RAPID TRACKING OF RESONANCE AND ANTIRESONANCE OF A PIEZOELECTRIC REASONATOR - A PHASE-LOCKED LOOP FOR CAPACITIVE LOADS

A simple phase detector/loop filter is devised which makes possible the tracking of resonances and antiresonances at which the sign of the phase angle remains positive. Successful lock-capture is observed at fundamental and higher-order modes of a PZT resonator for various values of initial frequency. Depending on Q-factor, final frequency values are affected more or less by the initial values. The overall lock-capture behavior is accounted for largely by computer simulations in which the VCO is described by a first-order delay function.