Filter characteristics of a first filter are improved while suppressing degradation in filter characteristics of a second filter. A multiplexer includes a first terminal, a second terminal, a first filter, a second filter, and a capacitive element. The first filter and the second filter are connected to an antenna via the first terminal. The first filter includes a plurality of series arm resonators, a plurality of parallel arm resonators, and an inductor. The inductor is provided between the parallel arm resonator and ground. A first end portion of the capacitive element is connected to a first path at a position in between the series arm resonator that is the closest to the first terminal and the second terminal. A second end portion of the capacitive element is connected between the parallel arm resonator and the inductor.

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.

There are disclosed acoustic resonators and radio frequency filter devices. A back surface of a single-crystal piezoelectric plate is attached to a surface of a substrate except for portions of the piezoelectric plate forming a plurality of diaphragms, each of which spans a respective cavity in the substrate. A conductor pattern is formed on the front surface, the conductor pattern including interdigital transducers (IDTs) of one or more pairs of sub-resonators, each pair consisting of two sub-resonators. The IDT of each sub-resonator includes interleaved fingers disposed on a respective diaphragm. The piezoelectric plate and the IDTs are configured such that respective radio frequency signals applied to each IDT excite respective shear primary acoustic modes in the respective diaphragms. The two sub-resonators of each pair of sub-resonators are positioned symmetrically about a central axis.

Aspects of this disclosure relate to bandpass filters with enhanced out of band rejection. The bandpass filters include a stage that is modified using a network of three inductors two of which are mutually coupled inductors. Related methods, radio frequency systems, radio frequency modules, and wireless communication devices are also disclosed.

A filter (22A) includes: a series arm circuit (11) that is connected between an input/output terminal (22m) and an input/output terminal (22n); and a parallel arm circuit (12) that is connected between a node (x1), which is on a path that connects the input/output terminal (22m) and the input/output terminal (22n), and ground. The parallel arm circuit (12) includes a parallel arm resonator (22p) and an impedance circuit (13) that is serially connected to the parallel arm resonator (22p). The impedance circuit (13) includes a first impedance element, which is one of an inductor and a capacitor, a second impedance element, which is the other of an inductor and a capacitor, and a switch (22SW) that is serially connected to the second impedance element. A first series circuit (14) comprising of the second impedance element and the switch (22SW) is connected in parallel with the first impedance element.

An acoustic wave device, a radio frequency filter and an electronics module are provided. The acoustic wave device comprises a piezoelectric substrate, a temperature compensation layer disposed on the piezoelectric substrate, and an interdigital transducer embedded within the temperature compensation layer and spatially separated from the piezoelectric substrate. The interdigital transducer is configured to generate an acoustic wave in response to an electrical signal. A passivation layer is disposed on the temperature compensation layer. The acoustic wave device can be used in wide passband applications, and has an excellent temperature coefficient, small size, and a clean response.

A surface acoustic wave filter includes series and parallel arm resonance sections. The series arm resonance section is in a series arm. The parallel arm resonance section is in a parallel arm. The series arm resonance section includes one or more surface acoustic wave devices. Each surface acoustic wave device includes a first resonator group and a second resonator group. The first and second resonator groups are connected in parallel and include surface acoustic wave resonators. The first resonator group includes at least one surface acoustic wave resonator. The second resonator group includes a greater number of surface acoustic wave resonators than the at least one surface acoustic wave resonator in the first resonator group. The resonant frequency of the surface acoustic wave resonator in the first resonator group is higher than the resonant frequency of the surface acoustic wave resonators in the second resonator group.

An electronic filter comprises a high pass section (110) and a low pass section (120). The high pass section includes at least one filter stage of a series-connected acoustic resonator (111) and a parallel connected inductor (114). The low pass section comprises at least one filter stage including a series-connected inductor (121) and a parallel connected acoustic resonator (123). The filter is useful for a communication device covering the n79 5G band.

An acoustic wave filter includes a substrate and a piezoelectric layer over the substrate. First acoustic wave resonators are disposed over the piezoelectric layer and arranged in series along a first branch, and second acoustic wave resonators are disposed over the piezoelectric layer, arranged in parallel, and connected to the first branch and to ground. The first and second acoustic wave resonators include an interdigital transducer electrode interposed between a pair of reflectors. A layer of negative temperature coefficient of frequency dielectric material is disposed over one or more of the second plurality of acoustic wave resonators to control the temperature coefficient of frequency and improve temperature stability of the acoustic wave filter.

A filter device includes a port, a reference potential part, at least one filter, a signal line, a first inductor, and at least one second inductor. A signal is input through the port, and/or a signal is output through the port. The reference potential part is placed at a reference potential. The at least one filter filters a signal. The signal line connects the port to the at least one filter. The first inductor is at least part of the signal line. The second inductor forms a connection between the signal line and the reference potential part. The first inductor and the at least one second inductor are inductively coupled to each other.