Acoustically coupled resonator filter with impedance transformation ratio controlled by resonant frequency difference between two coupled resonators

Abstract

A signal processing device includes a first acoustic resonator, a second acoustic resonator disposed on the first acoustic resonator, and a coupling layer between the first and the second acoustic resonators. The first acoustic resonator has a first electrical impedance and a first resonance frequency and includes a first set of electrodes, and a first piezoelectric layer having a first thickness, disposed between the first set of electrodes. The second acoustic resonator has a second electrical impedance and a second resonance frequency, and includes a second set of electrodes, and a second piezoelectric layer having a second thickness, wherein the second piezoelectric layer is disposed between the second set of electrodes. The first electrical impedance at a passband frequency of the device substantially differs from the second electrical impedance at the passband frequency of the device. The first and second resonance frequencies are substantially different from each other.