A double junction ring oscillator based on shunted, stacked junctions

We present the design of a double junction ring oscillator, along with initial rf measurements. The ring oscillator design includes the usage of two shunted, stacked junction devices ("Stacktrons") as active switching nodes in the ring. The rf detection circuitry was designed to accommodate both a detector junction for measuring Shapiro steps and a finline antenna for broadband rf. As a motivation for our study, the double junction ring oscillator allows the probe of the multiple flux quantum (MFQ) state, which is a distinct, transient dynamical state resulting from the synchronous switching of nodal junctions in the circuit. Such a state has several possible applications. We quantify the existence of the MFQ state in the ring circuit configuration with numerical simulations, including circuit margins and yield. Finally, we provide a detailed explanation of the coupling circuitry between the ring oscillator and rf detection circuitry.