Abstract: 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.

Abstract: A filter module (20) includes a filter circuit (22) that includes switches (221SW and 224SW), a pass band of the filter circuit (22) being switched in accordance with switching between ON and OFF of the switches (221SW and 224SW); and an impedance matching circuit (21) that is disposed in at least one of a preceding stage and a subsequent stage of the filter circuit (22) and that includes a switch (212SW), an element value for achieving impedance matching being switched in the impedance matching circuit (21) in accordance with switching between ON and OFF of the switch (212SW). The switches (221SW and 224SW) and the switch (212SW) synchronize with each other regarding timing of switching between ON and OFF.

Abstract: A radio frequency filter circuit (22A) includes a series-arm resonator (22s), a parallel-arm resonator (22p1), a parallel-arm resonator (22p2) that is connected between a node x1 and a ground terminal, a switch (22SW) that is arranged between the node x1 and the ground terminal and switches between electrical connection and electrical non-connection of a path connecting the node x1, the parallel-arm resonator (22p2), and the ground terminal. The parallel-arm resonator (22p1) and a series circuit in which the parallel-arm resonator (22p2) and the switch (22SW) are connected in series are connected in parallel between the node x1 and the ground terminal. A resonant frequency (frp) of the parallel-arm resonator (22p1) is lower than a resonant frequency (frs) of the series-arm resonator (22s). A resonant frequency (frp2) of the parallel-arm resonator (22p2) is higher than the resonant frequency (frp) of the parallel-arm resonator (22p1).

Abstract: An impedance matching circuit (31) includes inductors (311L and 312L) that are connected in series, a switch (311S) that includes a first terminal connected to an end of the inductor (311L) and a second terminal and that switches between connection and disconnection between the first terminal and the second terminal, a switch (312S) that includes a third terminal connected to a connection point of the other end of the inductor (311L) and an end of the inductor (312L) and a fourth terminal and that switches between connection and disconnection between the third terminal and the fourth terminal, a switch (313S) that includes a fifth terminal connected to the other end of the inductor (312L) and a sixth terminal and that switches between connection and disconnection between the fifth terminal and the sixth terminal. The second terminal, the fourth terminal, and the sixth terminal are connected to each other.

Abstract: 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.

Abstract: A filter device includes first, second and third filter circuits that are connected to a common terminal. The first filter circuit includes a first inductor that is closest to the common terminal along a first signal line and a first capacitance element that is connected in parallel with the first inductor, the second filter circuit includes a series arm resonator, which is a second acoustic resonator, that is closest to the common terminal along a second signal line, and the third filter circuit includes a third acoustic resonator that is closest to the common terminal along a third signal line.

Abstract: An RF front-end circuit (2) includes an antenna common terminal (20) connected to an antenna element (1), an SPDT switch circuit (21) having a common terminal (21c) and select terminals (21s1 and 21s2), and four filter elements (22A to 22D). The common terminal (21c) and the filter elements (22C and 22D) are connected to the antenna common terminal (20). The filter elements (22A and 22B) are connected to the select terminals (21s1 and 21s2), respectively. Pass bands of the filter elements (22A, 22C and 22D) do not overlap with one another, and pass bands of the filter elements (22B, 22C and 22D) do not overlap with one another. The pass bands of the filter elements (22A and 22B) partly overlap with each other.

Abstract: A tunable filter includes a series-arm resonant circuit, and a parallel-arm resonant circuit. The series-arm resonant circuit includes a group of acoustic wave resonant circuits that have different resonant frequencies, a variable capacitor, and switching circuits. The parallel-arm resonant circuit includes another group of acoustic wave resonant circuits that have different resonant frequencies, a variable capacitor, and switching circuits. For example, the difference in pass-band frequency caused by the difference in resonant frequency between the acoustic wave resonant circuit in the group and the acoustic wave resonant circuit in the other group is greater than the maximum difference in pass-band frequency resulting from the variable range of capacitance of the variable capacitor.

Abstract: A filter device includes first, second and third filter circuits that are connected to a common terminal. The first filter circuit includes a first inductor that is closest to the common terminal along a first signal line and a first capacitance element that is connected in parallel with the first inductor, the second filter circuit includes a series arm resonator, which is a second acoustic resonator, that is closest to the common terminal along a second signal line, and the third filter circuit includes a third acoustic resonator that is closest to the common terminal along a third signal line.

Abstract: A filter apparatus includes a low pass filter and a high pass filter connected in series to each other. The low pass filter includes first acoustic resonators including a resonant frequency and an anti-resonant frequency, first inductors, and first capacitive elements. The high pass filter includes second inductors, second capacitive elements, and second acoustic resonators. A first attenuation band caused by the anti-resonant frequency of the first acoustic resonators is provided at a low frequency side of a pass band and a second attenuation band caused by the resonant frequency of the second acoustic resonators is provided at a high frequency side of the pass band. A third attenuation band caused by a first LC resonant circuit is provided at a low frequency side of the first attenuation band and a fourth attenuation band caused by a second LC resonant circuit is provided at a high frequency side of the second attenuation band.

