Martin Šíra from CMI (Czech Metrology Insittute) visited PTB (Physikalisch-Technische Bundesanstalt) for three monts, from August to October 2016, to study application of Josephson Arbitrary Waveform System for calibration of digitizers. A special waveform have been prepared with the aim of calibrating a number of digitizer parameters at once. Parameters of the waveform were based on the properties of the JAWS system in PTB. The waveform have been generated by JAWS using three different configurations of chips to get different range of waveform amplitudes. JAWS is the only device capable of generating such a waveform with sufficient precission and stability. The waveform was sampled by selected digitizers. After an extensive data processing of sampled data several digitizer parameters have been obtained and stability and correlation factors of these parameters was estimated.
Vitor Cabral from IPQ (Instituto Português da Qualidade) realized training visit in PTB from 17 to 28 of October 2016. The system setup used for the experimental work was an “AC quantum voltmeter” as a standard to calibrate directly an ac source. The reference system was formed by a PTB Josephson array of 10 V with 16 segments which were biased by a set of 4 commercial current sources. This setup forms a Programmable Josephson Voltage Standard which allows a generation of a stepwise sine wave. The source signal under calibration was compared to the Josephson voltage by a sampling process of the differential voltage measured by a commercial ADC. The measurements were conducted in the way to exploring different parameters configuration of the setup (as the sampling rate, number of periods averaged, number of deleted points in the step transitions) in order to observe the repeatability and/or reproducibility of the results, along its work range of voltage and frequency. These experimental work allowed the acquisition of practical knowledge in several operating features of the system as the: operation of the Josephson array by the control of the bias source associated; the way to check and recognize the happening of flux trapped and the process to deal with it, by the heating of the array; the process to measure and optimize the bias current to each segment of the array, the role of the different parameters configuration to define the measurement process and theirs influence in the measurement results.
Raúl Caballero Santos from CEM (Centro Español de Metrología) visited PTB. The visit was related with the frequency response and stability of Anolog–to-Digital Converters (ADC) using the PTB Josephson Array Waveform Synthesizer (JAWS). This activity has been very successful and the preliminary data obtained are very promising. This characterization will significantly improve the AC metrological application of the ADCs.
JAWS 1 in PTB laboratory is shown on follwing picture.