounds of the inputs are common"
    That is not completely true. It may only be true if you have no ground loops.

  18. Avataaar/Circle Created with python_avatars Serg Gorod says:

    Очень в тему! Just in time!

  19. Avataaar/Circle Created with python_avatars Optron Cordian says:

    For me, a real test is to solder both inputs together on the board and then measure. Now the output can result from the difference in length and position in the twisted pair of the probe wires. However, it is not worth the effort considering the very high rejection ratio even without that.

  20. Avataaar/Circle Created with python_avatars NeverTalkToCops1 says:

    Today, Daiyve demonstrates a set up where the probe costs LESS than the oscilloscope!
    Just grab that R & S scope for $23,632.

  21. Avataaar/Circle Created with python_avatars IanScottJohnston says:

    Very nice explanation Dave, enjoyed this one very much.

  22. Avataaar/Circle Created with python_avatars PushyPawn says:

    Kamagatza 🥷

  23. Avataaar/Circle Created with python_avatars like dot audio says:

    Can you do balanced audio with these?

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