A duplexer includes a piezoelectric substrate, a receiving filter formed on the piezoelectric substrate, the receiving filter includes a plurality of resonators, and a transmitting filter formed on the piezoelectric substrate, the transmitting filter includes a plurality of resonators. One of the resonators of the receiving filter is a multi-mode type acoustic wave resonator having a capacitance that is two times or more the average capacitance of the other resonators formed on the piezoelectric substrate.

A switch module switches among a first state where first and second frequency bands are used in parallel, a second state where only the first frequency band is used, and a third state where none of the first and second frequency bands is used, and includes first, second, and third filters and an antenna switch. In the first state, a common terminal and the first and second filters are connected and the common terminal and the third filter are not connected. In the second state, the common terminal and the first and third filters are connected, and the common terminal and the second filter are not connected.

A filter module includes an inductor, a filter including first wiring, and second wiring between the inductor and the first wiring and being a direct-current floating potential. The inductor and the first wiring are magnetically coupled, the inductor and the second wiring are magnetically coupled, and the first wiring and the second wiring are capacitively coupled.

A filter circuit that secures the steepness from a pass range to an attenuation range while maintaining a wide-band transmission characteristic and a filter device including this filter circuit are formed. A filter circuit includes a first filter and a second filter. The first filter is a filter including an LC circuit in which a first frequency band is a pass band and a frequency band not higher than the first frequency band is an attenuation band. The second filter is a filter that attenuates a second frequency band within the first frequency band by using an attenuation pole produced by a resonance or an antiresonance of an acoustic wave resonator. Further, the first filter is placed closer to an antenna terminal than the second filter.

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.

A ladder filter in which the pass band is defined by serial arm resonators and first and second parallel arm resonators includes the serial arm resonators, the first and second parallel arm resonators, and a third parallel arm resonator. The third parallel arm resonator is connected in parallel to the first parallel arm resonator, the electrostatic capacitance of the third parallel arm resonator is smaller than that of the first parallel arm resonator, and the anti-resonant frequency of the third parallel arm resonator is positioned outside the pass band of the ladder filter. The anti-resonant frequency of the first parallel arm resonator is positioned at the high frequency side of the anti-resonant frequencies of the second parallel arm resonators.

An elastic wave device includes an LiNbO.sub.3 substrate, a first elastic wave resonator including a first IDT electrode and a first dielectric film, and a second elastic wave resonator including a second IDT electrode and a second dielectric film. A Rayleigh wave travels along at least one surface of the elastic wave device. A thickness of the first dielectric film differs from a thickness of the second dielectric film. A propagation direction of an elastic wave in the first elastic wave resonator coincides with a propagation direction of an elastic wave in the second elastic wave resonator. Euler angles of the LiNbO.sub.3 substrate fall within a range of (0°±5°, θ, 0°±10°).

An electronic component includes: a first substrate having a first surface; a second substrate having a second surface facing the first surface across an air gap; a first coil pattern that is located on the first surface so as to face the second surface across the air gap; a second coil pattern that is located in a second region on the second surface and faces the first surface across the air gap, at least a part of the second region overlapping with a first region in plan view, the first region being formed of a region in which the first coil pattern is located and a region surrounded by the first coil pattern; and a connection terminal connecting the first coil pattern and the second coil pattern.

A circuit comprising a receive block, a transmit block, and an antenna multiplexer. The antenna multiplexer includes an input port coupled to the transmit block, an output port coupled to the receive block, a common port for coupling to an antenna, and a receive filter coupled between the common port and the output port. The receive filter includes a first plurality of resonators coupled together in series between the common port and the output port including a compensation resonator coupled directly to the output port. A first angular range of a reflection coefficient of the antenna multiplexer over a transmission frequency band measured looking into the output port of the antenna multiplexer does not overlap with a second angular range of the conjugate of the reflection coefficient of the low noise amplifier over the transmission frequency band measured looking into an input of the low noise amplifier.

An acoustic wave device can have a plurality of coupling portions configured to electrically couple electrodes of the device to the substrate of the device to provide a bypass current pathway through the substrate for heat management. The substrate can be a semiconductor material, which can become more conductive as the temperature increases so that the bypass current pathway diverts more power through the substrate as the temperature increases. The acoustic wave device can be a surface acoustic wave device, which can have an interdigital transducer electrode that has the coupling portions on each of the bus bars and extending through the piezoelectric layer to contact the substrate. The acoustic wave device can be a bulk acoustic wave device in some implementations.