77 GHz RSFQ counter for DC Josephson voltage standard applications

Josephson primary voltage standards require a frequency-locked 77 GHz signal to perform precise frequency-to-voltage conversion. We describe the development of superconducting frequency counters used for microwave source locking in Josephson junction array primary voltage standards, and discuss design challenges and high speed test results. The counters increase the accessibility of Josephson standards by reducing the size, number of components, and cost of these systems.