Lock-in amplifier powered analogue Q-control circuit for self-actuated self-sensing piezoelectric MEMS resonators

This paper presents a novel analogue Q-control circuit. A self-actuated and self-sensing piezoelectric microstructure in combination with a lock-in amplifier is used to provide a feedback signal with a substantially reduced noise level. This DC-value being proportional to the piezoelectric current is multiplied with a carrier sinusoidal signal on a custom-designed analogue printed circuit board applying an analogue amplifier IC. With this generated analogue feedback signal a complete analogue Q-control circuit is realized enabling faster response and as a consequence measurement cycles are less time consuming. Using this proposed Q-control technique, the Q-factor is increased from 397 to about 8,537 in air without pushing the feedback loop circuitry to stability limits. We believe that these promising results will stimulate further activities for a reliable on-line monitoring of even highly viscous liquids in the near future.