Ultra-low-power interface circuits for gas sensors with a high resistance range
(2025)
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- Authors
- Supervisors
- Flandre, Denis
- Abstract
- As technology has developed, an ever-increasing number of gases are being used in industrial processes, transportation and household applications. Unlike mainstream gas sensing technologies, novel chemiresistive gas sensors allow for the integration of tenths of devices in the same package with low power consumption and submillimetre size where each sensing layer is engineered to react to a different gas. The optimization of the sensor’s readout circuit is essential to achieve low energy measurements and long-life in battery-powered devices. In this dissertation we study the following questions: What are the electrical characteristics of chemiresistive gas sensors of relevance to electronic interfaces? What ROIC architecture is most suitable for a multi-sensor system? What are the implications in terms of power consumption and SNR for a relaxation-oscillator-based ROICs interfacing chemiresistive gas sensors? Firstly, we show that chemiresistive gas sensors have and non-ohmic resistance and depending on the sensor’s characteristics, the resistance can be very high, above 100 MΩ. In terms of noise, the power spectral density reassembles that of flicker noise but with a dependence on the sensor’s bias voltage. We propose a three-parameter mathematical model of the noise in the frequency domain. Secondly, we analysed several readout circuits architectures and conclude that relaxation-oscillator-based circuits can achieve simultaneously low power and a very high input range while maintaining an acceptable signal-to-noise ratio for chemiresistive gas sensors. Three readout circuits where fabricated and characterized, being able to measure sensors up to 1 GΩ. Thirdly, we show that the energy consumed per oscillation in relaxation-oscillators-based readout circuits is proportional to sensor’s resistance. To address this issue, we present two novel adaptive biasing techniques for comparators, that can reduce the total power consumption of the readout up to 94 % when compared to standard comparators. Lastly, we evaluate three ways of digitizing the frequency of the oscillator. We found it is best to use dedicated digital devices, like modern microcontrollers, instead of performing digitally-intensive operations inside analog integrated circuits made in 180 nm CMOS processes.
- Affiliations
Citations
Puyol Troisi, R. (2025). Ultra-low-power interface circuits for gas sensors with a high resistance range. https://hdl.handle.net/2078.5/246537