Operating Margin Measurements for an AC Josephson Voltage Standard

For a number of years, NIST has been developing a Josephson arbitrary waveform synthesizer as an ac Josephson Voltage Standard (ACJVS). The effort has primarily focused on increasing the output voltage to practical levels. Recent advances in circuit design and superconducting integrated circuit fabrication have enabled us for the first time to demonstrate waveforms with a 242 mV peak voltage. This larger output voltage now allows us to perform practical metrology measurements with rms amplitudes up to 170 mV. The new system can generate a variety of precision voltage waveforms, including ac sinewaves as well as dc voltages so that the system can be used as a quantum-based voltage source for ac metrology. In this paper, we present experimental measurements of 2.7 kHz and 3.3 kHz waveforms synthesized by the ACJVS measured with both a FFT (fast Fourier transform) spectrum analyzer and an ac/dc transfer standard. This work demonstrates the feasibility of a practical ac Josephson voltage standard based upon a quantum voltage source that delivers precisely calculable ac and dc rms voltages.