A Phase-Domain Readout Circuit for a CMOS-Compatible Hot-Wire CO₂ Sensor

Journal article (2018)

Authors

Z. Cai NXP Semiconductors, Electronic Instrumentation - EEMCS
Robert van Veldhoven NXP Semiconductors
H. Suy Ams AG
G. de Graaf Electronic Instrumentation - EEMCS
K.A.A. Makinwa Microelectronics
M.A.P. Pertijs Electronic Instrumentation - EEMCS
Research Group
Electronic Instrumentation (EEMCS) (TU Delft)
Copyright: © 2018 Z. Cai, Robert van Veldhoven, Hilco Suy, G. de Graaf, K.A.A. Makinwa, M.A.P. Pertijs
DOI: https://doi.org/10.1109/JSSC.2018.2866374
Delta-sigma modulator Carbon dioxide (CO?) sensor CMOS compatible Phase-domain readout Energy measurement Resistive sensor Thermal conductivity (TC)
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Published Date

2018

Language

English

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Faculty

Electrical Engineering, Mathematics and Computer Science

Department

Microelectronics

Research Group

Electronic Instrumentation

Abstract

This paper presents a readout circuit for a carbon dioxide (COࠢ) sensor that measures the CO₂-dependent thermal time constant of a hot-wire transducer. The readout circuit periodically heats up the transducer and uses a phase-domain Δ Σ modulator to digitize the phase shift of the resulting temperature transients. A single resistive transducer is used both as a heater and as a temperature sensor, thus greatly simplifying its fabrication. To extract the transducer's resistance, and hence its temperature, in the presence of large heating currents, a pair of transducers is configured as a differentially driven bridge. The transducers and the readout circuit have been implemented in a standard 0.16μm CMOS technology, with an active area of 0.3 and 3.14 mm², respectively. The sensor consumes 6.8 mW from a 1.8-V supply, of which 6.3 mW is dissipated in the transducers. A resolution of 94-ppm CO₂ is achieved in a 1.8-s measurement time, which corresponds to an energy consumption of 12 mJ per measurement, >10x less than prior CO₂ sensors in CMOS technology.