A frontend module includes a first filter having a passband of a first frequency band, a second filter having a passband of a second frequency band, the second frequency band being higher than the first frequency band, a third filter having a passband of a third frequency band, the third frequency band being higher than the second frequency band, and a sub-filter, connected to the second filter, configured to provide attenuation characteristics for the first frequency band, wherein the second filter comprises a plurality of parallel LC resonance circuits arranged between a ground and different nodes, from among a plurality of nodes between a first terminal and a second terminal, wherein an inductor is connected to a portion of the plurality of parallel LC resonance circuits.

An apparatus is disclosed for harmonic reduction with filtering. In example aspects, the apparatus includes a filter circuit with first and second filter ports, first and second lattice filters, and first and second signal manipulator circuits. The first signal manipulator circuit includes a first port, a second port, and a third port coupled to the first filter port. The first signal manipulator circuit splits an input signal into multiple split signals, shifts a phase thereof to produce at least one phase-shifted split signal, and provides the phase-shifted split signal to the first and second ports. The first lattice filter is coupled to the first port, and the second lattice filter is coupled to the second port. The second signal manipulator circuit includes a first port coupled to the first lattice filter, a second port coupled to the second lattice filter, and a third port coupled to the second filter port.

A common line is connected between a common terminal and a common connection node. A first filter has a first pass band. A second filter has a second pass band. At least one of a first condition and a second condition is satisfied. The first condition is that in the first pass band any one of a first impedance of the common line alone viewed from the common terminal (P10) and a second impedance of the first filter viewed from the common connection node includes an inductive property and the other includes a capacitive property. The second condition is that in the second pass band one of the first impedance and a third impedance of the second filter viewed from the common connection node includes an inductive property and the other includes a capacitive property.

A common line is connected between a common terminal and a common connection node. A first filter has a first pass band. A second filter has a second pass band. At least one of a first condition and a second condition is satisfied. The first condition is that in the first pass band any one of a first impedance of the common line alone viewed from the common terminal (P10) and a second impedance of the first filter viewed from the common connection node includes an inductive property and the other includes a capacitive property. The second condition is that in the second pass band one of the first impedance and a third impedance of the second filter viewed from the common connection node includes an inductive property and the other includes a capacitive property.

To achieve miniaturization. A matching circuit is connected to a connection terminal that is one of an input terminal and an output terminal of an amplifier. A mounting substrate has a ground layer. The matching circuit includes a main line, a sub-line, and an IC chip. The main line is formed of a first conductor pattern intersecting a thickness direction of the mounting substrate, and is connected to a connection terminal of the amplifier. The sub-line is formed of a second conductor pattern intersecting the thickness direction of the mounting substrate, and is connected between the main line and the ground layer. The sub-line is opposed to the main line in the thickness direction of the mounting substrate. The IC chip is disposed on the mounting substrate, and includes an adjustment unit that adjusts impedance conversion characteristics of the matching circuit.

A multiplexer includes filters and low pass filters. A second frequency band and a third frequency band are partially different. A first frequency band does not overlap the second frequency band and the third frequency band. One end of the filter is connected to a common terminal and the other end is connected to an input/output terminal. The low pass filter is connected in one end to the common terminal and in the other end to one end of the filter. The other end of the filter is connected to one end of the low pass filter. The other end of the low pass filter is connected to the input/output terminal. One end of the filter is connected to a node between the other end of the low pass filter and one end of the filter and the other end of the filter is connected to the input/output terminal.

A radio-frequency module includes a switch performing switching of the connection between a common terminal and a selection terminal, a reception filter having a reception band in a band A as a passband, a transmission filter that has a transmission band in a band B as a passband and has an output terminal connected to the selection terminal, a filter that has the transmission band in a band B as an attenuation band and has an input terminal connected to the selection terminal, a reception path which connects the selection terminal and an input terminal of the reception filter and on which the filter is disposed, a bypass path which connects the selection terminal and the input terminal of the reception filter and on which no filter is disposed, and a transmission path which connects the selection terminal and a transmission terminal and on which the transmission filter is disposed.

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.

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.

The present invention is a signal isolation device comprising: a first circulator; a second circulator connected to the first circulator; a first radio frequency switch connected to the second circulator; an adjustable radio frequency limiter connected to the first radio frequency switch; a low noise amplifier connected to the adjustable radio frequency limiter; a bandpass filter connected the low noise amplifier; a power splitter connected the bandpass filter; an attenuator connected to the power splitter; a second radio frequency switch connected to the power splitter; an active filter chain connected to the second radio frequency switch; a third circulator connected to the attenuator and the first circulator; a power detector connected to the third circulator; and a trigger generator connected to the power detector.