A multiplexer includes: a first chip that has a first filter and a resonator, the first filter being connected between a common terminal and a first terminal, a first end of the resonator being connected to the common terminal not via the first filter; and a second chip that has a second filter, the second filter being connected between a second end of the resonator and a second terminal and having a pass band lower than that of the first filter, a resonance frequency of the resonator being higher than the pass band of the second filter.

A circuit having a power amplifier port, an antenna port, and a ladder network coupled between the power amplifier and antenna ports is disclosed. The ladder network includes a proximal series acoustic resonator coupled to the power amplifier port, a distal series acoustic resonator coupled to the antenna port, and at least one series acoustic resonator coupled between the proximal series acoustic resonator and the distal series acoustic resonator. A first shunt acoustic resonator is coupled between a fixed voltage node and the proximal series acoustic resonator and the at least one series acoustic resonator. A second shunt acoustic resonator is coupled between the fixed voltage node and a second node to which the at least one series acoustic resonator is also coupled. A first inductor is coupled in parallel with the proximal series acoustic resonator to create notches below and above a passband of the ladder network.

A filter includes a series resonator or a longitudinally coupled resonator on a path connecting a first input-and-output terminal and a second input-and-output terminal, and parallel resonators each connected between the path and a ground. Among the parallel resonators, a second parallel resonator and a first parallel resonator are connected in parallel without another resonator being interposed therebetween. An IDT electrode of the first parallel resonator includes different electrode finger pitches. An average of all the electrode finger pitches of the IDT electrode of the first parallel resonator is larger than an average of all the electrode finger pitches of an IDT electrode of the second parallel resonator.

A filter includes: a piezoelectric substrate; one or more series resonators that are located on the piezoelectric substrate and are connected in series between an input terminal and an output terminal; at least one series resonator that is connected between a first node and a second node, is included in the one or more series resonators, and includes a reflector that is grounded, the first node and the second node being located between the input terminal and the output terminal; and a cancel line that is connected in parallel with the at least one series resonator between the first node and the second node, and cancels a signal outside a passband propagating through the at least one series resonator from the first node to the second node.

A multiplexer includes a filter (10) arranged between a common terminal and an input/output terminal (110) and configured to pass a radio frequency signal in a first frequency band, and a filter (20) arranged between the common terminal and an input/output terminal (120) and configured to pass a radio frequency signal in a second frequency band. The filter includes series arm circuits (31 and 32) connected in series, a series arm circuit (33) connected in parallel to the series arm circuit (32), and a parallel arm circuit. The series arm circuit (32) includes a series arm resonator that is an acoustic wave resonator. The series arm circuit (33) includes a switch arranged on a second path connecting nodes. In a CA mode, the switch is OFF. In a non-CA mode, the switch is ON.

A duplexer includes a transmission filter with a ladder circuit configuration and a reception filter including a ladder filter portion connected to an antenna terminal and a longitudinally coupled resonator-type surface acoustic wave filter. In the transmission filter, a coupling capacitor is connected between an end portion of an inductor nearer to parallel arm resonators and a wiring line connecting the series arm resonators of the ladder filter portion to each other in the reception filter.

In an elastic wave filter device, a first filter including a first pass band and a second filter including a second pass band are common-connected at a common connection point. The first filter includes, on the common connection point side, a serial arm resonator, a parallel arm resonator, or a longitudinally coupled resonator-type elastic wave filter, and generates a fundamental wave and a high-order mode. A resonant frequency of the high-order mode on a higher frequency side relative to the first pass band of the first filter is smaller than the second pass band. On the common connection point side, a serial arm resonator in which the resonant frequency is not the highest, a parallel arm resonator, or a longitudinally coupled resonator-type elastic wave filter, is disposed.

A surface acoustic wave filter is disclosed. The surface acoustic wave filter includes a substrate, and first and second surface acoustic wave filter structures disposed on first and second main surfaces of the substrate, respectively. The first surface acoustic wave filter structure includes a first piezoelectric layer a plurality of first surface acoustic wave resonators formed on a top surface of the first piezoelectric layer, and a first wiring layer connecting the first surface acoustic wave resonators to each other. The second surface acoustic wave filter structure includes a second piezoelectric layer, a plurality of second surface acoustic wave resonators formed on a bottom surface of the second piezoelectric layer, and a second wiring layer connecting the second surface acoustic wave resonators to each other. A plurality of through electrodes extends through the substrate, the first piezoelectric layer, and the second piezoelectric layer. A circuit including the first surface acoustic wave resonators and the first wiring layer on the top surface of the first piezoelectric layer forms at least one first radio frequency filter, and a circuit including the plurality of second surface acoustic wave resonators and the second wiring layer on the bottom surface of the second piezoelectric layer forms at least one second radio frequency filter. The at least one first radio frequency filter and the at least one second radio frequency filter belong to different frequency bands.

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.

A multiplexer device includes a single die, at least three acoustic filters and at least one antenna port arranged on the single die, and a shunt inductance connected between each of the at least one antenna port and ground. Each acoustic filter includes one of a transmit or receive filter corresponding to a predetermined radio frequency band. The at least one antenna port is connected to at least one antenna, respectively, where each of the at least one antenna port is further connected to at least one acoustic filter arranged on the single die, and is configured to pass RF signals corresponding to the predetermined RF band of the connected at least one acoustic filter. The shunt inductance provides impedance matching between each of the at least one antenna port and each of the at least one acoustic filter connect to the at least one antenna port.