Patent ID: 7459990

Claim:
A filter device, comprising: a transmit (Tx) branch having first and second bulk acoustic wave resonators; a receiver (Rx) branch having first and second bulk acoustic wave resonators; and an antenna, which is connected to the Rx branch and to the Tx branch, wherein: each bulk acoustic wave resonator of the Tx branch and the Rx branch further comprises two piezoelectric layers, a first layer of the two piezoelectric layers being arranged between an upper electrode and a middle electrode, and a second layer of the two piezoelectric layers being arranged between a lower electrode and the middle electrode; wherein the middle electrode and one of the upper and lower electrodes of each bulk acoustic wave resonator are connected to respective switches, and wherein the bulk acoustic wave resonators of the Tx branch and the Rx branch have a first resonance frequency when the switches are in a first switching state in which the upper and lower electrodes form input and output ports of the bulk acoustic resonator and at least one other resonance frequency different from the at least one resonance frequency when the switches are in a second switching state in which the middle electrode and one of the upper electrode and the lower electrode form input and output ports of the bulk acoustic resonator; wherein the piezoelectric layers are capable of conductively isolating the middle electrode from the upper electrode and the lower electrode across the piezoelectric layers.