A novel time-controlled interface circuit for resistive sensors

In this paper we present a novel interface circuit, suitable for wide range resistive sensors, capable to overcome the main limit of the circuits based on resistance-to-time (R-T) conversion approach, that is the long measuring time occurring in the evaluation of high-value sensor resistances. This solution is based on a particular oscillating circuit architecture which performs a “compression” of the higher part of the resistive range, thus limiting the measuring time. The interface is simply implemented by Operational Amplifiers (OAs) and passive components and is suitable to be integrated in a single chip. Since it employs an AC excitation voltage for the sensor, this front-end results to be capable to estimate both the sensor resistance over a wide range (5 decades) and its in-parallel parasitic capacitance, for diagnosis purposes and complete characterization of the sensor. PSpice simulation results have shown the feasibility of the proposed approach; in addition, experimental measurements, conducted through the fabricated prototype PCB and utilizing commercial sample resistors and capacitors to emulate sensor behaviour, have shown good performance in the resistive range 100kΩ-10GΩ with a maximum measuring time set to about 70ms, so confirming the theoretical expectations and the validity of the proposed sensor interface.