Arrangement with two piezoelectric layers, and method of operating a filter device

A bulk acoustic resonator (BAW), comprising:

• 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;
• and
• the upper, lower and middle electrode electrodes are connected to circuitry that applies high-frequency signals to at least one of the two piezoelectric layers such that the bulk acoustic wave resonator has at least one resonance frequency when the circuitry is 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 circuitry is 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.

A filter device, comprising:

• a transmit (Tx) branch having at least one bulk acoustic wave resonator;
• a receiver (Rx) branch having at least one bulk acoustic wave resonator;
• and
• an antenna, which is connected to the Rx branch and to the Tx branch, wherein:
• each of the at least one bulk acoustic wave resonators 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 piezoelectric layers are capable of conductively isolating the middle electrode from the upper electrode and the lower electrode across the piezoelectric layers;
• and
• the upper, lower and middle electrode electrodes are connected to circuitry that applies high-frequency signals to at least one of the two piezoelectric layers such that each of the at least one of the bulk acoustic wave resonators of the Tx branch and the Rx branch have at least one resonance frequency when the circuitry is 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 circuitry is 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.