A multiplexer includes first and second filters connected to a common terminal. The second filter has a pass band on a higher frequency side with respect to a pass band of the first filter. The first filter includes a series arm circuit, and a parallel arm circuit having a resonant frequency on a lower frequency side with respect to a frequency at a low frequency end of a pass band of the first filter, and the series arm circuit includes a series arm resonator having a resonant frequency in the pass band of the first filter and a series arm resonator that is electrically connected in parallel to the series arm resonator and that has a resonant frequency on a higher frequency side with respect to a frequency at a high frequency end of the pass band of the first filter.

A filter device includes a first input/output terminal and a second input/output terminal, as well as a series-arm circuit disposed on a path that connects the first input/output terminal and the second input/output terminal, and a parallel-arm circuit connected to a node on the path and a ground. At least one of the series-arm circuit or the parallel-arm circuit includes a resonance circuit, and the resonance circuit includes a first acoustic wave resonator, and a first capacitor connected in parallel to the first acoustic wave resonator, and having a greater electrostatic capacitance per unit area than that for the first acoustic wave resonator.

Techniques are disclosed implementing acoustic wave resonator (AWR) filter architectures to enable integrated solutions requiring significantly less passive components. The primary AWR filter topology leverages the use of parallel resonator branches, each having a relatively narrow bandwidth that may be combined to form an overall broadband filter response. This architecture may be further modified using electronically-controlled switching components to dynamically turn specific branches on or off to tune the filter, thus realizing a programmable broadband solution. Shunt resonators may also be added to the AWR filter topology, which may also be controlled with the use of electronically-controlled switching components to provide further control with respect to roll-off and the location and number of notch frequencies.

A radio-frequency filter (10) includes a series arm circuit (11) and a parallel arm circuit (12). The series arm circuit (11) is disposed on a path connecting an input/output terminal (11m) and an input/output terminal (11n). The parallel arm circuit (12) is connected to a ground and to a node (x1) on the path. The series arm circuit (11) includes a series connecting circuit (11e) and a first variable frequency circuit (11a). The series connecting circuit (11e) includes a series arm resonator (s1) and a capacitor (C1). The first variable frequency circuit (11a) is connected in parallel with the series connecting circuit (11e) and varies the anti-resonant frequency of the series arm circuit (11). The first variable frequency circuit (11a) includes a capacitor (C2) and a switch (SW1) connected in series with each other. The series arm resonator (s1) and the capacitor (C1) are connected in series with each other.

The acoustic wave filter (10A) includes a parallel-arm resonant circuit (12p). The parallel-arm resonant circuit (12p) includes a parallel-arm resonator (p1) and a frequency variable circuit (72p) that are connected in parallel. The frequency variable circuit (72p) includes a parallel-arm resonator (p2) that has a resonant frequency higher than that of the parallel-arm resonator (p1) and a switch (SW1) element. A frequency difference between a resonant frequency on a higher frequency side of the parallel-arm resonant circuit (12p) in a case where the switch (SW1) is OFF and a resonant frequency on a higher frequency side of the parallel-arm resonant circuit (12p) in a case where the switch (SW1) is ON is equal to or more than a frequency difference between a low frequency end frequency of the second attenuation band and a low frequency end frequency of the first attenuation band.

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 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 variable filter includes a serial arm resonator and a parallel arm resonance circuit, the parallel arm resonance circuit includes a parallel arm resonator and a capacitance element connected to the parallel arm resonator, the serial arm resonator and the parallel arm resonator respectively include IDT electrodes each formed of a plurality of electrode fingers formed on a substrate, and a film thickness of the plurality of electrode fingers of the parallel arm resonator is larger than a film thickness of the plurality of electrode fingers of the serial arm resonator.

An acoustic wave filter includes series arm resonators, and a parallel arm resonator provided in a second path connecting a ground and a node connecting the series arm resonators. Each of the series arm resonators includes a piezoelectric body and an interdigital transducer electrode. One of the series arm resonators includes a second adjusting film that adjusts Ksaw. An anti-resonant frequency of the other one of the series arm resonators is higher than an anti-resonant frequency of the one of series arm resonators. An adjusting film that adjusts Ksaw is not provided in the other one of series arm resonators, or when a first adjusting film that adjusts Ksaw is provided in the other one of the series arm resonators, the first adjusting film is thinner than the second adjusting film.

A resonator device may include a stacked first resonator and second resonator. The first resonator may be configured to resonate at a first operating frequency, and the second resonator may be configured to resonate at a second operating frequency different from the first operating frequency. The first resonator may include a first electrode and a first active layer arranged over the first electrode. The second resonator may include a second active layer arranged over the first active layer, and a second electrode arranged over the second active layer. The stacked first resonator and second resonator may be coupled to a reconfiguration switch for selectively operating at the first operating frequency or the second operating frequency. One of the first resonator and the second resonator is active upon selection by the reconfiguration switch, while the other resonator is inactive.