Method for ensuring accurate AC waveforms with programmable Josephson voltage standards

Abstract

The amplitudes of stepwise-approximated sine waves generated by programmable Josephson voltage standards (PJVS) are not intrinsically accurate because the transitions between the quantized voltages depend on numerous conditions. We have developed a method that ensures that the total rms output voltage of arbitrary ac waveforms synthesized by the PJVS are accurate and referenced to the quantized Josephson voltages. This is accomplished by digitizing the entire output waveform, utilizing the quantum voltages to correct digitizer gain, noise, and nonlinearity, and then applying our understanding of the interplay between measurement bandwidth, risetime, and harmonic content to precisely tune the bias parameters. Our goal is to develop an AC standard source for voltage metrology that can directly synthesize voltages with the accuracy expected of a quantum-based standard without the use of a thermal voltage converter. *

Differential Sampling Measurement of a 7 V RMS Sine Wave With a Programmable Josephson Voltage Standard

“…1). Other measurement methods that directly apply synthesized waveforms from the PJVS [12]- [14] are limited to applications with high-impedance loads, and the stepwiseapproximated waveforms contain harmonics that significantly contribute to the total RMS voltage [15]. The advantage of the differential sampling method is that the output of the sine-wave source can be used directly to drive low-impedance loads [16].…”

Direct comparison of a pulse-driven Josephson arbitrary waveform synthesizer and a programmable Josephson voltage standard at 1 volt

“…The duration of each PJVS level is set to 125 µs (N = 80 levels/period and 100 Hz). We acquire 100 periods of the differential voltage with a sampling frequency of 10 MHz, average, and apply the previously mentioned gain correction for the digitizer [5]. The first 30 µs and last 10 µs of each PJVS level are discarded to remove the PJVS transients and the oscillations due to the finite impulse response filter of the digitizer.…”