Alain Rufenacht

Precision Differential Sampling Measurements of Low-Frequency Synthesized Sine Waves With an AC Programmable Josephson Voltage Standard

We have developed a precision technique to measure sine-wave sources with the use of a quantum-accurate AC programmable Josephson voltage standard. This paper describes a differential method that uses an integrating sampling voltmeter to precisely determine the amplitude and phase of high-purity and low-frequency (a few hundred hertz or less) sine-wave voltages. We have performed a variety of measurements to evaluate this differential technique. After averaging, the uncertainty obtained in the determination of the amplitude of a 1.2 V sine wave at 50 Hz is 0.3 muV/V (type A). Finally, we propose a dual-waveform approach for measuring two precision sine waves with the use of a single Josephson system. Currently, the National Institute of Standards and Technology (NIST) is developing a new calibration system for electrical power measurements based on this technique.

Systematic error analysis of stepwise approximated AC waveforms generated by a Programmable Josephson Voltage Standard

We have measured stepwise-approximated sine waves generated by a programmable Josephson voltage standard (PJVS) with several different output configurations. These data are analyzed to characterize the dominant error mechanisms for RMS applications, such as AC-DC difference measurements of thermal voltage converters (TVCs). We present detailed explanations of the fundamental causes and consequences of systematic errors that arise from transitions and consider the overall uncertainties for PJVS ac metrology using this synthesis method. We show that timing-related errors are sufficient to make this waveform synthesis approach impractical for RMS audio-frequency applications. The implications of providing the load current required by devices of low input impedance, such as TVCs, are also discussed.

Error and Transient Analysis of Stepwise-Approximated Sine Waves Generated by Programmable Josephson Voltage Standards

We are developing a quantum-based 60 Hz power standard that exploits the precision sinusoidal reference voltages synthesized by a programmable Josephson voltage standard (PJVS). PJVS systems use series arrays of Josephson junctions as a multibit digital-to-analog converter to produce accurate quantum-based dc voltages. Using stepwise-approximation synthesis, the system can also generate arbitrary ac waveforms [i.e., an ac programmable Josephson voltage standard (ACPJVS)] and, in this application, produces sine waves with calculable root mean square (rms) voltage and spectral content. The primary drawback to this ACPJVS synthesis technique is the uncertainty that results from switching between the discrete voltages due to finite rise times and transient signals. In this paper, we present measurements and simulations that elucidate some of the error sources that are intrinsic to the ACPJVS when used for rms measurements. In particular, we consider sine waves synthesized at frequencies up to the audio range, where the effect of these errors is more easily measured because the fixed transition time becomes a greater fraction of the time in each quantized voltage state. Our goal for the power standard is to reduce all error sources and uncertainty contributions from the PJVS-synthesized waveforms at 60 Hz to a few parts in 107 so that the overall uncertainty in an ac power standard will be a few parts in 106.

NIST 10 V Programmable Josephson Voltage Standard System

The National Institute of Standards and Technology has developed and implemented a new programmable Josephson voltage standard (PJVS) that operates at 10 V. This next-generation system is optimized for both dc metrology and stepwise-approximated ac voltage measurements for frequencies up to a few hundreds of hertz. The nonhysteretic Josephson junctions produce intrinsically stable voltages and are designed to operate in the 18-20 GHz frequency range. The most recent 10 V PJVS circuits have total output current ranges greater than 1 mA.

Precision sampling measurements using ac programmable Josephson voltage standards.

We have performed a variety of precision measurements by comparing ac and dc waveforms generated by two independent ac programmable Josephson voltage standard (ACPJVS) systems. The objective of these experiments was to demonstrate the effectiveness of using a sampling digital voltmeter to measure small differences between Josephson waveforms for frequencies up to 3.6 kHz. The low uncertainties that we obtained confirm the feasibility of using this differential sampling method for high accuracy comparisons between ACPJVS waveforms and signals from other sources.

Josephson-Voltage-Standard-Locked Sine Wave Synthesizer: Margin Evaluation and Stability

This paper describes a Josephson-voltage-standard-locked synthesizer where a commercial digital-to-analog converter is used as a sine wave generator. The output amplitude of the generator is controlled by the calculable fundamental of the stepwise waveform generated by a SINIS Josephson junction array. Such a system combines the versatility of a commercial source with the stability and accuracy of the Josephson standard. By discarding the measurements performed during the transients, broad voltage steps of 1.7 mA were obtained up to frequencies of 500 Hz.

Characterization of Metrological Grade Analog-to-Digital Converters Using a Programmable Josephson Voltage Standard

A test bench has been developed for systematic characterization of high-resolution analog-to-digital converters. The reference signal is generated by a programable Josephson voltage standard. Three 24-bit digitizers have been characterized. Noise performance has been measured at direct current using the Allan deviation, whereas integral nonlinearity has been measured with quasi-dynamic stepwise triangular waveforms at frequencies between 0.5 Hz and 1 kHz. None of the digitizers outperforms all others for each tested characteristics. Therefore, such a systematic characterization provides the overview needed to identify the most suitable digitizer for a given application.

High precision comparison between SNS and SIS Josephson voltage standards

Recently, a new Josephson voltage standard based on a 1 V programmable chip provided by the National Institute of Standards and Technology (NIST) was implemented at the Swiss Federal Office of Metrology (OFMET). A comparison with a conventional Josephson voltage standard showed an agreement of (1.4/spl plusmn/3.4)/spl times/10/sup -10/ at 1 V. This result demonstrates the new system is functioning properly and can be used in various types of measurements. In particular, it will be one of the key components of the Watt balance experiment (1999) at OFMET.

Thermal-Transfer Standard Validation of the Josephson-Voltage-Standard-Locked Sine-Wave Synthesizer

This paper describes a Josephson-voltage-standard-locked synthesizer where a calibrator is used as a sine-wave generator, output whose is controlled by the calculable fundamental of the stepwise sinusoidal wave generated by a programmable Josephson junction array. Such a system combines the versatility of a calibrator with the stability and the accuracy of the Josephson voltage standard. The validity of this method was confirmed with the ac-dc difference measurements of a calibrated thermal-transfer standard. The synthesizer uncertainty inferred is below 1.2 μV/V for waveform frequencies up to 1 kHz and root-mean-square amplitudes ranging from 100 mV to 1 V.

High precision comparison between a programmable and a pulse-driven Josephson voltage standard

Over the last 15 years, research in ac Josephson voltage metrology has focused on two fundamentally different systems: the programmable and the pulse-driven Josephson voltage standards (JVSs). This paper reports the first high precision comparison between the two types of JVS. The METAS programmable voltage standard was moved from Switzerland to the Netherlands to be compared with the Dutch pulse-driven system during four days in November 2010. After a careful investigation of the systematic sources of errors, the comparison was made at a frequency of 500 Hz and an rms amplitude of 104 mV. At that level, the voltage difference measured between the fundamental frequency components of the two standards was −0.18 ± 0.26 µV V−1 (k = 2), showing an excellent agreement between the two systems.