High mass resolution of sensors based on film bulk acoustic resonators (FBARs) is required for the detection of small molecules with the low concentration. An active control scheme is presented to improve the mass resolution of the FBAR sensors by adding a feedback voltage onto the driving voltage between two electrodes of the FBAR sensors. The feedback voltage is obtained by giving a constant gain and a constant phase shift to the current on the electrodes of the FBAR sensors. The acoustic ener
