A Low-Power, Wireless, Capacitive Sensing Frontend Based on a Self-Oscillating Inductive Link

Schormans, Matthew; Valente, V.; Demosthenous, Andreas

doi:10.1109/TCSI.2018.2835148

A Low-Power, Wireless, Capacitive Sensing Frontend Based on a Self-Oscillating Inductive Link

Journal article (2018)

Authors

Matthew Schormans University College London

V. Valente University College London, Bio-Electronics -

Andreas Demosthenous University College London

Research Group

Bio-Electronics () (TU Delft)

DOI: https://doi.org/10.1109/TCSI.2018.2835148

Sensors Monitoring Impedance Wireless sensor networks Wireless communication Capacitance Capacitive sensing Humidity sensing Inductive link Resonant frequency Wireless sensing.

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Published Date

2018

Language

English

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Faculty

Electrical Engineering, Mathematics and Computer Science

Department

Microelectronics

Research Group

Bio-Electronics

Abstract

Wireless sensing systems are becoming popular in a range of applications, particularly in the case of biomedical circuits and food monitoring systems. A typical wireless sensing system, however, may require considerable complexity to perform the necessary analog to digital conversion and subsequent wireless transmission. Alternatively, in the case of inductive link based systems, large, manually operated impedance analyzers are required. Based on a detailed analysis of the link impedance, this paper proposes a simple method for wireless capacitive sensing through an inductive link that uses a self-oscillator and a frequency counter. The method enables changes in capacitance to be sensed and wirelessly transmitted simultaneously. In order to test the effectiveness of the method, a self-oscillating circuit was designed and fabricated in 0.18 μm CMOS, and combined with an on-chip humidity sensing capacitor. The system was tested in a humidity chamber across a range of 20-90%rh. Measured results from the system demonstrate that capacitive changes as small as 28 fF, translating to <2%rh, can be resolved, with a power consumption of 1.44 mW.

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