Effect of Voltage Bias on the dc SQUID Characteristics

The dynamics of the dc SQUID, when voltage biased through an inductor, is computed by numerical simulation and by perturbative analytical calculation. We find that the dynamic resistance decreases from its current-biased value at low bias voltages, where the inductive series reactance no longer separates the Josephson voltage oscillation from the bias source. The flux-to-current conversion ratio, however, remains almost unaffected. This effect is sometimes important in setups, where a second SQUID is used as a readout amplifier.