The film acoustically-coupled transformer (FACT) has a first and second
decoupled stacked bulk acoustic resonators (DSBARs). Each DSBAR has a
lower film bulk acoustic resonator (FBAR), an upper FBAR atop the lower
FBAR, and an acoustic decoupler between them FBARs. Each FBAR has opposed
planar electrodes and a piezoelectric element between the electrodes. A
first electrical circuit interconnects the lowers FBAR of the first DSBAR
and the second DSBAR. A second electrical circuit interconnects the upper
FBARs of the first DSBAR and the second DSBAR. In at least one of the
DSBARs, the acoustic decoupler and one electrode of the each of the lower
FBAR and the upper FBAR adjacent the acoustic decoupler constitute a
parasitic capacitor. The FACT additionally has an inductor electrically
connected in parallel with the parasitic capacitor. The inductor
increases the common-mode rejection ratio of the FACT.