A tunable filter using acoustic resonators is disclosed. A tunable filter includes a plurality of tunable resonator units (20). Each tunable resonator unit (20) has acoustic wave resonators (12). Each acoustic wave resonator is associated with a different tunable frequency. Each tunable resonator unit also has a first switch (22) configured to select one of the plurality of acoustic wave resonators of the tunable resonator unit at a time. The first switches of the plurality of tunable resonator units are coupled to cooperatively select one acoustic wave resonator in each one of the plurality of tunable resonator units, where a selected acoustic wave resonator in a tunable resonator unit of the plurality of tunable acoustic resonator units is associated with a same tunable frequency response as the other selected acoustic resonators of the others of the plurality of tunable acoustic resonator units. The selection results in an overall tunable frequency response.

A resonator element for use in a filter is provided. The resonator element includes a first resonator acoustically coupled to a second or third resonator or both. The first resonator has terminals for incorporation in a filter structure. A tuning circuit is coupled to the second or third resonator or both to enable tuning of the resonator element. The tuning circuit includes a variable capacitor and an inductor.

A resonator element for use in a filter is provided. The resonator element includes a first resonator acoustically coupled to a second or third resonator or both. The first resonator has terminals for incorporation in a filter structure. A tuning circuit is coupled to the second or third resonator or both to enable tuning of the resonator element. The tuning circuit includes a variable capacitor and an inductor.

A radio-frequency filter (10) includes a series arm resonator (s1) connected between input/output terminals (11m and 11n) and parallel arm circuits (110 and 120) connected to a node (xl) and a ground. The parallel arm circuit (110) includes a parallel arm resonator (p1) and a variable frequency circuit (110A) connected in series with each other between the node (xl) and a ground. The variable frequency circuit (110A) changes the resonant frequency of the parallel arm circuit (110). The variable frequency circuit (110A) is connected in series with the parallel arm resonator (p1) and includes a capacitor (C1) and a switch (SW1) connected in parallel with each other. The parallel arm circuit (120) includes a capacitor (C2) and a switch (SW2) connected in series with each other between the node (x1) and a ground.

A radio-frequency filter (10) includes a series arm resonator (s1) connected between input/output terminals (11m and 11n) and parallel arm circuits (110 and 120) connected to a node (xl) and a ground. The parallel arm circuit (110) includes a parallel arm resonator (p1) and a variable frequency circuit (110A) connected in series with each other between the node (xl) and a ground. The variable frequency circuit (110A) changes the resonant frequency of the parallel arm circuit (110). The variable frequency circuit (110A) is connected in series with the parallel arm resonator (p1) and includes a capacitor (C1) and a switch (SW1) connected in parallel with each other. The parallel arm circuit (120) includes a capacitor (C2) and a switch (SW2) connected in series with each other between the node (x1) and a ground.

In accordance with an embodiment, an RF system includes a transmit path having a transmit RF filter and an adjustable transmit phase shifter/matching network coupled between the transmit RF filter and a transmit antenna port, where the adjustable transmit phase shifter/matching network is configured to transform an impedance of the transmit RF filter at a receive frequency from a first lower impedance to a first higher impedance at the transmit antenna port; and a receive path having a receive RF filter and an adjustable receive phase shifter/matching network coupled between the receive RF filter and a receive antenna port, where the adjustable receive phase shifter/matching network is configured to transform an impedance of the receive RF filter at a transmit frequency from a second lower impedance to a second higher impedance at the receive antenna port.

In accordance with an embodiment, an RF system includes a transmit path having a transmit RF filter and an adjustable transmit phase shifter/matching network coupled between the transmit RF filter and a transmit antenna port, where the adjustable transmit phase shifter/matching network is configured to transform an impedance of the transmit RF filter at a receive frequency from a first lower impedance to a first higher impedance at the transmit antenna port; and a receive path having a receive RF filter and an adjustable receive phase shifter/matching network coupled between the receive RF filter and a receive antenna port, where the adjustable receive phase shifter/matching network is configured to transform an impedance of the receive RF filter at a transmit frequency from a second lower impedance to a second higher impedance at the receive antenna port.

A notch filter includes an inductor coupled between an input node and an output node, and a dual-resonator structure coupled between the input node, the output node, and ground.

A notch filter includes an inductor coupled between an input node and an output node, and a dual-resonator structure coupled between the input node, the output node, and ground.

A bandpass filter includes a capacitor coupled between an input node and an output node, and a dual-resonator structure coupled between the input node, the output node, and ground.