An AC Josephson voltage standard for AC-DC transfer-standard measurements

In order to improve the National Institute of Standards and Technology (NIST) low-voltage calibration service for thermal-voltage converters, we have constructed an ac-Josephson-voltage-standard (ACJVS) system that can synthesize accurate rms voltages of up to 100 mV. Using this system, we synthesized dc voltages and audio-frequency sine waves in order to measure ac-dc differences on the 22 mV and 220 mV ranges of a commercial thermal transfer standard. By modifying the output resistance of the low-pass-filtered transmission line, we were able to extend our measurement frequency from a few kilohertz up to 100 kHz. Our ACJVS measurements agree with the uncertainty budget of ac-dc difference calibrations made of this transfer standard by use of conventional techniques. We also show the progress toward extending the output to 200 mV using new Josephson circuits.