An exemplary tunable circuit includes an inductor coupled to a node and a first capacitor coupled to the node. The tunable circuit also includes a variable capacitor coupled to the node, such that a total capacitance of the tunable circuit depends on a fixed capacitance of the first capacitor and a variable capacitance of the variable capacitor. In an example, the inductor and the first capacitor are both included in a passive device and the variable capacitor is in a semiconductor device. The variable capacitor allows the total capacitance to be modified for the purpose of, for example, calibrating the capacitance to account for manufacturing variations, and/or adjusting to a frequency range of operation used by wireless devices in a region of the world. The first capacitor may be a higher quality capacitor providing a larger portion of the total capacitance than the variable capacitor.

A stacked composite filter device includes a stacked body having a first region and a second region that are different from each other. A first filter includes a first inductor and has a first pass band is arranged in the first region. A second filter includes a second inductor and has a second pass band on a lower frequency side than the first pass band is arranged in the second region. A first conductive structure extends in a stacking direction of the stacked body and includes one end grounded that is arranged in an area that is in the first region and adjacent to the second region. The other end of the first conductive structure is connected to the first inductor.

A diplexer includes a common terminal, first and second terminals, and first and second filters which are electrically connected to the common terminal. The first filter passes a high frequency signal in a first frequency band. The second filter passes a high frequency signal in a second frequency band higher than the first frequency band. Each filter includes an inductor and a capacitor in a dielectric substrate. The first filter includes a first inductor with one end electrically connected to the common terminal, and a first capacitor electrically connected between another end of the first inductor and a ground. An inductance of the first inductor is smaller than an inductance of another inductor included in the first filter. A frequency of an attenuation pole defined by the first inductor and the first capacitor is higher than a frequency of the second frequency band.

A radio frequency module (1) includes a first switch (4), an attenuation filter (3), and a plurality of band pass filters (12A to 12C, 22A to 22C). The first switch (4) is a switch that is capable of simultaneously connecting a common terminal (40) to selection terminals (41, 42) out of a plurality of selection terminals (41 to 43). The plurality of band pass filters (12A to 12C, 22A to 22C) include a first band pass filter (22A) and a second band pass filter (22B). The attenuation filter (3) includes at least one reactive element out of an inductive element and a capacitive element. In the radio frequency module (1), the reactive element is adjacent to at least one band pass filter out of the plurality of band pass filters (12A to 12C, 22A to 22C).

A low pass filter includes a first inductor, a second inductor magnetic-field-coupled to the first inductor, a third inductor, and a first capacitor. The first inductor is electrically connected between a first port and an intermediate node, being a node to which the second inductor is electrically connected, between the first inductor and the second port. The second inductor is electrically connected between the intermediate node and a ground terminal. The third inductor is electrically connected between the intermediate node and the second port, and a first parallel resonant circuit is defined by the third inductor and the first capacitor. The first inductor and the second inductor are coupled to each other in such a relationship that a negative inductance is generated between the intermediate node and the third inductor due to magnetic field coupling between the first inductor and the second inductor.

A high frequency filter includes series arm resonators and parallel arm resonators as acoustic wave resonators and at least one inductor, wherein capacitive components of the acoustic wave resonators constitute an LPF and an HPF as hybrid filters with an inductor or with an inductor and a capacitor, and the at least one inductor includes inductors as mount component inductors.

A signal processing system includes: an interference source; and a band-stop filter. A first terminal of the band-stop filter is electrically connected to the interference source, a second terminal of the band-stop filter is grounded, and the band-stop filter is configured to filter a baseband signal output by the interference source. The interference source includes a first main board; or the interference source includes a target module and a metal frame used for fastening the target module, and the target module is a display module or a camera module.

Aspects of this disclosure relate to hybrid acoustic LC filter with harmonic suppression. The hybrid acoustic LC filter includes a hybrid passive/acoustic and a non-acoustic LC filter cascaded with the hybrid passive/acoustic filter. The hybrid passive/acoustic filter can be configured to filter a radio frequency signal. The hybrid passive/acoustic filter can include acoustic resonators and a non-acoustic passive component. The non-acoustic LC filter can be configured to suppress a harmonic of the radio frequency signal. The non-acoustic LC filter can be a low pass filter or a harmonic notch filter, for example. Related multiplexers, wireless communication devices, and methods are disclosed.

Aspects of this disclosure relate to a radio frequency system with tunable notch filtering. The radio frequency system includes a first tunable filter and a second tunable filter. The first tunable filter is coupled between an output of a power amplifier and a radio frequency switch. The second tunable filter includes mutually coupled inductors and a tunable impedance circuit electrically connected to at least one of the mutually coupled inductors. The second tunable filter is coupled between an antenna switch and an antenna node. Related methods and wireless communication devices are also disclosed.

A radio frequency module (1) includes a first switch (4), an attenuation filter (3), and a plurality of band pass filters (12A to 12C, 22A to 22C). The first switch (4) is a switch that is capable of simultaneously connecting a common terminal (40) to selection terminals (41, 42) out of a plurality of selection terminals (41 to 43). The plurality of band pass filters (12A to 12C, 22A to 22C) include a first band pass filter (22A) and a second band pass filter (22B). The attenuation filter (3) includes at least one reactive element out of an inductive element and a capacitive element. In the radio frequency module (1), the reactive element is adjacent to at least one band pass filter out of the plurality of band pass filters (12A to 12C, 22A to 22C).