ANALOG-TO-DIGITAL CONVERSION WITH A SQUID - CONDITIONS FOR A COUNTABLE PULSE TRAIN

A superconducting loop containing a Josephson junction develops voltage pulses when it admits and expels magnetic flux quanta, and thus may be used as an A/D converter. We here develop and discuss several conditions which must be satisfied for the generation by the SQUID of an unambiguously countable pulse train, from which the analog signal can be faithfully reconstructed. These conditions can be satisfied over a broad range of realizable values of inductance and resistance. The capacitance, however, must be carefully controlled. The results of simulations are also presented, illustrating the various ways in which the pulse trains are affected.