A BAW device comprises a first BAW resonator (1) and a second BAW resonator (2). The first BAW resonator and the second BAW resonator each comprise a first electrode (11, 21), a second electrode (12, 22) and a piezoelectric layer (13, 23) being arranged in each case between the first electrode and the second electrode of the associated BAW resonator. The first electrodes, the second electrodes and the piezoelectric layers of both BAW resonators are designed essentially identically. A first conductor track (24) extends from the first electrode of the second BAW resonator to a third electric element (3) of the BAW device and electrically connects said first electrode with said third electric element. A first dummy conductor track (14) extends from the first electrode of the first BAW resonator, is electrically connected to said first electrode and, apart from said first electrode, is not electrically connected to any further electric element. The first dummy conductor track is designed such that it influences the acoustic and capacitive properties of the first BAW resonator essentially in the same way as the first conductor track influences the acoustic and capacitive properties of the second BAW resonator.

Packaged RF front end systems including a hybrid filter and an active circuit in a single package are described. In an example, a package includes an active die comprising an acoustic wave resonator. A package substrate is electrically coupled to the active die. A seal frame surrounds the acoustic wave resonator and is attached to the active die and to the package substrate, the seal frame hermetically sealing the acoustic wave resonator in a cavity between the active die and the package substrate.

A filter device includes first and second filters respectively having first and second passbands, the second passband being in a frequency range higher than the first passband. The first and second filters are commonly connected to a common terminal. In the first filter, multiple parallel arm resonators define a parallel connection unit in which the parallel arm resonators are connected in parallel with no serial arm resonators interposed therebetween. The parallel arm resonators in the parallel connection unit include first and second parallel arm resonators having anti-resonant frequencies different from each other. In combined impedance-frequency characteristics of the parallel arm resonators in the parallel connection unit, at least one anti-resonant frequency other than a highest anti-resonant frequency is equal to or higher than 2f.sub.1min−f.sub.2min and equal to or lower than 2f.sub.1max−f.sub.2max.

An acoustic wave device includes a first acoustic wave element including a first substrate having piezoelectricity at least in a portion thereof, a first functional electrode provided on a first surface of the first substrate, and a first wiring conductor electrically connected to the first functional electrode. The first acoustic wave element further includes a relay electrode on the first surface of the first substrate and electrically connected to a second wiring conductor, and a ground electrode on the first surface of the first substrate and electrically connected to the first functional electrode. The ground electrode is between at least one of the first functional electrode and the first wiring conductor, and the relay electrode, and is electrically insulated from the relay electrode.

A bulk acoustic resonator includes: a substrate including an upper surface on which a substrate protection layer is disposed; and a membrane layer forming a cavity together with the substrate, wherein a thickness deviation of either one or both of the substrate protection layer and the membrane layer is 170 Å or less.

A variable filter circuit includes: a series arm connected in series between a signal input terminal and a signal output terminal; a parallel arm connected between the series arm and a ground terminal that has a resonator; and a variable reactance portion in the parallel arm, and the resonator of a parallel arm at an initial stage connected to the signal input terminal that has a resonant frequency fr and an anti-resonant frequency fa that satisfy 100×(fn−fr)/(fa−fr)≦23.9(%) for communication bands for each of which a stop band is set so as to be close to a high-frequency side of a pass band, among the plurality of communication bands, where a resonant frequency is fr, an anti-resonant frequency is fa, and a cutoff frequency at a high-frequency side of a pass band of each communication band is fn.

An acoustic wave filter device includes a piezoelectric layer, a high-acoustic-velocity member, a low-acoustic-velocity film between the high-acoustic-velocity member and the piezoelectric layer, and first and second IDT electrodes on the piezoelectric layer to define acoustic wave resonators. An acoustic wave resonator of a series-arm resonator portion closest to an antenna end and/or an acoustic wave resonator of a parallel-arm resonator portion closest to the antenna end includes the first IDT electrode including first and second electrode fingers, and the remaining acoustic wave resonators include the second IDT electrode including third and fourth electrode fingers. In the first IDT electrode, a central area, first and second low-acoustic-velocity areas, and first and second high-acoustic-velocity areas extend along a direction perpendicular or substantially perpendicular to an acoustic wave propagating direction. First and second envelopes connecting the tips of the third and fourth electrode fingers of the second IDT electrode are inclined.

A filter using bulk acoustic wave resonators (BAWRs) is provided including BAWRs connected in series or in parallel to each other. A BAWR set is configured by connecting an inductance and capacitance (L/C) element to each BAWR in series or in parallel.

The specification relates to an RF filter in which characteristic filter variables have a decreased dependency on tuning. A filter in this case comprises series-interconnected basic elements that each have an electroacoustic resonator and impedance converters interconnected in series between the basic elements.

A filter circuit includes: a variable filter that is connected between a common terminal and a node and configured to change a passband thereof; a receive switch connected between a receive terminal, from which a reception signal in a first band is output, and the node; and a transmit switch connected between a transmit terminal, to which a transmission signal in a second band different from the first band is input, and the node.