NEW TECHNIQUE FOR A HIGHER VOLTAGE AC JOSEPHSON STANDARD.

Achieving practical output voltages is one of the greatest challenges for the ac Josephson voltage standard, also known as the Josephson arbitrary waveform synthesizer. Researchers recently have demonstrated an ac coupling technique that increases the useful output voltage for metrology measurements. Metrology applications require direct coupling of the array voltage to the calibration instrument with no common mode voltage. 5.4 mV was the previous highest peak output voltage able to be used for metrology calibrations. The voltage was low because only small arrays of 250 junctions could be uniformly biased without a common mode voltage. In the ac coupled technique, NIST researchers have effectively removed the common mode signal by dividing the low and high frequency bias components and applying them to the array through different circuits. With this technique, arrays of 4096 junctions have been used to achieve more than a 10-fold increase in output voltage (64 m V peak) for a single array with no degradation in operating margins. This technique also has the potential for significantly higher output voltage by enabling multiple arrays to be connected in series. The first ac-dc voltage comparisons using this technique will be performed in the next few weeks.