Filter circuitry is used in communication systems that employ multiple antennas. In general, a communication system may have a transmit path and a receive path. The transmit path extends to a first antenna port and is configured to present signals for transmission in a first communication band and a second communication band to the first antenna port for transmission via a first antenna that is coupled to the first antenna port. The receive path extends to a second antenna port and comprises a first multiple passband/multiple stopband filter that provides a plurality of passbands and a plurality of stopbands interleaved with one another, wherein a first stopband and a second stopband of the plurality of stopbands correspond respectively to the first communication band and the second communication band and are separated by a first passband of the plurality of passbands.

Acoustic wave devices are disclosed. An acoustic wave device can include a first filter and a second filter coupled to a common node. The second filter includes acoustic wave resonators of a first type (e.g., bulk acoustic wave resonators) and a series acoustic wave resonator of the second type (e.g., a surface acoustic wave resonator) that is coupled between the acoustic wave resonators of the first type and the common node. The acoustic wave device can further include a loop circuit coupled to the first filter, in which the loop circuit is configured to generate an anti-phase signal to a target signal at a particular frequency. In certain embodiments, the first filter is a receive filter and the second filter is a transmit filter.

An extractor includes a band pass filter and a band elimination filter. One filter of the band pass filter and the band elimination filter includes at least one serial arm resonator and at least one parallel arm resonator that are each defined by an acoustic wave resonator. Any one of the at least one serial arm resonator and the at least one parallel arm resonator includes, among a divided resonator group divided resonator including a plurality of divided resonators coupled in series to each other, a first divided resonator group that is a largest in number of the divided resonators coupled in series and a smallest in capacitance.

Aspects of this disclosure relate to a hybrid acoustic LC filter cascaded with a non-acoustic LC filter. The hybrid acoustic filter can filter a radio frequency signal. The hybrid acoustic LC filter can include acoustic resonators, an inductor, and a capacitor. The inductor and capacitor can be external to an acoustic resonator die. The non-acoustic LC filter includes an LC circuit. Related multiplexers, wireless communication devices, and methods are disclosed.

A variable filter circuit includes a serial arm connected between ports (P1-P2), a parallel arm having a resonator connected in series between ports (P1-P3), and another parallel arm having another resonator connected in series between ports (P2-P3). The serial arm includes a capacitor connected between the ports (P1-P2), and the parallel arms include variable capacitances connected in series to the resonators.

Provided is a variable filter circuit that can control the bandwidth and center frequency of a pass band, can realize steep attenuation characteristics in bands close to the pass band, and enables the total number of variable reactance units to be reduced. A variable filter circuit includes an inductor (Ls1) and a capacitor (Cs1), which are connected in series between a first input/output terminal (P1) and a second input/output terminal (P2), and resonators (Re_p1, Re_p2, Re_p3, Re_p4) and variable capacitors (Cc1, Cc2, Cc3, Cc4), which are connected in series between two ends of the inductor (Ls1) and the capacitor (Cs1) and ground connection terminals.

An improved electro acoustic RF filter (FC) is provided. The RF filter comprises an electro acoustic resonator (EAR) connected between an input port and an output port, an impedance element and a damping and/or dissipation element (DE) in mechanical contact to the impedance element. The damping and/or dissipation element is provided and configured to remove acoustic energy from the impedance element which has a similar construction as the resonator on the same substrate. With such a construction an acoustically inactive impedance element (AIIE) is obtained.

A filter device having a pass band and a stop band on a lower frequency side than the pass band includes a filter having a pass band including the pass band, a series arm resonator connected in series to the filter, a first inductor directly connected in series to the series arm resonator, and a parallel arm resonator connected between a node on a path connecting the filter and the series arm resonator and the ground. The parallel arm resonator constitutes a resonance circuit having a resonant frequency at which an attenuation pole corresponding to a high frequency end of the first stop band, and the series arm resonator and the inductor constitute a resonance circuit having an anti-resonant frequency on a lower frequency side than the pass band and having a sub-resonant frequency higher than a resonant frequency of the resonance circuit.

Embodiments of the invention include a piezoelectric package integrated filtering device that includes a film stack. In one example, the film stack includes a first electrode, a piezoelectric material in contact with the first electrode, and a second electrode in contact with the piezoelectric material. The film stack is suspended with respect to a cavity of an organic substrate having organic material and the film stack generates an acoustic wave to be propagated across the film stack in response to an application of an electrical signal between the first and second electrodes.

A variable filter circuit includes a serial arm connected between ports (P1-P2), a parallel arm having a resonator connected in series between ports (P1-P3), and another parallel arm having another resonator connected in series between ports (P2-P3). The serial arm includes an inductor connected between the ports (P1-P2), and the parallel arms include variable capacitances connected in series to the resonators.