Automated impedance metrology extending the quantum toolbox for electricity

Short Name: AIM QuTE, Project Number: SIB53
Power resistors

Impedance measurements for electrical components: Simple, reliable and cost-effective impedance measurements 

Precise measurement of impedance – the resistance a circuit presents to an AC current – is vital to modern electronics. Uses include providing touch responses from smartphone screens, accurate measurements in radiation dosimeters and fuel gauges, the validation of nanoscale components and the analysis of energy loss in transmission lines.


Impedance values are defined using the Quantum Hall Effect, which can be scaled-up with pre-set transformers to create a range of impedance standards. These are all at fixed ratios, e.g. 1:2, 1:5, governed by the number of windings in the transformers used.


As electronics gain sophistication, increased measurement precision is needed. Users want calibrations for their impedance measurement instruments at intermediate values rather than at the fixed steps that are currently available, with robust links to SI units. Josephson bridges, superconducting devices that can compare two impedances, have the potential to address this issue.


This project developed and validated Josephson and digital bridges as a simpler method for calibrating impedance standards for a wider range of values.


The project:


• Developed and validated a software driven Josephson bridge that can automatically set impedance ratios, allowing multiple impedance ratios to be achieved with a single instrument


• Developed electrical signal sources for verifying bridge performance to achieve higher levels of precision than previously possible based on modelling to determine and reduce errors


• Developed a highly accurate fully-digital and automated voltage ratio bridge, with an adjustment time of less than one minute that both simplifies impedance ratio comparisons and can replace the current reliance on fixed impedance transformers


• Compared four impedance bridges using specially developed impedance standards with intermediate phase angles, demonstrating consistency of output across different phase angles, but also highlighting further considerations for assessing bridge performance.


This project developed new impedance measurement capabilities using automated bridges. It simplified impedance measurement instrument calibrations across multiple fixed ratios, as well as allowing the use of intermediate ratios for the first time, without sacrificing accuracy. In the longer term this will speed up and simplify previously complex instrument calibrations. Project advances also now provide calibrations at lower capacitance levels than were previously possible, which is important for new nanotechnologies and touch sensitive devices that respond to very tiny impedance/capacitance changes. Commercial interest in the project’s new impedance standards has been expressed by a semiconductor manufacturer that needs individual standards for low value capacitances. The improved calibrations resulting from this project will allow more accurate impedance measurement and testing, supporting innovation in the next generation of electronics and sensors.


For more information, please contact the EURAMET Management Support Unit

Phone: +44 20 8943 6666


Project website