US Patent No. 10,659,007

TUNABLE FILTER, RADIO FREQUENCY FRONT-END CIRCUIT, AND COMMUNICATION APPARATUS


Patent No. 10,659,007
Issue Date May 19, 2020
Title Tunable Filter, Radio Frequency Front-end Circuit, And Communication Apparatus
Inventorship Takaya Wada, Kyoto (JP)
Koji Nosaka, Kyoto (JP)
Assignee MURATA MANUFACTURING CO., LTD., Kyoto (JP)

Claim of US Patent No. 10,659,007

1. A tunable filter having a tunable range of pass-band frequencies comprising:a series-arm resonant circuit; and
a parallel-arm resonant circuit,
wherein the series-arm resonant circuit and the parallel resonant arm circuit are connected in a ladder network,
wherein the series-arm resonant circuit and the parallel-arm resonant circuit each comprise at least one acoustic wave resonator and a variable capacitor,
wherein one of the series-arm resonant circuit and the parallel-arm resonant circuit comprises:
a first acoustic wave resonant circuit and a second acoustic wave resonant circuit, a resonant frequency of the first acoustic wave resonant circuit being different than a resonant frequency of the second acoustic wave resonant circuit, and
a switching circuit configured to selectively connect the first acoustic wave resonant circuit or the second acoustic wave resonant circuit to the variable capacitor, the filter having a first pass-band frequency when the variable capacitor is selectively connected to the first acoustic wave resonant circuit and a second pass-band frequency when the variable capacitor is selectively connected to the second acoustic wave resonant circuit,
wherein the first pass-band frequency is based on the resonant frequency of the first acoustic wave resonant circuit and a variable capacitance range of the variable capacitor, and the second pass-band frequency is based on the second acoustic wave resonant circuit and the variable capacitance range of the variable capacitor,
wherein a difference between the first pass-band frequency and the second pass-band frequency due to the different resonant frequencies of the first acoustic wave resonant circuit and the second acoustic wave resonant circuit is greater than a maximum difference between the first pass-band frequency and the second pass-band frequency due to the variable capacitance range of the variable capacitor, and
wherein the tunable filter further comprises:
a reactance element connected between a ground potential and the variable capacitor of the parallel-arm resonant circuit; and
a coupling variable capacitor connected between an input terminal of the tunable filter and a node between the variable capacitor and the reactance element,
wherein the parallel-arm circuit is connected to an output terminal of the tunable filter without the series-arm resonant circuit interposed between the parallel-arm resonant circuit and the output terminal.