PLL-Based Readout Circuit for SiC-MOS Capacitor Hydrogen Sensors in Industrial Environments.

Andrei Enache,Mihaela Pantazica,Gheorghe Pristavu,Florin Draghici,Gheorghe Brezeanu,Florin Mitu,Razvan Pascu

doi:10.3390/s22041462

Abstract

For proper operation in real industrial conditions, gas sensors require readout circuits which offer accuracy, noise robustness, energy efficiency and portability. We present an innovative, dedicated readout circuit with a phase locked loop (PLL) architecture for SiC-MOS capacitor sensors. A hydrogen detection system using this circuit is designed, simulated, implemented and tested. The PLL converts the MOS nonlinear small-signal capacitance (affected by hydrogen) into an output voltage proportional to the detected gas concentration. Thus, the MOS sensing element is part of the PLL’s voltage-controlled oscillator. This block effectively provides a small AC signal (around 70 mV at 1 MHz) for the sensor and acquires its response. The correct operation of the proposed readout circuit is validated by simulations and experiments. Hydrogen measurements are performed for concentrations up to 1600 ppm. The PLL output exhibited voltage variations close to those discernable from experimental C-V curves, acquired with a semiconductor characterization system, for all investigated MOS sensor samples.

Highlights

The applications of gas sensors have broadened considerably over time, extending from monitoring concentrations under the olfactory human limit to detecting the presence of dangerous compounds and ensuring work safety
Volatile organic compounds (VOCs), H2 S and NO2 are among the substances of interest when checking whether an environment is habitable or work suitable
This paper proposes a portable hydrogen detection system with alternate readout circuit architecture

Summary

Introduction

The applications of gas sensors have broadened considerably over time, extending from monitoring concentrations under the olfactory human limit to detecting the presence of dangerous compounds and ensuring work safety. In the search for clean and renewable energy, hydrogen (H2 ) has emerged as one of the leading candidates [2,3,4,5,6,7,8,9,10] It is a highly explosive gas, if its concentration in air exceeds 4.65% [11,12]. The need for high performance sensors (and associated readout circuits) to detect H2 in multiple applications is increasing rapidly [13] Oftentimes, these applications are in harsh environments, such as the aerospace domain [11,14,15] the industrial sector [16,17] or, more recently, the automotive field for hydrogen powered vehicles [18,19]

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Conclusion