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By employing an array of 620 high-Tc Josephson junctions, we have achieved a maximum quantum output voltage with approximate value of 0.1 V at a temperature of 79.2 K and a frequency of 77.465 GHz. We also demonstrate that steps on the current-voltage characteristic of an array of bicrystal junctions at voltages of 70 mV were flat over the current range of 150 muA with a relative uncertainty of 0...
A waveform synthesizer adopting a programmable Josephson voltage standard has been developed, which can produce stepwise sinusoidal waveforms with few hundred quantum voltage levels. For synthesis of waveforms, individual cells on the Josephson array chip were promptly biased using a 7-channel current source with 14-bit resolution. As an application, the synthesizer was utilized as a fast-reversed...
NIST is designing a 10 V Programmable Josephson Voltage Standard (PJVS) system with an improved microwave design and arrays of stacked NbxSi1-x-barrier Josephson junctions. For this new design a "ground-up" approach was used that takes into account all system issues in order to produce a robust 10 V system. By improving the uniformity of the microwave drive along the length of each array,...
An ac-dc transfer measurement system based on a programmable Josephson voltage standard (PJVS) is being developed. Performance of the standard with dc and synthesized ac bias has been characterised. The first ac-dc transfer measurement results indicate agreement with conventional standards of the order of 1 muV/V at frequencies up to 40 Hz.
Nb/Al-AlOx/Nb Josephson junctions of few micrometers size, derived by the basic hysteretic SIS process, have shown stable overdamped current voltage, I-V, characteristic with Ic of 1-10 mA and Vc of 100-600 muV at 4.2 K. The moderate dependence on temperature of these parameters has allowed to use them at temperatures above 4.2 K, near the Nb transition temperature, measuring quantized voltage steps...
This paper describes an DC voltage calibration system which is improved to be more accurate and more easy to operate. It is based on 10 V Josephson array, and uses a fully automated system consisting of switches setup well designed for accurate measurement. An overall standard uncertainty is estimated less than 5 nV(1sigma) at 10 V level.
We present a new record output voltage of 275 mV rms, which is a 25 % improvement over the maximum achieved with previous ac Josephson voltage standard circuits. We demonstrate operating margins for these circuits and use them to measure the harmonic distortion of a commercial digitizer. Having exceeded the threshold of 125 mV rms for a single array of Josephson junctions, we propose an eight-array...
The AC quantum voltmeter, an instrument for measuring AC waveforms by comparing them to a Josephson waveform, has been enhanced. Two different improvements to the signal-to-noise ratio are presented. The signal amplitude has been significantly increased by using 10-V Josephson arrays. The noise contribution has been reduced by adding a preamplifier at the input of the sampling null detector.
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