Aspects of this disclosure relate to an acoustic wave resonator having at least two resonant frequencies. An acoustic wave filter can include series acoustic wave resonators and shunt acoustic wave resonators together arranged to filter a radio frequency signal. A first shunt resonator of the shunt acoustic wave resonators can include an interdigital transducer electrode and have at least a first resonant frequency and a second resonant frequency. Related acoustic wave resonators, multiplexers, wireless devices, and methods are disclosed.

A signal filter includes a notch filter and a wideband filter. The notch filter is configured to perform a band-rejection filtering operation according to a band-rejection filtering property. The wideband filter is coupled to the notch filter, and is configured to perform a wideband filtering operation according to a wideband filtering property. The band-rejection filtering property includes a first cutoff frequency, a frequency bandwidth, a relatively high quality factor and a relatively low coupling coefficient. The wideband filtering property includes a second cutoff frequency, a relatively low quality factor and a relatively high coupling coefficient. The first and the second cutoff frequencies have a frequency difference therebetween. A ratio of the frequency difference to the frequency bandwidth is within a preset ratio range being from 2.5% to 20%.

A notch filter includes a substrate having piezoelectricity, the substrate including a high-acoustic-velocity member, a low-acoustic-velocity film provided on the high-acoustic-velocity member, and a piezoelectric thin film provided on the low-acoustic-velocity film; an interdigital transducer electrode provided on the piezoelectric thin film; and reflectors provided on both sides of the interdigital transducer electrode in an acoustic wave propagation direction. An IR gap is within one of two ranges: 0.1λ≤G.sub.IR<0.5λ or 0.5λ<G.sub.IR≤0.9λ, where λ is a wavelength determined by an electrode finger pitch of the interdigital transducer electrode, and the IR gap is a distance between electrode finger centers of an electrode finger of the interdigital transducer electrode closest to the reflector out of the electrode fingers of the interdigital transducer electrode, and an electrode finger of the reflector closest to the interdigital transducer electrode, out of the electrode fingers of the reflector.

An extractor includes a band elimination filter that is connected between a common terminal and a first input-output terminal and that has a stop band equal or substantially equal to a first frequency band, and a band pass filter that is connected between the common terminal and a second input-output terminal and that has a pass band equal or substantially equal to a second frequency band that overlaps the first frequency band. The band pass filter includes, series arm resonators, three or more parallel arm resonators, and three or more inductors that are connected between the ground and the parallel arm resonators. The L value of a first inductor that is connected and nearest to the common terminal is smaller than the L value of a third inductor, and the L value of a second inductor that is connected and second-nearest to the common terminal is smaller than the L value of the third inductor.

A tunable filter using acoustic resonators is disclosed. A tunable filter includes a plurality of tunable resonator units (20). Each tunable resonator unit (20) has acoustic wave resonators (12). Each acoustic wave resonator is associated with a different tunable frequency. Each tunable resonator unit also has a first switch (22) configured to select one of the plurality of acoustic wave resonators of the tunable resonator unit at a time. The first switches of the plurality of tunable resonator units are coupled to cooperatively select one acoustic wave resonator in each one of the plurality of tunable resonator units, where a selected acoustic wave resonator in a tunable resonator unit of the plurality of tunable acoustic resonator units is associated with a same tunable frequency response as the other selected acoustic resonators of the others of the plurality of tunable acoustic resonator units. The selection results in an overall tunable frequency response.

A multiplexer includes: a first bandpass filter having a first end coupled to a common terminal and a second end coupled to a first terminal, the first bandpass filter having a first passband; a second bandpass filter having a first end coupled to the common terminal and a second end coupled to a second terminal, the second bandpass filter having a second passband that does not overlap with the first passband and is higher than the first passband; and a first band-stop filter having a first end coupled to the first terminal and a second end coupled to the second terminal, the first band-stop filter having a first stopband formed of a first attenuation pole and a second attenuation pole, the first attenuation pole being located within the first passband or near the first passband, the second attenuation pole being located within the second passband or near the second passband.

Aspects of this disclosure relate to an acoustic wave resonator having at least two resonant frequencies. An acoustic wave filter can include series acoustic wave resonators and shunt acoustic wave resonators together arranged to filter a radio frequency signal. A first shunt resonator of the shunt acoustic wave resonators can include an interdigital transducer electrode and have at least a first resonant frequency and a second resonant frequency. Related acoustic wave resonators, multiplexers, wireless devices, and methods are disclosed.

A filter circuit comprises in a signal line a band filter (BF) allowing to let pass a useful frequency band and a notch filter (NF) circuited in series to the band filter for filtering out a stop band frequency. The notch filter comprises a series circuit of a number of parallel shunt elements (SE1 . . . SE6) wherein each shunt element is shifted infrequency against the other shunt elements that the frequencies thereof are distributed (f1 . . . F6) over a notch band. All shunt elements may be realized as a SAW one-port resonator (TR.sub.NF) including regions with different pitches.

An extractor includes a band pass filter and a band elimination filter. In the band pass filter, an IDT electrode in at least one of a first series arm resonator and a first parallel arm resonator that are arranged at a series arm and a parallel arm, respectively, closest to a common terminal is a first IDT electrode in which neither a plurality of first electrode fingers nor a plurality of second electrode fingers is partially missing, and an IDT electrode in at least one of the first series arm resonator or the first parallel arm resonator that does not include the first IDT electrode, second series arm resonators, and second parallel arm resonators is a second IDT electrode in which at least one of a plurality of electrode fingers and a plurality of second electrode fingers is partially missing.

A wireless communication device includes a first transceiver operable according to a first radio technology and a second transceiver operable according to a second radio technology and operable concurrently with the first transceiver. The wireless communication device further includes an antenna configured to transmit radio transmissions of the second transceiver, and a filter circuit coupling the second transceiver with the antenna. The filter circuit includes a first frequency path and a second frequency path in parallel. The first frequency path passes a first set of frequencies of the radio transmissions and the second frequency path passes a second set of frequencies of the radio transmissions. One of the first frequency path or the second frequency path is configured to filter the radio transmissions of the second transceiver to remove signals corresponding to the one or more operating frequencies of the first transceiver from the radio transmissions of the second transceiver.