A ladder type acoustic wave filter is disclosed. The acoustic wave filter can include a plurality of parallel arm resonators and a plurality of series arm resonators, in which an electromechanical coupling coefficient of a parallel arm resonator closest to an input node of the acoustic wave filter among the plurality of parallel arm resonators can be smaller than an electromechanical coupling coefficient of a series arm resonator closest to the input node among the plurality of series arm resonators.

A filter device includes a first path, a second path, and a capacitor. The first path includes at least one ladder filter circuit and connects a first terminal and a second terminal. The at least one ladder filter circuit includes a parallel arm resonator connected to a ground terminal. The second path includes a grounded resonator and is connected in parallel with any of the at least one ladder filter circuit. One end of the capacitor is connected to the second path, and the other end of the capacitor is connected to a third path which connects the parallel arm resonator and the ground terminal.

Certain aspects of the present disclosure provide a filter circuit and techniques for filtering using the filter circuit. The filter circuit generally includes a first filter stage having a first acoustic wave resonator coupled in a series path between a first port of the filter circuit and a second port of the filter circuit, a first inductor-capacitor (LC) tank circuit, a first capacitor coupled between a first terminal of the first acoustic wave resonator and the first LC tank circuit, the first LC tank circuit being coupled between the first capacitor and a reference potential node, and a second capacitor coupled between a second terminal of the first acoustic wave resonator and the first LC tank circuit. In some aspects, the filter circuit includes one or more other filter stages coupled to the first filter stage.

A circuit having a power amplifier port, an antenna port, and a ladder network coupled between the power amplifier and antenna ports is disclosed. The ladder network includes a proximal series acoustic resonator coupled to the power amplifier port, a distal series acoustic resonator coupled to the antenna port, and at least one series acoustic resonator coupled between the proximal series acoustic resonator and the distal series acoustic resonator. A first shunt acoustic resonator is coupled between a fixed voltage node and the proximal series acoustic resonator and the at least one series acoustic resonator. A second shunt acoustic resonator is coupled between the fixed voltage node and a second node to which the at least one series acoustic resonator is also coupled. A first inductor is coupled in parallel with the proximal series acoustic resonator to create notches below and above a passband of the ladder network.

A filter includes a piezoelectric film including lithium niobate or lithium tantalate, an acoustic wave resonator including a functional electrode on the piezoelectric film, a capacitor on the piezoelectric film and connected in parallel to the acoustic wave resonator, and a resonator electrically connected to the acoustic wave resonator. The functional electrode includes a pair of first and second electrodes facing each other in a direction intersecting a thickness direction of the piezoelectric film. When a thickness of the piezoelectric film is d and a center-to-center distance between the first electrode and the second electrode is p, d/p is smaller than or equal to about 0.5.

A high-frequency device includes: a circuit substrate including dielectric layers that are stacked, wiring patterns located on at least one of the dielectric layers, and a passive element formed of at least one of the wiring patterns, the circuit substrate having a first surface that is a surface of an outermost dielectric layer in a stacking direction of the dielectric layers; a terminal for connecting the high-frequency device to an external circuit, the terminal being located on the first surface and electrically connected to the passive element through a first path in the circuit substrate; and an acoustic wave element located on the first surface and electrically connected to the passive element through a second path in the circuit substrate.

A multi-stage matching network filter circuit device. The device comprises bulk acoustic wave (BAW) resonator device having an input node, an output node, and a ground node. A first matching network circuit is coupled to the input node. A second matching network circuit is coupled to the output node. A ground connection network circuit coupled to the ground node. The first or second matching network circuit can include an inductive ladder network including a plurality of series inductors in a series configuration and a plurality of grounded inductors wherein each of the plurality of grounded inductors is coupled to the connection between each connected pair of series inductors. The inductive ladder network can include one or more LC tanks, wherein each of the one or more LC tanks is coupled between a connection between a series inductor and a subsequent series inductor, which is also coupled to a grounded inductor.

A resonator element for use in a filter is provided. The resonator element includes a first resonator acoustically coupled to a second resonator. The first resonator has terminals for incorporation in a filter structure. A tuning circuit is coupled to the second resonator to enable tuning of the resonator element.

In an elastic wave filter device, a first filter including a first pass band and a second filter including a second pass band are common-connected at a common connection point. The first filter includes, on the common connection point side, a serial arm resonator, a parallel arm resonator, or a longitudinally coupled resonator-type elastic wave filter, and generates a fundamental wave and a high-order mode. A resonant frequency of the high-order mode on a higher frequency side relative to the first pass band of the first filter is smaller than the second pass band. On the common connection point side, a serial arm resonator in which the resonant frequency is not the highest, a parallel arm resonator, or a longitudinally coupled resonator-type elastic wave filter, is disposed.

An acoustic resonator filter includes at least one series acoustic resonator electrically connected between a first port and a second port in series, through which a radio frequency (RF) signal passes; at least one second shunt acoustic resonator electrically shunt-connected between the at least one series acoustic resonator and a ground; and at least one first shunt acoustic resonator electrically shunt-connected between the at least one series acoustic resonator and a ground and having a resonance frequency higher than a resonance frequency of the at least one second shunt acoustic resonator. At least one shunt acoustic resonator, among the at least one first shunt acoustic resonator and the at least one second shunt acoustic resonator has a temperature coefficient of frequency (TCF) corresponding to resonance frequency sensitivity more insensitive than resonance frequency sensitivity according to a change in temperature of the at least one series acoustic resonator filter.