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Suppose I have an Voltage to Current Amplifier. And I'm characterizing it over a frequency range, can a Network Analyzer directly measure current to voltage gain (Iout/Vin)? (Or) do I have to use a resistor to create a Voltage drop to get the gain usual Vout/Vin gain?

Thank you!

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Most network analyzers require a voltage input, so you'll likely have to use a load resistor and calculate the resulting transconductance based on the resistor value.

[Edit based on The Photon's correct comment below]:

If the analyzer has 50 ohm inputs and the inputs can accept your current range without violating its specs, you can use the 50 ohms as your load resistor and calculate the transconductance from that.

If you have an analyzer with a high impedance input option, or you need to use an active probe because your current puts you outside the range of the analyzer, then you can use an appropriate load resistor.

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  • \$\begingroup\$ The network analyzer should have a 50-ohm input impedance. Putting a large value in parallel won't increase the net load impedance on the DUT. Putting a smaller value in parallel will decrease the load on the DUT and decrease the signal received by the network analyzer. \$\endgroup\$ – The Photon Nov 16 '17 at 19:22
  • \$\begingroup\$ @ThePhoton True for high frequency analyzers, but some lower frequency analyzers like the HP3562A have the option of 1MOhm inputs, so depending on your bandwidth of interest you can potentially get more signal and S/N with a load resistor. I may be wrong but this doesn't sound like an RF application so if there's an option to use an instrument with a high impedance input it may be a better way to go. Otherwise I agree with your comment. \$\endgroup\$ – John D Nov 16 '17 at 22:28
  • \$\begingroup\$ True, but it's worth mentioning that the 3562A was marketed as a "dynamic signal analyzer", not a "network analyzer". \$\endgroup\$ – The Photon Nov 16 '17 at 22:35
  • \$\begingroup\$ @ThePhoton Good point- Also we have no idea of the range of currents the OP is looking at. If it's 0-100A it's a whole different ball game than 0-1A. And in any case the analyzer doesn't do transconductance directly, it's still a ratio of voltages which will have to be converted using the load resistor (50 ohms or whatever.) \$\endgroup\$ – John D Nov 16 '17 at 22:45

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