Effect of Additional Reference Current in a Reference Junction-Double Relaxation Oscillation SQUID (RJ-DROS).

A double relaxation oscillation SQUID with a reference junction (RJ-DROS) already has a fixed reference current, so that it holds a fixed flux-to-voltage characteristics when fabricated. When an additional current flows through the reference junction but not through the signal junction in the RJ-DROS, we have obtained the variation of its characteristics. The additional reference current has an effect on reducing the fixed reference current, which results in changing averaged relaxation voltage and transfer coefficient. In particular, while the critical current of the signal SQUID exceeds the reference current, the averaged relaxation voltage at the reference junction is enlarged by the added bias current combined with an additional current and an initial bias current. Therefore the additional reference current can provide the RJ-DROS with variable modulation depth and width within the operating range. Although the characteristics of RJ-DROSs are fixed differently each to each when they are fabricated, the additional current can adjust their characteristics to the same one, which is useful for controlling DROSs in a multichannel DROS system. However, an input-bias current in the preamplifier detecting the outputs at the reference junction, acts as an additional current, and then makes the reference current shift from the optimum current or deviate from the operating range, the input-bias current needs to be regulated within the operating range. [ABSTRACT FROM AUTHOR]