Authors: A. Arnau, T. Sogorb, Y. Jiménez

Event: QCM 2002: Chemical, Biological and Pharmaceutical applications of acoustic sensor technologies. Brighton, UK (2002)

 

A sensor-controlled oscillator tracks the frequency for a certain sensor phase, therefore, changes in the motional resistance or in the parallel capacitance produce erroneous changes in the oscillating frequency. These erroneous changes would not take place if the parallel capacitance were precisely compensated and the phase of the sensor for oscillating condition were 0º. This reveals that the so-called static capacitance of the sensor is one of the elements which make the use of oscillators more critical for sensors applications. A phase-locked-loop based circuit designed for compensating the parallel capacitance in quartz crystal resonator sensors is presented. The results reported prove the reliability of the proposed system for quartz sensors. This circuit compensates the parallel capacitance and permits the calibration of the external circuitry to the sensor, in addition provides a continuous measurement of the motional series resonant frequency and motional resistance. Preliminary experimental results using this circuit as a biosensor are also shown.