Abstract: A filter includes: one or more series resonators that are connected in series between an input terminal and an output terminal; one or more parallel resonators that are connected in parallel between the input terminal and the output terminal; and a laterally coupled resonator that is connected in parallel with at least one of the one or more series resonators.

Abstract: A high-frequency filter including first and second signal terminals, a filter circuit having a passband and a stopband and being connected between the first signal terminal and the second signal terminal, and an additional circuit connected in parallel with the filter circuit between the first signal terminal and the second signal terminal. The filter circuit is configured to provide a first output signal responsive to receipt of an input signal. The additional circuit has an attenuation band within the stopband, and is configured to provide a second output signal responsive to receiving the input signal, the first and second output signals having phase components opposite to each other in the attenuation band.

Abstract: A device includes a base substrate (700) with a micro component (702) attached thereto. Suitably it is provided with routing elements (704) for conducting signals to and from the component (702). It also includes spacer members (706) which also can act as conducting structures for routing signals vertically. There is a capping structure (708) of a glass material, provided above the base substrate (700), bonded via the spacer members (706), preferably by eutectic bonding, wherein the capping structure (708) includes vias (710) including metal for providing electrical connection through the capping structure. The vias can be made by a stamping/pressing method entailing pressing needles under heating to soften the glass and applying pressure, to a predetermined depth in the glass. However, other methods are possible, e-g- drilling, etching, blasting.

Abstract: RF circuitry, which includes a first acoustic RF resonator (ARFR), a first compensating ARFR, and a second compensating ARFR, is disclosed. The first compensating ARFR is coupled between a first inductive element and a first end of the first ARFR. The second compensating ARFR is coupled between a second inductive element and a second end of the first ARFR. The first inductive element and the second inductive element are negatively coupled to one another. The first compensating ARFR, the second compensating ARFR, the first inductive element, and the second inductive element at least partially compensate for a parallel capacitance of the first ARFR.

Abstract: A glass wafer assembly is disclosed. In one aspect, the glass wafer assembly comprises a first glass wafer and a second glass wafer that are bonded by a conductive sealing ring. The conductive sealing ring defines a substantially hermetically sealed cavity between the first glass wafer and the second glass wafer. In another aspect, the first glass wafer and the second glass wafer each comprise a plurality of conductive through glass vias (TGVs). At least one active device is disposed in the substantially hermetically sealed cavity and can be electrically coupled to a conductive TGV in the first glass wafer and a conductive TGV in the second glass wafer to enable flexible electrical routing through the glass wafer assembly without wire bonding and over molding. As a result, it is possible to reduce footprint and height while improving radio frequency (RF) performance of the glass wafer assembly.

Abstract: An elastic wave filter includes a transmission circuit provided on a first main surface of a first piezoelectric substrate and a reception circuit provided on a second main surface of a second piezoelectric substrate. A mounting board on which the elastic wave filter is mounted includes a first ground electrode opposed to the transmission circuit; a first rear surface ground electrode overlapped with the transmission circuit in plan view of a rear surface; a second ground electrode opposed to the reception circuit; a second rear surface ground electrode overlapped with the reception circuit in plan view of the rear surface; a line electrode used for connection between the first ground electrode and the second ground electrode; and a first via electrode and a second via electrode passing through the mounting board. An amount of heat transfer per unit time of the second via electrode is greater than an amount of heat transfer per unit time of the first via electrode.

Abstract: A multiplexer includes: a first filter connected between a common terminal and a first terminal; a second filter connected between the common terminal and a second terminal, and having a passband lower in frequency than a passband of the first filter; and a resonant circuit including: a first inductor and a capacitor connected in series between a first end and a second end of the resonant circuit, the first end being coupled to a node at which the common terminal diverges into the first filter and the second filter, the second end being coupled to the first filter, and a second inductor connected in parallel to the first inductor and the capacitor between the first end and the second end, wherein the passband of the first filter is higher in frequency than an antiresonant frequency of the resonant circuit.

Abstract: A method of designing an acoustic microwave filter in accordance with frequency response requirements comprises generating a modeled filter circuit design having a plurality of circuit elements comprising an acoustic resonant element defined by an electrical circuit model that comprises a parallel static branch, a parallel motional branch, and one or both of a parallel Bragg Band branch that models an upper Bragg Band discontinuity and a parallel bulk mode function that models an acoustic bulk mode loss. The method further comprises optimizing the modeled filter circuit design to generate an optimized filter circuit design, comparing a frequency response of the optimized filter circuit design to the frequency response requirements, and constructing the acoustic microwave filter from the optimized filter circuit design based on the comparison.

