Patent ID: 6946928

Claim:
An acoustically-coupled transformer having a pass band characterized by a center frequency the transformer comprising: a first stacked bulk acoustic resonator (SBAR) and a second SBAR, each SBAR comprising: a stacked pair of film bulk acoustic resonators (FBARs), each of the FBARs comprising opposed planar electrodes and a layer of piezoelectric material between the electrodes, and an acoustic decoupler between the FBARs, the acoustic decoupler comprising a layer of acoustic decoupling material having nominal thickness equal to an odd integral multiple of one quarter of the wavelength in the acoustic decoupling material of an acoustic wave having a frequency equal to the center frequency; first terminals; second terminals; a first electrical circuit connecting one of the FBARs of the first SBAR to one of the FBARs of the second SBAR and to the first terminals, and a second electrical circuit connecting the other of the FBARs of the first SBAR to the other of the FBARs of the second SBAR and to the second terminals.