Design and modelling of a bidirectional front-end for resonating sensors based on pseudo floating gate amplifier

Abstract

In this paper, we characterize and model a bidirectional front-end based on pseudo-floating gate amplifier (PFGA) for actuation and read-out of resonating sensors. The basic idea consists of swapping the power supply of the PFGA in order to change the directionality of the front-end. A detailed description of the system has been discussed in this paper and supported by simulations and measurement results. A prototype has been fabricated using discrete components and tested with a real transducer (Murata MA40S4) and a Butterworth Van Dyke (BvD) load, which has proved to be proved to be a well approximated model for resonant sensors. The bidirectional amplifier has been implemented with the integrated circuit CD4007UB, which is a commercial discrete component containing low leakage MOSFET. The values chosen for the BvD load are Rb = 330 W, Lm = 60 mH, Cs = 450 pF, CE = 2.2 nF, which are approximately the same values of the lumped parameters reported in the data-sheet of the real sensor. This transducer is characterized by a nominal resonant frequency of 40 kHz. Measurement results show good fitting with the models developed in this work and the possibility to predict the sensor response by using the BvD load.