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Waveform metrology based on spectrally pure Josephson voltages

Short Name: QuADC, Project Number: 15SIB04
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An accurate, stable and rapid AC voltage measurement system for industrial end-use

The European Commission’s ‘Digital Single Market Strategy’ aims at creating the right conditions for digital networks and services to flourish, maximising the growth of the digital economy. A core requirement of many digital systems is converting analogue electrical signals to digital (analogue to digital conversion, ADC). Modern technologies, like precision integrated circuits and measurement equipment, require increasingly rapid ADC sampling rates and traceability to the volt, the SI unit of electrical potential energy.

Before this project, direct current (DC) measurements could be traced to the volt but alternating current (AC) measurements could not. Traceability for AC voltages was provided by thermal transfer devices, which equate the electrical heating power of a DC current and an AC current. These couldn’t provide a direct link to the SI volt, due to uncertainty in the traceability chain, and couldn’t give information on the harmonic content of AC voltage, so were unsuitable for some ADC instrument calibrations. Furthermore, calibrations had to be performed at many frequencies and voltages which was time-consuming, restricting uptake by industry.


Following the  EMRP project  Q-WAVE, this project developed a new quantum-based voltage standard which generates spectrally pure arbitrary waveforms with quantised output voltages. The new standard demonstrates high transportation stability and, unlike thermal transfer standards, can make measurements in minutes with 100x lower uncertainty.

The standard uses a ‘state of the art’ Josephson Arbitrary Waveform Synthesiser (JAWS). When arbitrary current pulses are applied, using a new optical pulse pattern generator developed in the project, it generates quantized voltage-time pulses, used to construct voltage waveforms directly traceable to the SI. The standard has a DC voltage range of up to 100 kHz, due to the development of improved voltage dividers, and an optimised low temperature photodiode mounting procedure has made it more reliable and robust to thermal cycling. ‘Impedance matching’ techniques were also applied to cancel out loading effects caused by cables and decrease discrepancies between the applied and calculated voltages.

The voltage divider was used in the EMPIR project  DIG-AC which addressed ways to advance the European capability for digital evaluation of dynamic AC voltage and current by utilising quantum standards and publicly available measurement systems.


The new measurement instrumentation will allow a range of industrial end-users to develop previously unachievable processes and products that rely on fast ADC and provide support to smart electricity grids. 


Project website
Other Participants
Applicos B.V. (Netherlands)
esz AG calibration & metrology (Germany)
Instituto Nacional de Tecnología Industrial (Argentina)
Signal Conversion Ltd (United Kingdom)
Universitetet i Sørøst-Norge (Norway)


SI Broader Scope
2016 - 2019