Abstract: A mobile wireless communications device may include a portable housing including at least one electrically conductive housing portion configured to function as an antenna. The mobile wireless communications device may also include a printed circuit board (PCB) carried by the portable housing, and wireless transceiver circuitry carried by the PCB and including at least one circuit element carried by the PCB. The mobile wireless communications device may also include at least one current shunt component coupled between the at least one electrically conductive housing portion and the at least one circuit element.

Abstract: An acoustic wave device includes a first longitudinally-coupled acoustic wave filter having interdigital transducer (“IDT”) electrodes arranged in a propagation direction of acoustic wave, and a second longitudinally-coupled acoustic wave filter having IDT electrodes arranged in a propagation direction of acoustic wave. In the IDT electrodes of the first longitudinally-coupled acoustic wave filter, a comb-shaped electrode connected to an input port and another comb-shaped electrode connected to an output port are disposed in an in-phase relation. In the IDT electrodes of the second longitudinally-coupled acoustic wave filter, a comb-shaped electrode connected to an input port and another comb-shaped electrode connected to an output port are disposed in an anti-phase relation. This acoustic wave device has an excellent attenuation characteristic while maintaining a preferable insertion loss.

Abstract: A high-frequency module includes a filter unit and first and second external connection terminals. The filter unit includes first and second terminals and a plurality of SAW resonators. The plurality of SAW resonators are connected to one another by connection conductors. A matching element is connected between the first terminal and the first external connection terminal, and a matching element is connected between the second terminal and the second external connection terminal. At least one of the matching elements is inductively coupled or capacitively coupled to at least one of the connection conductors located at a position such that at least one of the SAW resonators is interposed between the matching element and the connection conductor.

Abstract: A filter includes: one or more series resonators connected in series between an input terminal and an output terminal; one or more parallel resonators connected in parallel between the input terminal and the output terminal; a first inductor having one end connected to at least one of the input terminal and the output terminal; a second inductor having one end connected to a terminal near a ground of at least one of the parallel resonators; and a third inductor connected between a first node and the ground, the first node connecting the other end of the first inductor and the other end of the second inductor.

Abstract: A filter circuit providing improved attenuation, a filter having improved attenuation and a duplexer with improved isolation are provided. The filter circuit has a first and a second coupling conductor segment which couple an input port to a ground port or the filter's output port. The filter circuit can be realized in the filter. The duplexer can comprise the filter, especially as its transmission filter.

Abstract: An RF component can have a reduced electromagnetic internal coupling and may be suitable for miniaturization as a result. The component includes a micro acoustic filter of ladder-type design in a housing and a double coil having a first coil segment and a second coil segment. The two coil segments are oriented in opposite directions. The two coil segments are arranged without crossover in one layer and the double coil is arranged in proximity to a parallel branch resonator of the ladder-type filter structure.

Abstract: A module includes: a duplexer including an antenna terminal; a first wiring connecting the antenna terminal to an antenna; a second wiring coupled to the antenna terminal without the first wiring; and an inductor coupled to the second wiring.

Abstract: A ladder surface acoustic wave filter includes a series arm connecting an input terminal and an output terminal, at least one parallel arm connecting the series arm and a ground terminal, at least one series arm resonator provided in the series arm, and at least two parallel arm resonators provided in at least one parallel arm and connected to each other in series. In the ladder surface acoustic wave filter, a connection point between at least the two parallel resonators connected to each other in series is grounded through an inductor.

Abstract: A method of designing an acoustic microwave filter in accordance with frequency response requirements comprises generating a modeled filter circuit design having a plurality of circuit elements comprising an acoustic resonant element defined by an electrical circuit model that comprises a parallel static branch, a parallel motional branch, and one or both of a parallel Bragg Band branch that models an upper Bragg Band discontinuity and a parallel bulk mode function that models an acoustic bulk mode loss. The method further comprises optimizing the modeled filter circuit design to generate an optimized filter circuit design, comparing a frequency response of the optimized filter circuit design to the frequency response requirements, and constructing the acoustic microwave filter from the optimized filter circuit design based on the comparison.

