A 141-dB dynamic range CMOS gas-sensor interface circuit without calibration with 16-bit digital output word

In this paper, we present the design and the characterization of a wide-dynaihic-range interface circuit for resistive gas-sensors able to operate without calibration. The circuit is based on resistance-to-frequency conversion, which guarantees low complexity. The state-of-the-art of this measurement method has been improved first by separating the Resistance value Controlled Oscillator circuit (RCO) from the sensing device, thus leading to higher linearity performance, and then by exploiting a novel digital frequency measurement system. Measurement results on a silicon prototype, designed in a 0.35-mu m CMOS technology, show that the circuit achieves, without calibration, a precision in resistance measurement of 0.4 % over a range of 4 decades and better than 0.8% over 5 decades (dynamic range, DR = 141 dB). Furthermore, after calibration, it reaches a precision of 0.4% for resistance values ranging between 1 k Omega and 1 G Omega, thus leading to a DR of 168 dB. The prototype chip consumes less than 15 mW from a 3.3-V supply.