LINEWIDTH MEASUREMENTS AND PHASE-LOCKING OF JOSEPHSON OSCILLATORS USING RSFQ CIRCUITS

We present a technique far linewidth measurement and phase-locking of Josephson oscillators using digital rapid single-flux-quantum (RSFQ) c ircuits, The oscillator consists of a resistively shunted 6 mu m x 6 m u m Nb/AlOx/Nb Josephson tunnel junction that is integrated with RSFQ input and output circuits. A cascade of RSFQ T flip-flops is used to d irectly monitor the output of the Josephson oscillator, Spectral chara cteristics have been measured directly far oscillator frequencies rang ing from 10-50 GHz, The linewidth can be reduced by over 100 times by phase-locking the oscillator to an RSFQ pulse train generated by an ex ternal sinusoidal signal, These Josephson oscillators can be used as o n-chip stable high frequency clocks for RSFQ circuits.