Abstract: A communication device is provided with a band elimination filter that has one end connected to an antenna terminal, and a first multiplexer that is connected to the other end of the band elimination filter. The band elimination filter is configured to eliminate signals of a frequency band that is different from the frequencies of signals transmitted and received in the first multiplexer, and is configured from a filter circuit that includes a bulk wave element.

Abstract: In an elastic wave device, a first electrode structure and a second electrode structure are provided on a piezoelectric substrate. The first electrode structure and the second electrode structure define first and second elastic wave element portions, respectively. A support frame on the piezoelectric substrate surrounds the first elastic wave element portion and the second elastic wave element portion. The support frame includes a dividing wall portion that divides the first elastic wave element portion and the second elastic wave element portion. A conductive shield electrode is provided in a groove provided in the dividing wall portion.

Abstract: An electronic device includes a main circuit connected between an input terminal and an output terminal, and an auxiliary circuit connected in parallel to the main circuit between the input terminal and the output terminal. The main circuit includes a filter having a first passband and a stopband. The auxiliary circuit has a passing characteristic that allows a signal having a frequency in a certain frequency band inside the stopband to pass through the auxiliary circuit. The main circuit is configured to output a main signal in response to an input signal. The auxiliary circuit is configured to output an auxiliary signal in response to the input signal. The main signal and the auxiliary signal contain phase components opposite to each other in the certain frequency band inside the stopband. This electronic device has an attenuation amount in the stopband.

Abstract: A first coil element includes a first loop-shaped conductor and a second loop-shaped conductor. A second coil element includes a third loop-shaped conductor and a fourth loop-shaped conductor. The first loop-shaped conductor and the second loop-shaped conductor are sandwiched in a stacking direction between the third loop-shaped conductor and the fourth loop-shaped conductor. A conductive pattern which is a portion of the first loop-shaped conductor and a conductive pattern which is a portion of the second loop-shaped conductor are connected in parallel. Then, each of a conductive pattern which is a remaining portion of the first loop-shaped conductor and a conductive pattern which is a remaining portion of the second loop-shaped conductor is connected in series with the parallel circuit.

Abstract: Provided is a bulk acoustic resonator (BAR)-based resonant structure in relation to electric and radio technologies, and more particularly, to a wireless power transmission system. A resonant apparatus for wireless power transmission may include a conducting loop, and a high quality capacitor. The high quality capacitor may include a metacapacitor including a thin piezoelectric layer disposed between two metal electrodes. The metacapacitor may be disposed between two dielectric layers of which central portions are etched, and the conducting loop may be disposed on an upper layer of the two dielectric layers.

Abstract: A filter unit of a high-frequency module includes SAW resonators connected in series with first and second series connection terminals therebetween, first and second shunt connection terminals, and additional SAW resonators. One end of one SAW resonator is connected to a connection node of other SAW resonators via a connection conductor, and the other end of the one SAW resonator is connected to the first shunt connection terminal via a connection conductor. The first shunt connection terminal is connected to ground via an inductor. A matching element is connected between the second series connection terminal and the second external connection terminal. The matching element is inductively coupled or capacitively coupled to the connection conductor.

Abstract: Disclosed are systems and methods for improving isolation between transmit and receive radio-frequency (RF) signals. In some embodiments, a system can be implemented for isolating RF signals during Tx and Rx operations. The system can include a Tx path and an Rx path, with the Tx path having a filter. In some embodiments, the Tx path can include a power amplifier having a plurality of interstages and an output stage, and the filter can be implemented at one of the interstages and before the output stage. The system can further include first and second antennas connected respectively to the Tx and Rx paths. The Tx path, the Rx path, and/or the first and second antennas can be configured to yield a desired level of isolation between the RF signal in the Tx and Tx paths.

Abstract: A surface acoustic wave filter includes a piezoelectric substrate, a lower-layer wiring line, an upper-layer wiring line, and an interlayer insulating film. The lower-layer wiring line is disposed on the piezoelectric substrate. The upper-layer wiring line crosses the lower-layer wiring line. The upper-layer wiring line has a potential that is different from the potential of the lower-layer wiring line. The interlayer insulating film is disposed between the lower-layer wiring line and the upper-layer wiring line. The interlayer insulating film has a portion that has a width that is not greater than the width of the upper-layer wiring line in a cross-sectional view taken along a direction in which the lower-layer wiring line extends.

