US 7,733,197 B2Granted

Duplexer and communications equipment

AssigneeKYOCERA Corporation

InventorMotoki Itou

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Abstract

A duplexer includes a piezoelectric substrate, a transmitting filter, and a receiving filter. A transmitting filter includes a ladder filter having a first resonator group which has one or more resonators in one or more series arms and one or more resonators in one or more parallel arms. A receiving filter has a passband higher than that of the transmitting filter, and includes a second resonator group which has one or more resonators in one or more series arms and one or more resonators in one or more parallel arms. A node connects both the transmitting filter and the receiving filter. The receive-side closest resonator closest to the node in the parallel arm is closer to the node than a resonator which is closest to the node in the series arm, and a resonance frequency of the receive-side closest resonator is lower than the passband of the transmitting filter.

Claims20

Dependent claims

A duplexer comprising:

a piezoelectric substrate;
a transmitting filter on the piezoelectric substrate, including a ladder filter having a first resonator group, the first resonator group comprising:
one or more resonators disposed in one or more series arms;
and
one or more resonators disposed in one or more parallel arms;
a receiving filter on the piezoelectric substrate, having a passband higher than that of the transmitting filter, and including a second resonator group, the second resonator group comprising:
one or more resonators disposed in one or more series arms;
and
one or more resonators disposed in one or more parallel arms;
a node connecting both a transmit-side end portion of the transmitting filter and a receive-side first portion of the receiving filter,
wherein the receive-side closest resonator which is in the second resonator group and is closest to the node in the parallel arm is closer to the node than a resonator which is in the second resonator group and is closest to the node in the series arm, and a resonance frequency of the receive-side closest resonator is lower than the passband of the transmitting filter.

8 more elements

Dependencies are inferred from the claim text.