A fully integrated interface circuit for 1.5°C accuracy temperature control and 130-dB dynamic-range read-out of MOX gas sensors

This paper presents a complete gas-sensing chip. It consists of a high-efficiency temperature control loop with a switching power stage and digital set-point and of a wide-dynamic-range interface circuit able to operate without calibration. Measurements results show that the controlled temperature of the sensor over a range of 250degC exhibits an accuracy better than 1.5degC with a maximum peak-to-peak ripple of 1.0degC. The read-out circuit achieves, without calibration, a precision in sensor resistance measurement of 2.65% over a range of 5.3 decades (Dynamic Range, DR=138 dB). The overall system is flexible and can be interfaced to sensors with different fabrication parameters. The prototype chip, designed in a 0.35-mum CMOS technology, includes on the same 10-mm² die the precision read-out circuit and the switching power stage. In spite of the interferences produced by the power stage, the read-out circuit maintains always a DR performance above 130 dB.