Abstract: A vibrator element includes a base portion, a vibrating arm extending from the base portion, a first electrode provided on the vibrating arm, a second electrode provided above the first electrode, a piezoelectric body arranged between the first electrode and the second electrode, and an insulating film arranged between the first electrode and the piezoelectric body, in which the material of the first electrode contains TiN, the material of the insulating film contains SiO2, and the material of the piezoelectric body contains AlN.

Abstract: An elastic wave splitter includes an antenna terminal, a transmission terminal and reception terminals. A transmission filter is connected between the antenna terminal and the transmission terminal. A reception filter is connected between the antenna terminal and the reception terminals. The transmission filter and the reception filter are each defined by an elastic wave filter. A resonant circuit is connected between the antenna terminal and a ground potential. The resonant circuit includes a surface acoustic wave resonator and a capacitor connected in series with the surface acoustic wave resonator. A resonant frequency of the resonant circuit is positioned in a frequency band of an interference wave that causes intermodulation distortion to be generated.

Abstract: An acoustic filter includes a signal input port, a ladder-type filter, a first branch ladder-type filter, a second branch ladder-type filter, and a signal output port. The first branch ladder-type filter and the second branch ladder-type filter are connected in parallel to each other. The signal input port is connected to the ladder-type filter. The ladder-type filter circuit is connected in series to the first branch ladder-type filter and the second branch ladder-type filter. The first branch ladder-type filter circuit and the second branch ladder-type filter are connected to the signal output port.

Abstract: In an elastic wave filter device, an elastic wave filter element chip is mounted on a board. In the elastic wave filter element chip, a ladder filter including a plurality of series arm resonators and a plurality of parallel arm resonators are provided. In/on the board, a first inductor connected in parallel to the series arm resonator and a second inductor connected between the parallel arm resonators P1-P3 and a ground potential are provided. In/on the board, a shield electrode is located between the first inductor and the second inductor.

Abstract: An RF front end arrangement comprises first filtering, second filtering, third filtering, fourth filtering and a switching arrangement. The switching arrangement is configured to selectively connect the filtering to plural antennas such that at a particular time the first and third filtering is connected to a first antenna and the second and fourth filtering is connected to a second antenna. This allows filtering with different frequency response characteristics to be in use simultaneously for the same frequency band. This can reduce the insertion loss associated with a signal path.

Abstract: An acoustic wave device includes a piezoelectric substrate made of a lithium niobate material having the Euler angles (?, ?, ?), an electrode disposed on the piezoelectric substrate for exciting a major acoustic wave of a wavelength ?, and a protective layer disposed on the piezoelectric substrate to cover the electrode. The protective layer has a thickness greater than 0.27?. The Euler angles satisfy ?100°????60°; 1.193??2°???1.193?+2°; and either ???2??3° or ?2?+3°??.

Abstract: Exemplary embodiments are related to a low-noise amplifier (LNA) matching device. A device may include an antenna for receiving a wireless signal and at least one LNA. The device may further include an LNA matching device coupled between the antenna and the at least one LNA and configured to receive one or more control signals to provide an optimal LNA match setting for each band of a plurality of frequency bands.

Abstract: An antenna duplexer has a first filter passing a signal in a first frequency band and a second filter passing a signal in a second frequency band which is higher than the first frequency band. The first filter includes a first series resonator having a lowest antiresonance frequency and second series resonators. A propagation angle of a main elastic wave of the first series resonator a propagation angle of a main elastic wave of each of the second series resonators are different from each other so that an electromechanical coupling coefficient of the first series resonator is smaller than an electromechanical coupling coefficient of the second series resonators.

Abstract: A filter device includes a band pass filter connected between a first signal terminal and a second signal terminal and an LC circuit connected in parallel with the band pass filter. The LC circuit has anti-resonant characteristics that make the LC circuit be open at a pass band of the band pass filter, and make attenuation in a specified frequency band outside of the pass band of the band pass filter higher than in a case in which the LC circuit is not connected, as a result of the LC circuit being connected.

