A SQUID (Superconducting QUantum Interference Device) can be used as a magnetic flux to voltage converter. A DC current biasing I_SQ=I_0 is usually apply. Looking at the I_SQ(V_SQ, Flux) output characteristic, I wondering what DC and AC impedance have I to considered ?
- First I assume a DC impedance R_DC (operating point) regarding the DC biasing of about an half the shunt resistance. However, this DC operating point evolve with plux leading with non-constant R_DC in large signals.
- Then, have I to suppose dynamic output impedance Z_AC = dV_SQ/dI_SQ, even I_SQ is kept constant ... and only the flux (input signal) is varying? Or have I to introduce another expression depending the d_Flux ? How can I determine fluctuation of the output dynamic impedance in case of large flux signal (load line)? Do you know references discussion "DC and AC" SQUID output impedance ?
- Last, if I want to match the output impedance, load impedance compromises control of the current biasing: The biasing I_0 is not any more a current biasing (Norton impedance of the biasing in // with matched readout is same order of magnitude as the SQUID impedance. So, SQUID curent is not any more kept constant). Know you a reference discussion biasing in case of impedance SQUID output matching?
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