Measurement of Leakage Current to Ground in Programmable Josephson Voltage Standards

The voltage error associated with the leakage current of programmable Josephson voltage standards (PJVS) is one of the largest contributions to the uncertainty in direct comparison of voltage standards. Due to the parallel biasing scheme of the PJVS and the resulting multiple leakage paths, the quantities “leakage resistance” and “leakage current” are not necessarily equivalent. A method to measure and model the leakage current to ground for a given PJVS output voltage is presented. By upgrading simple components of the NIST system, the leakage current to ground can be reduced from 250 pA to 50 pAat 10 V.