I have a suggestion for the user interface for the impedance analyzer: remove the terminology "resistor first" or "load first" as first/second is rather meaningless in a circuit.

Instead have options

  • ch1 R+load ch2 load
  • ch1 R+load ch2 R
  • ch1 R ch2 load
  • ch1 load ch2 R

The third and fourth options would allow better measurements on the Analog Discovery 2, as the relevant voltages would be measured directly, rather than relying on the subtraction of two measurements.  Using the difference increases the noise and does not allow increasing the gain when the voltage difference is small.

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Hi @gasstationwithoutpumps

The load/resistor first refers to the following setups:

The load first circuit seems to provide better results on a wider range of frequency, extreme resistor and load impedance proportions.

I have tested the setup where C1 is used as differential (W1 C1+ Load C1- C2+ R C2- GND) but it does not bring improvements over the existing setup (W1 C1+ Load C2+ R C1- C2- GND). It is rather slightly worse, probably due to the adding of a second scope channel impedance to the middle of the circuit (C1-).
Without providing better result the implementation of this was not added to the released software.

Do you think that the following options will be easier to understand?

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I suspect that the 2-differential channels is better when the device being tested has a wide range of impedance over the frequency range, so that each of the channels will have small voltages for some part of the range, but I have not done careful tests of this.

The pulldown menu you suggest is unclear.  If you are just going to have channel 1 be the whole thing, it would be clearer to have the two options be

  • C1: R+DUT C2:R
  • C1: R+DUT C2:DUT

You could then add swapping the channels

  • C1:R C2:R+DUT
  • C1:DUT C2:R+DUT

Since it is just software, it would be good to give the options I asked for:

  • C1:R C2:DUT
  • C1:DUT C1:R

though I understand your reluctance if they don't add much functionality.

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Hi @gasstationwithoutpumps

Sorry, but I'm not sure if I can follow your suggestions. It looks like we are thinking a bit differently :)
Would the following options, that describe the whole circuit connections be easier to understand?

The measurement results with differential connection with wide range, at extreme R/DUT ratio were bad.
The best, consistent results at wide range I obtained with W1-C1-DUT-C2-R-GND 

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