A filter includes a series-arm resonator connected on a path connecting input/output terminals, and first and second parallel-arm resonators connected between the same node on the path and ground. A resonant frequency of the second parallel-arm resonator is higher than a resonant frequency of the first parallel-arm resonator, and an anti-resonant frequency of the second parallel-arm resonator is higher than an anti-resonant frequency of the first parallel-arm resonator. Each of the first and second parallel-arm resonators includes an acoustic wave resonator including an IDT electrode. The IDT electrode in the second parallel-arm resonator has a higher duty ratio than the IDT electrode in the first parallel-arm resonator, where the duty ratio is the ratio of the width to the pitch of electrode fingers.

A filter device includes a filter (22A) connected to a common terminal (110) and having a first characteristic, a variable filter (22B) connected to the common terminal (110) and capable of changing a characteristic to one of a second characteristic and a third characteristic, and a switch (23). In the second characteristic, a second pass band including an overlapping band in which the second pass band and an attenuation band of the filter (22A) partially overlap in frequency is defined. Insertion loss within the overlapping band for the third characteristic is greater than insertion loss within the overlapping band for the second characteristic. When the filter (22A) is selected by the switch (23), the characteristic of the variable filter (22B) is set to the third characteristic.

A filter device includes a first ladder filter including serial resonators disposed in a terminal-to-terminal path and parallel resonators disposed in connection paths, a first acoustic wave resonator disposed in parallel to the parallel resonator, and a second acoustic wave resonator disposed in parallel to the serial resonator. Resonance points and anti-resonance points of the first and second acoustic wave resonators are both positioned on the lower frequency side or the higher frequency side of a pass band of the first ladder filter, and on the same side of the pass band of the first ladder filter, when viewed from the pass band of the first filter.

A filter circuit has a first resistor which is connected between an input node and an output node, a second resistor which is connected between the output node and a reference potential node, a first capacitor and a second capacitor which are connected in series between the input node and the output node, and a variable capacity part which is connected between a connection node of the first capacitor and the second capacitor and the reference potential node.

Electromagnetic coupler systems including built-in frequency detection, and modules and devices including such. One example of an electromagnetic coupler system includes an electromagnetic coupler having an input port, an output port, a coupled port, and an isolation port, the electromagnetic coupler including a main line extending between the input port and the output port, and a coupled line extending between the coupled port and the isolation port, the electromagnetic coupler being configured to produce a coupled signal at the coupled port responsive to receiving an input signal at the input port. An adjustable termination impedance is connected to the isolation port. A frequency detector is connected to the adjustable termination impedance and to the coupled port, and configured to detect a frequency of the coupled signal and provide an impedance control signal to tune the adjustable termination impedance based on the frequency of the coupled signal.

A filter circuit that secures the steepness from a pass range to an attenuation range while maintaining a wide-band transmission characteristic and a filter device including this filter circuit are formed. A filter circuit includes a first filter and a second filter. The first filter is a filter including an LC circuit in which a first frequency band is a pass band and a frequency band not higher than the first frequency band is an attenuation band. The second filter is a filter that attenuates a second frequency band within the first frequency band by using an attenuation pole produced by a resonance or an antiresonance of an acoustic wave resonator. Further, the first filter is placed closer to an antenna terminal than the second filter.

A flexible multi-path RF adaptive tuning network switch architecture that counteracts impedance mismatch conditions arising from various combinations of coupled RF band filters, particularly in a Carrier Aggregation-based (CA) radio system. In one version, a digitally-controlled tunable matching network is coupled to a multi-path RF switch in order to provide adaptive impedance matching for various combinations of RF band filters. Optionally, some or all RF band filters include an associated digitally-controlled filter pre-match network to further improve impedance matching. In a second version, some or all RF band filters coupled to a multi-path RF switch include a digitally-controlled phase matching network to provide necessary per-band impedance matching. Optionally, a digitally-controlled tunable matching network may be included on the common port of the multi-path RF switch to provide additional impedance matching capability. In a third version, CA direct mapped adaptive tuning networks include filter tuning blocks for selected lower frequency bands.

An electronic circuit includes a first filter and a second filter. The first filter passes a first frequency component of a first harmonic frequency generated by a first voltage source to form a potential difference in a chamber and a second frequency component of a second harmonic frequency higher than the first harmonic frequency. The second filter removes the first frequency component and the second frequency component received from the first filter. The second harmonic frequency is included in a first frequency band determined based on a capacitance of the second filter.

A multilayer filter may include a signal path having an input, an output, and a conductive layer overlying at least one of a plurality of dielectric layers. The conductive layer may be elongated in the first direction and may have a first edge aligned with the first direction and a second edge parallel with the first edge. The conductive layer may include a protrusion extending in the second direction and having an end edge that is parallel with the first edge and offset from the first edge in the second direction by a protrusion length that is greater than about 50 microns. The multilayer filter may include an inductor that is electrically connected at a first location with the signal path and electrically connected at a second location with at least one of the signal path or a ground.

A filter device includes: a common terminal; a first input/output terminal; a second input/output terminal; a first filter connected to a first path that connects the common terminal and the first input/output terminal, and having a passband that is a first band; a second filter connected to a second path that connects the common terminal and the second input/output terminal, and having a passband that is a second band having a frequency range that is different from and does not overlap a frequency range of the first band; a first switch element connected between a first node on the first path between the first filter and the first input/output terminal and a second node on the second path between the second filter and the second input/output terminal; and a second switch element on the second path, which is connected between the second node and the second input/output terminal.