Josephson voltage standard-a review

The unique ability of a Josephson junction to convert a microwave frequency f into a voltage Nhf/2e with high accuracy and the adoption of this phenomenon as the basis for the SI Volt Realization have created a market for Josephson voltage standards that is unassailable from any other technology. This paper reviews the development of Josephson voltage standards including the junction and array design, the microwave circuit, and the system integration. With the dc Josephson standard largely transferred to the commercial sector, NIST is developing a new class of devices in which the output voltage can be rapidly programmed either by digitally selecting the quantum number N or by driving the Josephson array with a variable frequency pulse train. These new devices will make possible fast, high-accuracy characterizations of A/D and D/A converters and the synthesis of ac waveforms.