Abstract: A multilayer filter includes a plurality of mutually coupled resonant circuits provided within a multilayer body. Capacitor internal electrodes, inductor internal electrodes, and inductor via electrodes, ground via electrodes, and input-output via electrodes are arranged within the multilayer body. The ground via electrodes and the input-output via electrodes are provided on a dielectric layer on a mounting surface, or a second dielectric layer on a first dielectric layer provided on the mounting surface. The capacitor internal electrodes arranged towards the side of the mounting surface do not overlap the input-output electrodes when viewed in plan view. With this configuration, degradation in frequency characteristics of a resonant circuit is effectively prevented by controlling one of an inductive component and a capacitive component of the resonant circuit.

Abstract: In a band pass filter, a first elastic wave resonator includes a first base board type and a first electrode configuration significantly improved or optimal for frequency characteristics of the first elastic wave resonator, and a second elastic wave resonator includes a second base board type and a second electrode configuration significantly improved or optimal for frequency characteristics of the second elastic wave resonator. A first attenuation pole provided by the first elastic wave resonator and a second attenuation pole provided by the second elastic wave resonator is steeper than if the first elastic wave resonator and the second elastic wave resonator that have different frequency characteristics include electrodes having the same configuration on the same types of base boards.

Abstract: A communication device is provided with a band elimination filter that has one end connected to an antenna terminal, and a first multiplexer that is connected to the other end of the band elimination filter. The band elimination filter is configured to eliminate signals of a frequency band that is different from the frequencies of signals transmitted and received in the first multiplexer, and is configured from a filter circuit that includes a bulk wave element.

Abstract: A filter device includes a first LC parallel resonance circuit having a first inductance and connected between a line connecting an input terminal and an output terminal and a ground potential, a second LC parallel resonance circuit having a second inductance and connected between the line and the ground potential, and at least one elastic wave resonator that is connected between an end portion of the first LC parallel resonance circuit and an end portion of the second LC parallel resonance circuit. Attenuation-frequency characteristics of an LC filter including the first LC parallel resonance circuit, the second LC parallel resonance circuit, and a capacitive property and attenuation-frequency characteristics of the at least one elastic wave resonator are used.

Abstract: A ladder filter includes a series arm resonator arranged on a series arm connecting an input terminal and an output terminal to each other, and at least one parallel arm resonator. The series arm resonator and the at least one parallel arm resonator are resonators each including a resonant point and an anti-resonant point. The series arm resonator includes first and second series arm resonators connected in parallel with each other. For a resonant frequency fr1 and an anti-resonant frequency fa1 of the first series arm resonator, and for a resonant frequency fr2 and an anti-resonant frequency fa2 of the second series arm resonator, resonant frequency difference ?fr=|fr1?fr2|>|fa2?fr1|.

Abstract: A filter apparatus includes a low pass filter and a high pass filter connected in series to each other. The low pass filter includes first acoustic resonators including a resonant frequency and an anti-resonant frequency, first inductors, and first capacitive elements. The high pass filter includes second inductors, second capacitive elements, and second acoustic resonators. A first attenuation band caused by the anti-resonant frequency of the first acoustic resonators is provided at a low frequency side of a pass band and a second attenuation band caused by the resonant frequency of the second acoustic resonators is provided at a high frequency side of the pass band. A third attenuation band caused by a first LC resonant circuit is provided at a low frequency side of the first attenuation band and a fourth attenuation band caused by a second LC resonant circuit is provided at a high frequency side of the second attenuation band.

Abstract: A filter device includes a first LC parallel resonance circuit having a first inductance and connected between a line connecting an input terminal and an output terminal and a ground potential, a second LC parallel resonance circuit having a second inductance and connected between the line and the ground potential, and at least one elastic wave resonator that is connected between an end portion of the first LC parallel resonance circuit and an end portion of the second LC parallel resonance circuit. Attenuation-frequency characteristics of an LC filter including the first LC parallel resonance circuit, the second LC parallel resonance circuit, and a capacitive property and attenuation-frequency characteristics of the at least one elastic wave resonator are used.

Abstract: A communication device is provided with a band elimination filter that has one end connected to an antenna terminal, and a first multiplexer that is connected to the other end of the band elimination filter. The band elimination filter is configured to eliminate signals of a frequency band that is different from the frequencies of signals transmitted and received in the first multiplexer, and is configured from a filter circuit that includes a bulk wave element.

Abstract: A multilayer filter includes a plurality of mutually coupled resonant circuits provided within a multilayer body. Capacitor internal electrodes, inductor internal electrodes, and inductor via electrodes, ground via electrodes, and input-output via electrodes are arranged within the multilayer body. The ground via electrodes and the input-output via electrodes are provided on a dielectric layer on a mounting surface, or a second dielectric layer on a first dielectric layer provided on the mounting surface. The capacitor internal electrodes arranged towards the side of the mounting surface do not overlap the input-output electrodes when viewed in plan view. With this configuration, degradation in frequency characteristics of a resonant circuit is effectively prevented by controlling one of an inductive component and a capacitive component of the resonant circuit.

Abstract: A multilayer filter includes a plurality of mutually coupled resonant circuits provided within a multilayer body. Capacitor internal electrodes, inductor internal electrodes, and inductor via electrodes, ground via electrodes, and input-output via electrodes are arranged within the multilayer body. The ground via electrodes and the input-output via electrodes are provided on a dielectric layer on a mounting surface, or a second dielectric layer on a first dielectric layer provided on the mounting surface. The capacitor internal electrodes arranged towards the side of the mounting surface do not overlap the input-output electrodes when viewed in plan view. With this configuration, degradation in frequency characteristics of a resonant circuit is effectively prevented by controlling one of an inductive component and a capacitive component of the resonant circuit.