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Delta-sigma modulation microphone sensors employing a resonant tunneling diode with a suspended microstrip resonator

Koichi Maezawa (Faculty of Engineering, University of Toyama, Toyama, Japan)
Tatsuo Ito (Faculty of Engineering, University of Toyama, Toyama, Japan)
Masayuki Mori (Faculty of Engineering, University of Toyama, Toyama, Japan)

Sensor Review

ISSN: 0260-2288

Article publication date: 21 July 2020

Issue publication date: 1 October 2020

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Abstract

Purpose

This paper aims to propose and demonstrate novel microphone sensors based on the frequency delta-sigma modulation (FDSM) technique, which replaces the conventional delta-sigma modulator in the delta-sigma analog-to digital converters. A key of the FDSM technology is to use a voltage-controlled oscillator (VCO) for converting an input analog signal to a 1-bit pulse-density modulated digital signal. High-performance sensors can be realized if the VCO is replaced by an oscillator whose oscillation frequency depends on an external physical parameter.

Design/methodology/approach

Microphone sensors are proposed based on FDSM that uses a suspended microstrip disk resonator, where the backside ground plane is replaced by a thin metal diaphragm. A resonant tunneling diode (RTD) oscillator is also used, as the performance of these sensors significantly depends on the oscillation frequency. To demonstrate the basic operation of the proposal, prototype devices were fabricated with an InGaAs/AlAs RTD.

Findings

A satisfactory noise shaping property, which is a significant nature of delta-sigma modulation, was demonstrated over three decades for the prototype device. A sound-sensing peak was also clearly observed when applying 1 kHz sound from a speaker.

Practical implications

High-performance ultrasonic microphone sensors can be realized if the sensors are fabricated by using a thin InP substrate with high-frequency oscillator design.

Originality/value

In this study, the authors proposed and experimentally demonstrated novel microphone sensors, which are promising as future ultrasonic sensors that have high dynamic range with wide bandwidth.

Keywords

Acknowledgements

The authors would like to thank Mr Kazuhiko Ueda for his help in fabricating the devices. This work was supported by JSPS KAKENHI Grant Number 18H01495, and the VLSI Design and Education Center (VDEC), the University of Tokyo in collaboration with Keysight Technologies Japan, Ltd. A part of this work was carried out under Cooperative Research Project Program of the Research Institute of Electrical Communication, Tohoku University.

Citation

Maezawa, K., Ito, T. and Mori, M. (2020), "Delta-sigma modulation microphone sensors employing a resonant tunneling diode with a suspended microstrip resonator", Sensor Review, Vol. 40 No. 5, pp. 535-542. https://doi.org/10.1108/SR-03-2020-0044

Publisher

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Emerald Publishing Limited

Copyright © 2020, Emerald Publishing Limited

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