AN-Z2V: Autonulling-Based Multimode Signal Conditioning Circuit for R-C Sensors

Abstract

In this article, we propose an autonulling-based multimode impedance-to-voltage converter (AN-Z2V) signal conditioning circuit for resistive-capacitive (R-C) sensors. The proposed technique takes advantage of the reuse of the phase tracking and autonulling modules to extract the in-phase and quadrature components of the sensors. The circuit is designed for three sensing modes: 1) Mode-C for capacitive sensors with leakage resistor; 2) Mode-R for resistive sensors with parasitic shunt capacitor; and 3) Mode-Z for impedance R-C sensor. A novel autotuning quadrature phase generator circuit is designed and implemented for the generation of reference 90° phase-shifted signal for the leaky capacitive sensors. A prototype of the proposed circuit is fabricated and tested. Measurement results show that AN-Z2V provides the measurement range with low relative error compared with the reported systems. The system is tested for a range of 10-760 pF and 56 kQ-6.5 MQ for mode-C and mode-R, respectively. The accuracy of the proposed circuit is found to be ±0.11% and ±0.07% for mode-C and mode-R, respectively. The capacitance and resistance of the impedance R-C sensor are simultaneously measured in mode-Z for a range of 33-528 pF and 100 kQ-7.8 MQ, respectively.