A new interface for resistive chemical sensors with low measuring time

Abstract

The main issue concerning metal oxide (MOX) gas sensors is mostly related to the wide range of resistive values the sensors can show. In addition, some sensors could have baseline resistive value up to tens of gigohms. To avoid the use of expensive pico-amperometers, different solutions have been recently proposed, exploiting the resistance-to-time conversion (RTC) technique. They show good linearity and are suitable for the integration in a chip together with the elaboration unit, but they may require long measurement time (tens of seconds) if high resistance values need to be estimated. In this work, a new method is proposed to reduce the measuring time, keeping the advantages offered by the RTC approach. The applicability of the interface is therefore extended for solutions requiring detailed information of the sensor response, such as the characterization of new sensors (e.g. nanowires) or the behavior analysis during non-standard thermal profiles. Particularly, an effective architecture, based on moving thresholds, has been proposed, simulated and experimentally tested with commercial resistors (values between 1 MΩ and 100 GΩ).

A complementary metal oxide semiconductor—integrable conditioning circuit for resistive chemical sensor management

“…Furthermore, by adopting a double threshold approach, as in [17], the parasitic capacitance C sens can be estimated starting from the sensor ramp gap occurring during the switching of sensor bias voltage V exc [18,19]. The timing diagram related to the sensor and threshold ramps is shown in figure 2, where the choice of a positive and single supply (V cc ) is clearly visible.…”