System-level design of a readout circuit with thermostatic control for a MEMS pellistor sensor

Catalytic flammable gas sensors detect the presence of flammable gasses in air at a non-dangerous concentration level, thus helping in the prevention of explosion risks. These devices are usually operated without thermal control i.e. they measure the temperature increase of a detector induced by the catalytic combustion of the flammable gas. We propose the system-level design of a bias and readout system that directly measures the heat produced by the catalytic combustion. The proposed solution operates the sensor at a constant temperature via a feedback scheme that contains two thermal feedback loops. We chose a feedback control that uses pulse-density modulation, thus the proposed system implements a direct analog-to-digital conversion of the heat produced by the catalytic combustion. In practice, this mixed-signal front-end for pellistors is expected to extend the functionality and precision of the sensor while providing with a simple implementation.