Josephson Waveform Synthesizer Research Articles

Technique for the calibration of thermal voltage converters using a Josephson waveform synthesizer and a transconductance amplifier

This paper describes a simple and effective technique for calibrating thermal converters for an ac–dc voltage transfer difference using a Josephson waveform synthesizer and a transconductance amplifier. Preliminary measurements and uncertainty analysis confirm the possibility of achieving systematic uncertainties below 0.1 µV V−1 at frequencies up to 1 kHz.

Precision AC–DC Transfer Measurements With a Josephson Waveform Synthesizer and a Buffer Amplifier

Measurements of the ac-dc difference of a thermal converter have been performed using a Josephson waveform synthesizer and a precision buffer amplifier at frequencies from 10 Hz to 4 kHz, showing agreement with conventional standards of better than 1 μV/V up to 1 kHz. In addition, a method of finding the operating parameters of the programmable Josephson array that corresponds to minimal uncertainty is discussed.

The Josephson-Effect-Based Primary AC Power Standard at the PTB: Progress Report

This paper reports the incorporation of a Josephson waveform synthesizer (JWS) into the primary standard for AC electrical power at the Physikalisch-Technische Bundesanstalt (PTB). The increase to 10 V of the amplitude delivered by the JWS has allowed matching of the levels of the signals measured to determine the active, reactive, and apparent power-at the 120-V and 5-A level, which is also measured by the device under test. The inherent noise- and drift-free voltages delivered by the JWS allow calibration of the core sampling voltmeter of the PTB primary power standard with an uncertainty of 0.4 muV/V(k = 1) in 100 signal periods and as part of the measuring sequence.

Design and Characterization of a Sampling System Based on $\Sigma$–$\Delta$ Analog-to-Digital Converters for Electrical Metrology

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper describes a sampling system designed using a commercial sigma–delta analog-to-digital converter (<formula formulatype="inline"><tex Notation="TeX">$\Sigma$</tex></formula>–<formula formulatype="inline"><tex Notation="TeX">$ \Delta$</tex></formula> ADC). In addition to characterization measurements using a conventional high-quality signal generator, a Josephson waveform synthesizer that provides ultimately noise- and drift-free voltages was used. To evaluate the suitability of this sampling system as part of a transfer power standard, additional comparisons of the root-mean-square (RMS) values measured were performed against a thermal converter and the primary power sampling standard at the Physikalisch-Technische Bundesanstalt, Braunschweig, Germany. Initial analysis of the measurement data shows an effective resolution in the range of 18–19 bits at an equivalent sampling rate of 64 kHz. The integral nonlinearity error of the system was measured to be within <formula formulatype="inline"><tex Notation="TeX">$\pm 7\ \mu \hbox{V/V}$</tex></formula> or one least significant bit at this resolution. </para>

Primary AC Power Standard Based on Programmable Josephson Junction Arrays

Josephson series arrays have been operated as digital-to-analog converters with fundamental accuracy to generate precision waveforms with accuracies better than one part in 107 at power frequencies. These waveforms have been used in the past to calibrate the sampling voltmeter in the primary standard for electrical power at the Physikalisch-Technische Bundesanstalt (PTB). The present contribution reports the integration of such a Josephson waveform synthesizer into the PTB primary power standard in order to continuously calibrate the sampling voltmeter and thus reduce the uncertainty for the measurement of active, reactive, and apparent power at the 120-V and 5-A levels

Numerical simulations of Josephson waveform synthesizer driven by current pulses without in-band components

The pulse-driven Josephson junction array is a promising candidate for an accurate waveform synthesizer. The accuracy of the synthesized waveform is chiefly limited by the in-band frequency components of the driving current because they couple to the output signal through parasitic circuit elements and are difficult to filter out. In this study, we propose a more accurate waveform synthesis method, in which the array is driven by current pulses which have the same waveform as the impulse response of the ideal bandpass filter. Simulations have shown that the current amplitude of the constant-voltage step of a junction driven by the filtered pulses exceeds 70% of the Josephson critical current in a wide range of output signals. Synthesis of a sine wave using this method was also demonstrated by simulation.

AC coupling technique for Josephson waveform synthesis

We demonstrate a new bias technique that uses low-pass and high-pass filters to separate the current paths of the sampling and signal frequencies in a Josephson waveform synthesizer. This technique enables the output voltage of the array to be directly grounded by removing the low-frequency common mode signal that previously prevented direct measurement of the array voltage with low-impedance instruments. We directly measure the harmonic spectra of 1 kHz and 50 kHz synthesized sine waves. We also use a thermal transfer standard to compare the rms voltages of synthesized sine waves at frequencies from 1 kHz to 50 kHz. Finally, we describe a new circuit that should enable a significant increase in output voltage by allowing several distributed arrays to be biased in parallel at high frequency, while combining their low frequency output voltages in series.