Acoustic wave filter, multiplexer, and communication apparatus

An acoustic wave filter comprising:

• a substrate comprising a piezoelectric substrate,
• a transmission terminal, an antenna terminal, and one or more reference potential terminals, which are located on the substrate,
• a transmission filter of a ladder-type filter for filtering signals from the transmission terminal and for outputting the result to the antenna terminal, the transmission filter comprising one or more serial resonators and one or more parallel resonators connected in a ladder configuration on the piezoelectric substrate, wherein the transmission terminal is connected to a first serial resonator of the one or more serial resonators that is closest to the transmission terminal,
• an additional resonator on the piezoelectric substrate, the additional resonator comprising an Interdigital transducer (IDT) electrode having a resonance frequency and antiresonance frequency located outside of a passband of the transmission filter, the IDT electrode connected to the transmission terminal at a stage before the transmission filter and connected to any of the one or more reference potential terminals, and
• a conductor layer which is short-circuited with the any of the one or more reference potential terminals connected with the additional resonator, the conductor layer comprising a broader area than a region where pluralities of electrode fingers are arranged of the IDT electrode in the additional resonator.

An acoustic wave filter comprising:

• a substrate comprising a piezoelectric substrate,
• a transmission terminal, an antenna terminal, and one or more reference potential terminals, which are located on the substrate,
• a transmission filter of a ladder-type filter for filtering signals from the transmission terminal and for outputting the result to the antenna terminal, the transmission filter comprising one or more serial resonators and one or more parallel resonators connected in a ladder configuration on the piezoelectric substrate, wherein the transmission terminal is connected to a first serial resonator of the one or more serial resonators that is closest to the transmission terminal,
• an additional resonator on the piezoelectric substrate, the additional resonator comprising an Interdigital transducer (IDT) electrode having a resonance frequency and antiresonance frequency located outside of a passband of the transmission filter, the IDT electrode connected to the transmission terminal at a stage before the transmission filter and connected to any of the one or more reference potential terminals, and
• an insulator which
• covers only the additional resonator among the one or more serial resonators, the one or more parallel resonators, and the additional resonator, or
• is thicker only on the additional resonator among the one or more serial resonators, the one or more parallel resonators, and the additional resonator.

An acoustic wave filter comprising:

• a substrate comprising a piezoelectric substrate,
• a transmission terminal, an antenna terminal, and one or more reference potential terminals, which are located on the substrate,
• a transmission filter of a ladder-type filter for filtering signals from the transmission terminal and for outputting the result to the antenna terminal, the transmission filter comprising one or more serial resonators and one or more parallel resonators connected in a ladder configuration on the piezoelectric substrate, wherein the transmission terminal is connected to a first serial resonator of the one or more serial resonators that is closest to the transmission terminal, and
• an additional resonator on the piezoelectric substrate, the additional resonator comprising an Interdigital transducer (IDT) electrode having a resonance frequency and antiresonance frequency located outside of a passband of the transmission filter, the IDT electrode connected to the transmission terminal at a stage before the transmission filter and connected to any of the one or more reference potential terminals,
• wherein
• the one or more serial resonators are a plurality of serial resonators,
• at least one serial resonator of the plurality of serial resonators is divided into a plurality of divided resonators which are connected in series with each other, and
• a number of divisions of the first serial resonator of the at least one serial resonator on a side closest to the transmission terminal is larger than a number of divisions of another serial resonator of the at least one serial resonator on a side closest to the antenna terminal.