Design and simulation of a fast Josephson junction on-chip gated clock for frequency and time analysis

As the sophistication and speed of digital communication systems increase, there is a corresponding demand for more sophisticated and faster measurement instruments. One such instrument on the market is the HP 5371A frequency and time interval analyzer (FTIA). This instrument is analogous to a conventional oscilloscope. Whereas the oscilloscope measures waveform amplitudes as a function of time, the FTIA measures phase, frequency, or timing events as function of time. These applications are useful in such areas as spread-spectrum radar, chirp filter designs, disk-head evaluation, and timing jitter analysis. The on-chip clock designed for this application uses a single Josephson junction as the clock and a resonator circuit to fix the frequency. A zero-crossing detector is used to start and stop the clock. A SFQ counter is used to count the pulses generated by the clock and a reset circuit is used to reset the clock. Extensive simulations and modeling have been done based on measured values obtained from an Nb-Al₂ O₃-Al-Nb process