Uncalibrated integrable wide-range single-supply portable interface for resistance and parasitic capacitance determination

In this paper an uncalibrated fully integrable interface for wide-range resistance determination is presented. The proposed circuit, which implements a resistance-to-time conversion, is able to reveal more than six decades of resistance values (from 100 KΩ to more than 100 GΩ), typical of some resistive gas sensors, as well as to determine the sensor parallel capacitive component (in the order of few pF). The proposed front-end has been designed both to work with a single-supply voltage (3.3 V), so it is suitable in low-cost portable applications, and to simplify the integration in a standard CMOS technology together with the digital components needed for the time measurement. Post-layout simulations on the designed integrated solution (in a standard CMOS technology) and experimental results, using a discrete-component prototype, both on passive components and on real sensors (MoW-based metal oxide sensors) have shown high linearity and reduced percentage error with respect to the theoretical expectations.