Ring oscillator experiment using a huffle circuit

A ring oscillator circuit composed of Josephson junction devices has been designed and tested for the first time. Nine huffle circuits, each of which includes two Josephson junctions of an in-line gate type, are combined to form an inverter ring. The ring oscillator has produced oscillations with 1.8- to 8.2-ns periods using DC power sources. Inverter and flip-flop logic operations are also observed with the single huffle circuit. The operating margins were investigated and found to be reasonable as a result of comparing experimental threshold curves and a theoretical prediction.