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A Differential Monolithically Integrated Inductive Linear Displacement Measurement Microsystem

1
Letrika Lab d.o.o., Polje 15, Šempeter pri Gorici 5290, Slovenia
2
Laboratory of Microelectronics, Faculty of Electrical Engineering, University of Ljubljana, Tržaška 25, Ljubljana 1000, Slovenia
*
Author to whom correspondence should be addressed.
Academic Editor: Vittorio M. N. Passaro
Sensors 2016, 16(3), 384; https://doi.org/10.3390/s16030384
Received: 20 January 2016 / Revised: 10 March 2016 / Accepted: 11 March 2016 / Published: 17 March 2016
(This article belongs to the Section Physical Sensors)
An inductive linear displacement measurement microsystem realized as a monolithic Application-Specific Integrated Circuit (ASIC) is presented. The system comprises integrated microtransformers as sensing elements, and analog front-end electronics for signal processing and demodulation, both jointly fabricated in a conventional commercially available four-metal 350-nm CMOS process. The key novelty of the presented system is its full integration, straightforward fabrication, and ease of application, requiring no external light or magnetic field source. Such systems therefore have the possibility of substituting certain conventional position encoder types. The microtransformers are excited by an AC signal in MHz range. The displacement information is modulated into the AC signal by a metal grating scale placed over the microsystem, employing a differential measurement principle. Homodyne mixing is used for the demodulation of the scale displacement information, returned by the ASIC as a DC signal in two quadrature channels allowing the determination of linear position of the target scale. The microsystem design, simulations, and characterization are presented. Various system operating conditions such as frequency, phase, target scale material and distance have been experimentally evaluated. The best results have been achieved at 4 MHz, demonstrating a linear resolution of 20 µm with steel and copper scale, having respective sensitivities of 0.71 V/mm and 0.99 V/mm. View Full-Text
Keywords: inductive sensor; eddy-current sensor; displacement measurement; position measurement; analog front-end; CMOS; ASIC; microtransformer; microcoil inductive sensor; eddy-current sensor; displacement measurement; position measurement; analog front-end; CMOS; ASIC; microtransformer; microcoil
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Podhraški, M.; Trontelj, J. A Differential Monolithically Integrated Inductive Linear Displacement Measurement Microsystem. Sensors 2016, 16, 384.

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