A filter includes a resonant circuit defining at least a portion of a signal path connected between a first terminal and a second terminal, an elastic wave resonator including one end that is grounded, a first inductor including one end connected to one end of the resonant circuit and another end connected to another end of the elastic wave resonator, and a second inductor including one end connected to another end of the resonant circuit and another end connected to the other end of the elastic wave resonator. The resonant circuit is an LC series resonant circuit in which a third inductor and first and second capacitors are connected in series with each other.

In accordance with an embodiment, a method of operating an RF system includes filtering a first wideband RF signal using a wideband filter bank. Filtering the first RF signal includes separating the first wideband RF signal into frequency cluster signals, where each frequency cluster signal of the frequency cluster signals includes different frequency ranges, the first wideband RF signal includes multiple RF bands, and each of the different frequency ranges comprises a plurality of RF bands of the multiple RF bands. The method further includes band stop filtering at least one of the frequency cluster signals to produce a band stopped frequency cluster signal.

A notch filter includes a first inductor coupled between an input node and an output node, a dual-resonator structure coupled between the input node and the output node, and a second inductor coupled between the dual-resonator structure and ground, and a bandpass filter includes a capacitor coupled between an input node and an output node, and a dual-resonator structure coupled between the input node, the output node, and ground.

An acoustic impedance matching device can facilitate acoustic transmission across an interface formed by materials having a very large acoustic impedance mismatch (e.g. air-water, or air-elastic polymer). The device can include a first medium. The first medium can have a first acoustic impedance. The device can include a second medium. The second medium can have a second acoustic impedance. The second acoustic impedance can be substantially greater than the first acoustic impedance. Thus, the first acoustic impedance and the second acoustic impedance are substantially mismatched. An interface can be defined between the first medium and the second medium. A bubble can be located in the second medium or the interface. The bubble can act as a resonator and can enable efficient sound transmission despite the large impedance mismatch of the first medium and the second medium.

Even when frequency characteristics are changed in association with multiple communication bands, an attenuation required for a specific frequency band outside a pass band is obtained. A frequency-variable filter (10) includes multiple series-arm resonators (111, 112, 113), multiple parallel-arm resonators (121, 122, 123), a variable capacitor (21), and an inductor (31) having a fixed inductance. The multiple series-arm resonators (111, 112, 113) and the multiple parallel-arm resonators (121, 122, 123) are connected in a ladder shape. The variable capacitor (21) is connected in series with the parallel-arm resonator (121). The fixed inductor (31) is connected in series with the parallel-arm resonator (123).

In accordance with an embodiment, a method of operating an RF system includes filtering a wideband RF signal using an adjustable center frequency bandpass filter to produce a filtered RF signal; amplifying the filtered RF signal to produce an amplified RF signal; and band stop filtering the amplified RF signal to produce a band stopped RF signal.

A ladder filter includes at least one series arm resonator connected in a path between first and second input/output terminals, at least two parallel arm resonators each connected between a connection node in the path and a ground, and an inductor connected in series to the at least one series arm resonator. The inductor is closer to the first input/output terminal than are the at least one series arm resonator and the at least two parallel arm resonators. Of the at least two parallel arm resonators, a first parallel arm resonator connected closest to the second input/output terminal has the highest anti-resonant frequency.

A radio-frequency module utilizing carrier aggregation includes a switch circuit that includes one input terminal and three or more output terminals and that simultaneously connects the input terminal and each of two or more output terminals selected from the output terminals, signal paths that propagate signals of corresponding frequency bands, band pass filters in the signal paths, and variable matching circuits in the signal paths. The circuit states of the variable matching circuits are changed in accordance with a combination of two or more signal paths simultaneously connected to the input terminal.

A ladder filter includes serial arm resonators disposed along a serial arm and parallel arm resonators disposed along corresponding parallel arms. Ladder circuit units are disposed along a path from an input terminal, which is a first end, to an output terminal, which is a second end. Each of the ladder circuit units includes a single serial arm resonator and a single parallel arm resonator. The ladder circuit units are mirror-connected to one another. The impedance at the first end is different from the impedance at the second end.

A method of fabricating an electronics package includes forming a cavity in a first surface of a semiconductor substrate, forming one or more passive devices on the semiconductor substrate, forming a microelectromechanical device on a piezoelectric substrate, and bonding the semiconductor substrate to the piezoelectric substrate with the microelectromechanical device disposed within the cavity.