Novel, All-Digital Phase Measurement System for Time Scales

Abstract : A novel, all-digital phase measurement system to be utilized as part of the NIST time scale at NIST in Boulder, CO is presented. The system is used to compare output signals from different commercial atomic frequency standards; the phase differences between these signals will be fed to the algorithm used to generate the NIST time scale. Preliminary results from common-clock measurements show a time deviation sigma(x)(tau) < 6x10(exp-13) s for measurement times up to 2000 s and below 1 ps for measurement times up to 10,000 s. Within these measurement times, and up to 250,000 s (approximately 3 days), the performance of the system is comparable to the measurement system presently integrated in UTC (NIST). A direct comparison of different clock measurements as performed by the system described in this paper and by the one that is part of UTC (NIST) is also presented as a mean of validation of the newly developed measurement system.