CMOS-Compatible Carbon Dioxide Sensors

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A phase-domain readout circuit for a CMOS-compatible thermal-conductivity-based carbon dioxide sensor

The measurement of carbon-dioxide (CO2) concentration is very important in home and building automation, e.g. to control ventilation in energy-efficient buildings. This application requires compact, low-cost sensors that can measure CO₂ concentration with a resolution of &lt;200 ppm over a 2500ppm range. Conventional optical (NDIR...

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

This paper presents a readout circuit for a carbon dioxide (CO&amp;#2082;) sensor that measures the CO&amp;#x2082;-dependent thermal time constant of a hot-wire transducer. The readout circuit periodically heats up the transducer and uses a phase-domain &amp;#x0394; &amp;#x03A3; modulator to digitize the phase shift of the resulting...

A CMOS Readout Circuit for Resistive Transducers Based on Algorithmic Resistance and Power Measurement

This paper reports a readout circuit capable of accurately measuring not only the resistance of a resistive transducer, but also the power dissipated in it, which is a critical parameter in thermal flow sensors or thermal-conductivity sensors. A front-end circuit, integrated in a standard CMOS technology, sets the voltage drop across the...

A Ratiometric Readout Circuit for Thermal-Conductivity-Based Resistive CO₂ Sensors

This paper reports a readout circuit for a resistive CO2 sensor, which operates by measuring the CO2-dependent thermal conductivity of air. A suspended hot-wire transducer, which acts both as a resistive heater and temperature sensor, exhibits a CO2-dependent heat loss to the surrounding air, allowing CO2 concentration to be derived from its...