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A microcontroller-based lock-in amplifier for sub-milliohm resistance measurements

Journal article
Authors Lars Bengtsson
Published in Review of Scientific Instruments
Volume 83
Issue 7
Pages Artnr 075103
ISSN 0034-6748
Publication year 2012
Published at Department of Physics (GU)
Pages Artnr 075103
Language en
Links dx.doi.org/10.1063/1.4731683
https://gup.ub.gu.se/file/133300
Keywords Microcontroller, lock-in, resistance measurment, sub-milliohm
Subject categories Electronic measurement and instrumentation, Embedded Systems

Abstract

This paper presents a novel approach to the design of a digital ohmmeter with a resolution of <60 μΩ based on a general-purpose microcontroller and a high-impedance instrumentation amplifier only. The design uses two digital I/O-pins to alternate the current through the sample resistor and combined with a proper firmware routine, the design is a lock-in detector that discriminates any signal that is out of phase/frequency with the reference signal. This makes it possible to selectively detect the μV drop across sample resistors down to 55.6 μΩ using only the current that can be supplied by the digital output pins of a microcontroller. This is achieved without the need for an external reference signal generator and does not rely on the computing processing power of a digital signal processor.

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