A Josephson Impedance Bridge Based on Programmable Josephson Voltage Standards

The Josephson impedance bridge at the Physikalisch-Technische Bundesanstalt has progressed from its first implementation to a semiautomated calibration tool able to perform a frequency sweep from 25 Hz to 10 kHz in less than 2 h. An analysis of systematic errors is presented, which focuses on the measurement of capacitance standards. We identified the transients as a major source of uncertainty and show a number of solutions. Additionally, extending the bridge to a four terminal system for lower uncertainties at lower value impedances has been tested. Finally a detailed uncertainty budget is presented, showing uncertainties from 0.9 x 10
^-8
to 81.1 x 10
^-8
for 1:1 and 1:10 ratio measurements with 10 and 100 pF capacitors.