Abstract: A SAW device (1) comprises a substrate (3); SAW elements (10) on a first main surface (3a) of the substrate (3); first lines (intermediate lines (29) and output side lines (31)) that are disposed upon the first main face (3a) and connected to the SAW elements (10); an insulator (21) that is layered upon the first lines; second lines (a second ground line (33b) and a third ground line (33c)) that are layered upon the insulator (21) and configure three-dimensional wiring parts (39) with the first lines; and a cover (5) that seals the SAW elements (10) and the three-dimensional wiring parts (39). Wiring spaces (53), formed between the first main face (3a) and the cover (5), houses the three-dimensional wiring parts (39), without housing the SAW elements (10).

Abstract: A multiplexer device includes at least one filtering device having at least one first band pass filter, connected to a common port via at least one series inductance, respectively, and only one or non-overlapping passbands, and at least one second filtering device, each of which includes at least one second band pass filter with a total of at least two second band pass filters are connected to the common port and having non-overlapping passbands, respectively. Combined series inductance transformed input impedance of the at least one first filtering device is inductive, when viewed from the common port, in the passbands of the at least two second band pass filters. Combined input impedance of the at least one second filtering device is substantially capacitive, when viewed from the common port, in a passband of the at least one first band pass filter in the at least one first filtering device.

Abstract: An acoustic wave filter includes a piezoelectric substrate, an insulating pattern that has higher thermal conductivity than the piezoelectric substrate formed on the piezoelectric substrate, at least two pads formed on the piezoelectric substrate or the insulating pattern, at least one pad formed on the insulating pattern, at least one acoustic resonator formed on the insulating pattern, and at least one acoustic resonator directly formed on the piezoelectric substrate.

Abstract: The present invention relates to a circuit assembly which comprises an antenna path (A1), which can be connected to a first antenna (ANT1), a transmission path (TX1), a reception path (RX1), a duplexer (DPX1), operating with acoustic waves, which connects the transmission and reception paths (TX1, RX1) in each case to the antenna path (A1), and means for suppressing an interference signal.

Abstract: An apparatus and method for filtering a signal is described. The apparatus includes a first singly terminated filter that filters a signal in a first frequency range, and a second singly terminated filter that filters the signal in a second frequency range, the inputs of the filters being connected together, wherein an element of the first filter is coupled to an additional element to form a frequency response transmission zero in a stopband frequency range of the first filter. The method includes receiving a signal, the signal containing content from a first source in a first frequency range and content from a second source in a second frequency range different than the first range, applying filtering, and applying filtering to generate a second output signal, using filters that include a singly terminated filter section with additional circuit elements to form a transmission frequency zero in the stopband frequency range.

Abstract: An acoustic wave sensor includes a piezoelectric substrate, a transmitting electrode configured to excite a main acoustic wave propagating through a propagation region of an upper surface of the piezoelectric substrate, a receiving electrode configured to receive the propagated main acoustic wave, a first insulating film provided on the propagation region of the upper surface of the piezoelectric substrate, a second insulating film provided on the upper surface of the piezoelectric substrate to cover the first insulating film, and a reaction section provided on the upper surface of the second insulating film above the propagation region. The reaction section is configured to react with an object. A velocity of a transverse wave propagating through the first insulating film is higher than a velocity of a transverse wave propagating through the second insulating film. The acoustic wave sensor described above has high detection sensitivity.

Abstract: A high-frequency module includes a multilayer body including stacked dielectric and a pair of ground electrodes spaced apart from each other; a common terminal arranged in the multilayer body to receive and transmit communication signals; and a duplexer that is mounted on a surface of the multilayer body and that separates communication signals input and output via the common terminal. The duplexer includes a first SAW filter mounted on the surface of the multilayer body and grounded by the ground electrode and a second SAW filter mounted on the surface of the multilayer body so as to be spaced apart from the first SAW filter and is grounded by the ground electrode. Thus, degradation of isolation characteristics of the transmission and reception terminals of a splitter is prevented.

Abstract: Embodiments of resonator circuits and modulating resonators and are described generally herein. One or more acoustic wave resonators may be coupled in series or parallel to generate tunable filters. One or more acoustic wave resonances may be modulated by one or more capacitors or tunable capacitors. One or more acoustic wave modules may also be switchable in a filter. Other embodiments may be described and claimed.

