Impedance transformation ratio control in film acoustically-coupled transformers

摘要

The acoustically-coupled transformer includes first and second stacked bulk acoustic resonators (SBARs), each having a stacked pair of film bulk acoustic resonators (FBARs) with an acoustic decoupler between them. In one embodiment, the acoustic decoupler comprises a layer of decoupling material has having a nominal thickness equal to an odd integral multiple of one quarter of the wavelength of an acoustic wave having a frequency equal to the transformer's center frequency. In another embodiment, the acoustic decoupler comprises a Bragg stack. Each FBAR has opposed planar electrodes with piezoelectric material between them. The transformer additionally has first terminals, second terminals, a first electrical circuit connecting one FBARs of the first SBAR to one FBAR of the second SBAR and the first terminals, and a second electrical circuit connecting the other FBAR of the first SBAR to the other FBAR of the second SBAR and the second terminals.