An acoustic wave filter device includes a ground connection terminal connected to an external ground electrode, a serial arm resonator, a first parallel arm circuit connected to a first node of the serial arm resonator, the first node being positioned closer to an input/output terminal, and to the ground connection terminal, and a second parallel arm circuit connected to a second node of the serial arm resonator, the second node being positioned closer to an input/output terminal, and to the ground connection terminal. The first parallel arm circuit includes a parallel arm resonator having a resonant frequency higher than a center frequency of a filter pass band, and a frequency varying circuit connected to the parallel arm resonator and the ground connection terminal. The second parallel arm circuit includes a parallel arm resonator having a resonant frequency higher than the center frequency of the filter pass band.

A filter device according to an embodiment of the present disclosure includes a first filter and a second filter that are connected in parallel between a first terminal and a second terminal. The first filter includes multiple series arm resonators. The series arm resonators are disposed in series in a path from the first terminal via the first filter to the second terminal. The series arm resonators include a first series arm resonator and a second series arm resonator. Under a condition that a value obtained by dividing a difference between an antiresonance frequency and a resonance frequency of each series arm resonator by the resonance frequency is defined as a fractional bandwidth, a first fractional bandwidth of the first series arm resonator is different from a second fractional bandwidth of the second series arm resonator.

A filter device includes a first filter and a second filter. The first filter and the second filter are disposed in parallel between a first terminal and a second terminal. A first passband of the filter device includes at least part of a second passband of the first filter. The first passband includes at least part of a third passband of the second filter. The second passband is narrower than the first passband. The third passband is narrower than the first passband. The third passband has a center frequency higher than a center frequency of the second passband. The first filter includes multiple elastic wave resonators and a first capacitive element. The first capacitive element is connected in parallel with the first elastic wave resonator.

A radio-frequency filter includes a first series-arm circuit and a second series-arm circuit that is on a circuit path closer to the output terminal than the first series-arm circuit. A first parallel-arm circuit is connected to a ground and a node on the path between the first series-arm circuit and the second series-arm circuit. The first series-arm circuit includes a first series-arm resonator, and a first switch element, the first switch element including first semiconductor elements arranged in series. The second series-arm circuit includes a second series-arm resonator, and a second switch element, the second switch element including at least one second semiconductor element. A first stack number being higher than a second stack number, the first stack number being a number of the first semiconductor elements and the second stack number being a number of the one or more second semiconductor elements.

A filter (11) includes a series-arm circuit (10) connected between an input/output terminal (11m) and an input/output terminal (11n); and a parallel-arm circuit (20) connected between a ground and a path that connects the input/output terminal (11m) and the input/output terminal (11n). One circuit among the series-arm circuit (10) and the parallel-arm circuit (20) is constituted by a parallel-arm resonator (p1) and a parallel-arm resonator (p2) that are connected in parallel to each other and that are connected to a node (x1) on the path. The parallel-arm resonators (p1) and (p2) form a pass band, together with another circuit among the series-arm circuit (10) and the parallel-arm circuit (20). The parallel-arm resonator (p2) has a resonant frequency lower than a resonant frequency of the parallel-arm resonator (p1) and has an impedance higher than an impedance of the parallel-arm resonator (p1).

A filter includes a series-arm resonator connected on a path connecting input/output terminals, and first and second parallel-arm resonators that are connected between the same node on the path and ground. A resonant frequency of the second parallel-arm resonator is higher than a resonant frequency of the first parallel-arm resonator, and an anti-resonant frequency of the second parallel-arm resonator is higher than an anti-resonant frequency of the first parallel-arm resonator. Each of the first and second parallel-arm resonators is defined by an acoustic wave resonator including an IDT electrode. The IDT electrode in the second parallel-arm resonator has a lower aspect ratio than the IDT electrode in the first parallel-arm resonator, where the aspect ratio is a ratio of an overlap width of electrode fingers to the number of pairs of electrode fingers.

Embodiments of resonator circuits and modulating resonators and are described generally herein. One or more acoustic wave resonators may be coupled in series or parallel to generate tunable filters. One or more acoustic wave resonances may be modulated by one or more capacitors or tunable capacitors. One or more acoustic wave modules may also be switchable in a filter. Other embodiments may be described and claimed.

A radio-frequency filter (10) includes a series arm circuit (11) and a parallel arm circuit (12). The series arm circuit (11) includes a series arm resonator (s1a) and a variable frequency circuit (11b) connected in parallel with the series arm resonator (s1a). The variable frequency circuit (11b) includes a series arm resonator (s1b) and a switch (SWb) connected in series with the series arm resonator (s1b). The variable frequency circuit (11b) is configured to change at least one of a resonant frequency that provides a pass band of the radio-frequency filter (10) and an anti-resonant frequency that provides an attenuation pole of the radio-frequency filter (10). A resonant frequency of the series arm resonator (s1b) is different from a resonant frequency of the series arm resonator (s1a).

A filter includes a series-arm resonator located on a path that connects an input/output terminal (11m) with an input/output terminal (11n), and a first parallel-arm resonant circuit connected between a node, which is located on the path, and ground. The first parallel-arm resonant circuit includes a parallel-arm resonator, and a pair of a capacitor and a switch connected in parallel with each other and in series with the parallel-arm resonator between the parallel-arm resonator and ground. An interconnect line (a1) is connected to the input/output terminal (11m), and an interconnect line (a2) is connected to the input/output terminal. The parallel-arm resonator and the switch are connected by an interconnect line (a3). The interconnect line (a3) has a characteristic impedance lower than a characteristic impedance of the interconnect line (a1) or a characteristic impedance of the interconnect line (a2).

A tunable notch filter is disclosed with a first acoustic resonator coupled in series with a first inductive element between a filter input node and a filter output node. A first capacitor is coupled in parallel with the first acoustic resonator and the first inductive element. In at least one embodiment, the first capacitor is configured to have variable capacitance that is electronically tunable by way of an electronic controller. A second acoustic resonator is coupled in series with a second inductive element between the filter output node and a signal ground node. A second capacitor is coupled in parallel with the second inductive element. In at least one embodiment, the second capacitor is electronically tunable. The tunable notch filter is configured to provide a highly selective notch filter response between the filter input node and the filter output node with high attenuation.