A filter circuit is provided which allows the pass band to be tuned to a desired communication signal while achieving increased attenuation in a given frequency band that lies outside the pass band. A filter circuit includes a fixed filter and a tunable filter. The fixed filter has a pass band wider than a frequency band corresponding to a predetermined communication signal and overlapping with the frequency band corresponding to the communication signal. The tunable filter has a stop band narrower than the pass band of the fixed filter and having tunable frequency. The fixed filter and the tunable filter are connected in series.

A method that incorporates teachings of the subject disclosure may include, for example, a method comprising receiving from a transceiver that is implemented as an integrated circuit (IC) chip, by a variable reactive element, a signal, wherein the signal is in a frequency band that comprises a first sub-frequency band and a second sub-frequency band, controlling, by a controller, the variable reactive element, such that the variable reactive element is placed into one of a group of states, wherein the group of states comprises a first state having a first reactance and a second state having a second reactance, and wherein the first reactance is different from the second reactance. Other embodiments are disclosed.

A radio-frequency module includes a multilayer substrate, an input switch, an output switch, and filters. A switch IC is disposed on a main surface of the multilayer substrate. The input switch is disposed in the switch IC and includes a first input terminal and first output terminals. The output switch is disposed in the switch IC and includes second input terminals and a second output terminal. The filters are disposed outside the switch IC and are connected to the first output terminals and the second input terminals. In a plan view of the multilayer substrate, the first input terminal and the first output terminals are disposed close to a first side of an exterior of the switch IC, and the second input terminals and the second output terminal are disposed close to a second side different from the first side of the exterior of the switch IC.

A switch module includes a switch circuit and a filter. The switch circuit includes two or more selection terminals, a common terminal provided for the two or more selection terminals, and first and second bypass terminals. The filter is connected between the first and second bypass terminals and reduces harmonics of a radio-frequency signal which passes through the filter. The switch circuit is selectively switched between a first connection mode and a second connection mode. In the first connection mode, the common terminal is connected to any of the two or more selection terminals. In the second connection mode, the common terminal is connected to the first bypass terminal and the second bypass terminal is connected to any of the two or more selection terminals.

A filter includes a series arm circuit connected between an input-output terminal and an input-output terminal and a parallel arm circuit connected between a ground and a node. The parallel arm circuit includes a first circuit and a second circuit. The first circuit has a parallel arm resonator. The second circuit is connected in parallel with the first circuit and has a parallel arm resonator. At least one of the first and second circuits includes a variable frequency circuit. The variable frequency circuit is connected in series with the parallel arm resonator or the parallel arm resonator included in the corresponding one of the first and second circuits. The variable frequency circuit has an impedance element and a switch connected in parallel with each other. The parallel arm resonator has a resonant frequency different from the parallel arm resonator and an anti-resonant frequency different from the parallel arm resonator.

A high-frequency filter includes a variable frequency filter, a fixed frequency filter, and switches. The variable frequency filter varies a passband in association with frequencies used in multiple communication band. The fixed frequency filter fixes a passband in association with a frequency used in a specific communication band different from the multiple communication bands. The switches are used to switch connection configuration to the variable frequency filter or the fixed frequency filter.

A radio-frequency module includes a multilayer substrate, an input switch, an output switch, and filters. A switch IC is disposed on a main surface of the multilayer substrate. The input switch is disposed in the switch IC and includes a first input terminal and first output terminals. The output switch is disposed in the switch IC and includes second input terminals and a second output terminal. The filters are disposed outside the switch IC and are connected to the first output terminals and the second input terminals. In a plan view of the multilayer substrate, the first input terminal and the first output terminals are disposed close to a first side of an exterior of the switch IC, and the second input terminals and the second output terminal are disposed close to a second side different from the first side of the exterior of the switch IC.

A radio frequency filter includes communication bandpass filters disposed corresponding respectively to a plurality of communication bands, a switch, and a matching circuit. The switch includes a common terminal and a plurality of optionally selectable terminals, the plurality of optionally selectable terminals being individually connected to the plurality of bandpass filters in a one-to-one relation. The matching circuit is connected to the common terminal and is a common matching circuit to the plurality of communication bandpass filters. The plurality of communication bandpass filters are set such that filter characteristics of a serial circuit in combination of one of the plurality of communication bandpass filters, the one being selected by the switch, and the common matching circuit are improved in comparison with filter characteristics of the selected communication bandpass filter with respect to the communication band corresponding to the selected communication bandpass filter.

A coil component includes a magnetic body having a plurality of filter parts disposed on a substrate and spaced apart from each other in a thickness direction. A plurality of input terminals and output terminals are disposed on outer surfaces of the magnetic body. Each of the filter parts includes upper and lower coils disposed in the magnetic body and spaced apart from each other in the thickness direction. In one example, a number of turns of the upper and lower coils of one filter part is different from a number of turns of the upper and lower coils of another filter part adjacent thereto. In another example, the number of turns of the upper and lower coils of the one and the other filter parts are the same, but capacitances of the one and the other filter parts are different.

A branching device (10) includes a switch (SW1), a fixed filter circuit (11), and a tunable filter (TF1). The switch (SW1) includes a common terminal (Ps11) and individual terminals (Ps12, Ps13). The fixed filter circuit (11) is connected to the individual terminal (Ps12) and has a fixed pass band. The tunable filter (TF1) is connected to the individual terminal (Ps13) and has a tunable pass band. The fixed filter circuit (11) includes filters (FIL1, FIL2) having different pass bands. The pass bands of the filters (FIL1, FIL2) correspond to frequency bands to be used in carrier aggregation.