When a current flowing in a series circuit including an equivalent resistance, an equivalent inductor, and an equivalent capacitance in an electric equivalent circuit of a specific resonator in each filter is defined as an acoustic path current, under conditions that a phase of an acoustic path current of a first transmission filter at a side of a common terminal at a frequency within a first transmission band is represented as θ1.sub.Tx, a phase of an acoustic path current of the first transmission filter at the side of the common terminal at a frequency within a second transmission band is represented as θ2.sub.Tx, a phase of an acoustic path current of a first reception filter at the side of the common terminal at a frequency within the first transmission band is represented as θ1.sub.Rx, and a phase of an acoustic path current of the first reception filter at the side of the common terminal at a frequency within the second transmission band is represented as θ2.sub.Rx, a multiplexer satisfies a first condition: |(2.Math.θ1.sub.Tx−θ2.sub.Tx)−(2.Math.θ1.sub.Rx−θ2.sub.Rx)|=180°±90°, or a second condition: |(2.Math.θ2.sub.Tx−θ1.sub.Tx)−(2.Math.θ2.sub.Rx−θ1.sub.Rx)|=180°±90°.

An acoustic wave filter device includes at least one series arm resonator and a parallel arm resonator. The series arm resonators and the parallel arm resonator are defined by acoustic wave resonators, an interdigital transducer electrode of the series arm resonators is an apodized interdigital transducer electrode subjected to apodization weighting, in the interdigital transducer electrode of the parallel arm resonator, an intersecting portion includes a central region and low acoustic velocity regions provided at both outer side portions of the central portion, an acoustic velocity of an acoustic wave in the low acoustic velocity region is lower than an acoustic velocity of an acoustic wave in the central region, and a high acoustic velocity region where an acoustic velocity of an acoustic wave is higher than that of the low acoustic velocity region is provided at an outer side portion of each of the low acoustic velocity regions.

A radio-frequency filter includes a series-arm circuit on a circuit path that connects a first input/output terminal and a second input/output terminal. A parallel-arm circuit is connected to a node on the path and ground. The series-arm circuit includes a first impedance element, a first switch element connected to the first impedance element, and a series-arm resonator connected in parallel to the first impedance element and the first switch element. The parallel-arm circuit includes a first parallel-arm resonator, and a first switch circuit connected in series to the first parallel-arm resonator, the first switch circuit includes a second switch element. The first and second switch elements and the second switch elements include one or more transistors, and a gate width of the transistors included in the second switch element is larger than that of at least one of the transistors included in the first switch element.

Multi-mode surface acoustic wave filters are disclosed. A multi-mode surface acoustic wave filter can include a plurality of interdigital transducer electrodes that are longitudinally coupled to each other and acoustic reflectors on opposing sides of the plurality of interdigital transducer electrodes. The acoustic reflectors include acoustic reflector fingers arranged to suppress a spurious response due to shear horizontal mode of the multi-mode surface acoustic wave filter. For example, the acoustic reflector fingers can include stepped lengths and/or slanted pitches to suppress the spurious response due to shear horizontal mode.

Aspects of this disclosure relate to an acoustic wave filter that includes a multi-mode surface acoustic wave filter and a ladder section. The multi-mode surface acoustic wave filter has a higher impedance at an output than at an input. The ladder section is connected to the output of the multi-mode surface acoustic wave filter. Related radio frequency systems, radio frequency modules, wireless communication devices, and methods are disclosed.

In an elastic wave resonator, a first IDT electrode, a second IDT electrode, a first reflector, and a second reflector are located on a piezoelectric substrate. The first IDT electrode and the second IDT electrode share a shared bus bar. Between a first terminal and a second terminal, the first IDT electrode and the second IDT electrode are connected in parallel. The shared bus bar and the first reflector are connected to the first terminal. A first bus bar and a second bus bar are connected to the second reflector, and are further connected to the second terminal.

An elastic wave filter has an unbalanced signal terminal, first and second balanced signal terminals, and first through fifth IDT electrodes arranged in ordinal order between a pair of grating reflectors. Wiring electrodes of the third and fifth IDT electrodes are disposed adjacent a ground electrode of the fourth IDT electrode, wiring electrodes of the second and third IDT electrodes are disposed adjacent one another, and ground electrodes of the first and second IDT electrodes are disposed adjacent one another. The unbalanced signal terminal is connected to the wiring electrodes of the first, third, and fifth IDT electrodes, and the first and second balanced signal terminals are connected to the wiring electrodes of the second and fourth IDT electrodes, respectively. A pitch gradation of pitch spacing between electrode fingers in each of the first, second, and third IDT electrodes on one side of a center line in the third IDT electrode is gradually reduced by a first spacing α, and a pitch gradation of pitch spacing between electrode fingers in each of the third, fourth, and fifth IDT electrodes on the other side of the center line is gradually reduced by a second spacing β (β≠α), as the distance from the center line increases.

Aspects of the disclosure relate to wireless communication, and high-frequency filters with resonators. One example is a frequency band filter circuit having a split resonator. The split resonator comprises a resonator including a first section of a shared input busbar, a first section of a shared output busbar, and an electrode structure between the first section of the shared input busbar and the first section of the shared output busbar, the electrode structure configured for a resonance. The split resonator also comprises a detuned resonator. The detuned resonator includes a second section of the shared input busbar, a second section of the shared output busbar, and a detuned electrode structure between the second section of the shared input busbar and the second section of the shared output busbar, the detuned electrode structure configured for a detuned resonance different from the resonance.

An acoustic wave filter device includes a first longitudinally coupled acoustic wave resonator including an odd number of first IDT electrodes arranged along an acoustic wave propagation direction and a second longitudinally coupled acoustic wave resonator including an odd number of second IDT electrodes arranged in the acoustic wave propagation direction. Among the first IDT electrodes, the odd-numbered IDT electrodes are connected to a node and the even-numbered IDT electrodes are connected to a node. Among the second IDT electrodes, the odd-numbered IDT electrodes are connected to the node and the even-numbered IDT electrodes are connected to the node. The number of first IDT electrodes connected to the node and the number of second IDT electrodes connected to the node are the same.

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.