A multiplexer includes a transmission-side filter electrically connected to a common terminal and a transmission input terminal, and a transmission-side filter electrically connected to the common terminal and a transmission input terminal. The transmission-side filter includes a plurality of series arm resonators and a plurality of parallel arm resonators. Capacitance elements are respectively electrically connected in parallel to the series arm resonator and the parallel arm resonator, which are connected most proximately to the common terminal. IDT electrodes of a series arm resonator and a parallel arm resonator connected most proximately to the common terminal do not include a thinning electrode, and others of the series arm resonators and the parallel arm resonators include thinning electrodes.

A multiplexer includes a common terminal, a first terminal, a second terminal, and a third terminal, a first filter, a second filter, and a third filter. With a frequency f3 being defined as Mf1Nf2 or Mf2Nf1, M and N being natural numbers, f1 being a frequency included in a first passband of the first filter and f2 being a frequency included in a second passband of the second filter, at least a part of a range of frequency f3 overlaps a third passband of the third filter. No acoustic wave resonator is connected between the common terminal and a first parallel arm resonance circuit. A combined capacitance of the first parallel arm resonance circuit is higher than a minimum value of a combined capacitance of each of at least one first serial arm resonance circuit.

A transmission filter includes a transmission filter circuit and an additional circuit. The transmission filter circuit is provided between a first terminal and a second terminal. Between the first terminal and the second terminal, the additional circuit is connected in parallel with at least a portion of the transmission filter circuit. The additional circuit includes an IDT electrode group including a plurality of IDT electrodes located next to each other in an acoustic wave propagation direction and two reflectors that sandwich the IDT electrode group and having different numbers of pairs of electrode fingers.

An acoustic wave filter device includes first and second terminals, a longitudinally coupled resonator coupled between the first terminal and the second terminal, and an inductor connected between a path and a ground potential, the path connecting the first terminal and the longitudinally coupled resonator to each other. The longitudinally coupled resonator includes at least one first IDT electrode coupled to the first terminal, and at least one second IDT electrode connected to the second terminal. A total capacitance value of the at least one first IDT electrode is smaller than a total capacitance value of the at least one second IDT electrode.

A filter includes: a series-arm circuit; a first parallel-arm circuit connected to a ground and a node; and a second parallel-arm circuit connected to the ground and a node. The first parallel-arm circuit includes a parallel-arm resonator, and a first switch circuit. The second parallel-arm circuit includes a parallel-arm resonator, and a second switch circuit. The first switch circuit includes a first switch. The second switch circuit includes a second switch. A voltage across the first switch is lower than a voltage across the second switch. A stack count of the first switch is lower than a stack count of the second switch.

The acoustic wave element of the present invention includes a multi-mode type filter and a capacitance part. The multi-mode type filter includes a substrate comprised of a piezoelectric crystal; a first IDT to which a signal is input and a second IDT which is adjacent to this, each IDT including a first comb-shaped electrode and a second comb-shaped electrode which is connected to a reference potential, each comb-shaped electrode being located on the upper surface of the substrate and including a plurality of electrode fingers. The capacitance part is located on the upper surface of the substrate and includes a first counter electrode which is electrically connected to the first IDT at the first comb-shaped electrode side, and a second counter electrode which is arranged at a distance from the first counter electrode and is connected to the reference potential.

Embodiments of this application provide a filter and a method for adjusting performance of a filter, so as to quickly adjust performance of a filter. The filter includes at least two acoustic wave resonators; and a performance adjustment structure, connected to an output end of a first acoustic wave resonator and an input end of a second acoustic wave resonator, where the first acoustic wave resonator and the second acoustic wave resonator are any two of the at least two acoustic wave resonators, the performance adjustment structure includes a capacitor structure and/or an inductor structure, and the performance adjustment structure is configured to adjust an energy coupling mode between the first acoustic wave resonator and the second acoustic wave resonator.

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.

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 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.