Measurement of jitter in a long Josephson junction soliton oscillator clock source
Stability of Josephson junction clock sources can be a limiting factor in the operation of RSFQ digital and mixed signal circuits. We have developed techniques for the characterization of the short-term stability, i.e., the jitter, of Josephson junction clock sources, and in this paper we present measurements of the jitter for a long Josephson junction soliton oscillator clock. The output frequency of the soliton oscillator was prescaled by using a chain of T flip-flops and using a current bias feedback the oscillator was phase locked to a stable room temperature RP source. Phase noise spectra of the clock signal were measured at the successive stages of the T flip-flop chain and interpreted to infer the cycle-to-cycle jitter of the soliton oscillator. The jitter at the output of the soliton oscillator was measured to be 60 fs at a frequency of 26 GHz, or 0.16% of the period of the clock.