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If you are trying to observe a relative small voltage across a shunt resistor and you are finding common mode noise interference induced in the signal, in what cases would you choose to use something like a differential to single end amplifier across the shunt VS. a common mode choke?

Would a diff-amp topology be used for smaller (instrumentation?) signals in the mV range and a choke for "power supply level" voltages?

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If you are trying to observe a relative small voltage across a shunt resistor and you are finding common mode noise interference induced in the signal, in what cases would you choose to use something like a differential to single end amplifier across the shunt VS. a common mode choke?

You might use both; the CM choke would be used (in conjunction with small value grounding capacitors) to reduce high frequency common mode noise and the lower frequency stuff is handled by the differential amplifier (with appropriately sized-in-value input resistors). The CM choke is to prevent the op-amp having to try and cope with really high-frequency stuff that it is ineffective at dealing with.

Would a diff-amp topology be used for smaller (instrumentation?) signals in the mV range and a choke for "power supply level" voltages?

A diff amp can be used for any signal levels that are within the design range chosen. Outside the design range of common-mode voltages, the diff amp would become fairly useless.

CM chokes are also used for power supply filtering.

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  • \$\begingroup\$ I realize you said "VHF" signals...but does this also correlate (in real world applications) to higher amplitude(s) as well? Eg. obviously some high power spikes (caused by VFD's or celluar etc) can reach very high voltage peaks (relative)..is this something that would saturate an amplifier only if it did not have something like a choke to damp some of the "extreme" levels of noise? ("generic" opamp anyway obviously would depend on the model characteristics) \$\endgroup\$ – Matt001 Dec 7 '20 at 14:47
  • \$\begingroup\$ I never mentioned VHF at all. I did say this: A diff amp can be used for any signal levels that are within the design range chosen. Outside the design range of common-mode voltages, the diff amp would become fairly useless. - if the spikes are within the CM range and not too fast then the diff amp should cope. \$\endgroup\$ – Andy aka Dec 7 '20 at 14:49
  • \$\begingroup\$ Sorry I was referring to your comment about "really high frequency stuff" under the umbrella of "VHF" (cellular and above ~30MHz) \$\endgroup\$ – Matt001 Dec 7 '20 at 14:52

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