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Tunable filter, radio frequency front-end circuit, and communication apparatus

  • US 10,659,007 B2
  • Filed: 04/18/2018
  • Issued: 05/19/2020
  • Est. Priority Date: 10/19/2015
  • Status: Active Grant
First Claim
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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, anda 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, andwherein 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.

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