Abstract: A reactance filter comprising suppression in the stop band comprises an input connection for applying an input signal, an output connection for outputting an output signal, at least series resonator, which is connected in a signal path between the input connection and the output connection, a parallel resonator, which is connected between the signal path and a connection in order to apply a reference potential, and an inductor, which is connected in series to the parallel resonator. A capacitor is connected by means of one connection between the at least one parallel resonator and the inductor and by means of the additional connection to the output connection. By connecting the reactance filter as a transmission filter in a duplexer component, the isolation in the receiving band of the duplexer component can be improved.

Abstract: A duplexer is proposed with a substrate which has at least one patterned metallization plane and on which, at least to some extent, a transmission path (TX) and a reception path (RX) are arranged, both of which are connected to an antenna connection (ANT). The duplexer comprises a transmission filter (TXF) which is arranged in the transmission path (TX) and which has a first acoustic wave filter (BAW1) with one or more resonators. Furthermore, the duplexer (DPL) comprises a reception filter (RXF) which is arranged in the reception path (RX) on the antenna side and which has a second acoustic wave filter (BAW2) with one or more resonators and also a single-ended output.

Abstract: A filter device for filtering signals via a pass-band includes series resonators connected in series between an input terminal and an output terminal, each of the series resonators having a corresponding parallel resonance frequency Fp and series resonance frequency Fs, and shunt resonators respectively connected between at least one of the series resonators and a ground voltage, each of the shunt resonators having a corresponding parallel resonance frequency Fp and series resonance frequency Fs. At least one series resonator has a corresponding series resonance frequency Fs outside the pass-band of the filter device, and at least one other series resonator has a corresponding series resonance frequency Fs inside the pass-band, and/or at least one shunt resonator has a corresponding parallel resonance frequency Fp outside the pass-band of the filter device, and at least one other shunt resonator has a corresponding parallel resonance frequency Fp inside the pass-band.

Abstract: An acoustic wave device includes: a piezoelectric substrate; a dielectric layer formed on the piezoelectric substrate; and first and second comb-tooth electrodes formed on the dielectric layer, the dielectric layer having a first thickness between the first comb-tooth electrodes and the piezoelectric substrate and a second thickness between the second comb-tooth electrodes and the piezoelectric substrate, the first and second thicknesses being different from each other.

Abstract: A circuit assembly includes a substrate having a substrate electrical circuit, opposite top and bottom substrate surfaces, and a substrate hole extending through the substrate. The circuit assembly also includes a discrete component assembly electrically connected to the substrate electrical circuit and a support member attached to the discrete component. At least a portion of the discrete component is physically mounted in the substrate hole.

Abstract: An electronic device includes a main circuit connected between an input terminal and an output terminal, and an auxiliary circuit connected in parallel to the main circuit between the input terminal and the output terminal. The main circuit includes a filter having a first passband and a stopband. The auxiliary circuit has a passing characteristic that allows a signal having a frequency in a certain frequency band inside the stopband to pass through the auxiliary circuit. The main circuit is configured to output a main signal in response to an input signal. The auxiliary circuit is configured to output an auxiliary signal in response to the input signal. The main signal and the auxiliary signal contain phase components opposite to each other in the certain frequency band inside the stopband. This electronic device has an attenuation amount in the stopband.

Abstract: A duplexer includes a transmission filter and a reception filter having different passbands, wherein: first resonators that are series resonators or parallel resonators included in the transmission and reception filters so as to form a skirt characteristic at a guard band side are a temperature compensated type piezoelectric thin film resonator or a surface acoustic wave resonator using Love waves, and second resonators that form a skirt characteristic at an opposite side to the guard band are one of a temperature non-compensated type piezoelectric thin film resonator, a surface acoustic wave resonator using a lithium tantalate substrate or a substrate made by bonding a lithium tantalate substrate on a sapphire substrate, and a surface acoustic wave resonator using Love waves.

Abstract: A signal separation device is a duplexer in which a reception frequency band is located at higher frequencies than a transmission frequency band. A series arm of a ladder transmission filter includes a plurality of series arm resonators, and parallel arms respectively include parallel arm resonators. The parallel arm resonators include the parallel arm resonators having resonant frequencies lower than those of the series arm resonators and the parallel arm resonator that has a resonant frequency which is located within the reception frequency band and which is higher than the resonant frequency of the series arm resonators and that has a lower capacitance than the series arm resonators and the parallel arm resonators.