Tunable filter
AssigneeMurata Manufacturing Co., Ltd.
InventorMichio Kadota
Life of this patent
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Abstract
A tunable filter is a ladder circuit tunable filter including serial arm resonators and a parallel arm resonator. The serial arm resonators and the parallel arm resonator include elastic wave resonators. Variable capacitors are connected in series to the serial arm resonators, a variable capacitor is connected in parallel to the parallel arm resonator, and first inductors are connected in series to the serial arm resonators. When an impedance at a resonant frequency of the serial arm resonators is Zrs and an impedance at a resonant frequency of the parallel arm resonator is Zrp, a ratio Zrs/Zrp is not greater than 1.
Claims19
A ladder circuit tunable filter comprising:
- a serial arm that connects an input end to an output end;
- a parallel arm that connects the serial arm to a ground potential;
- a plurality of serial arm resonators connected in series to each other in the serial arm;
- a parallel arm resonator provided in the parallel arm;
- a first variable capacitor connected in series to at least one of the plurality of serial arm resonators;
- a second variable capacitor connected in parallel to the parallel arm resonator;
- and
- first inductors respectively connected to each of the plurality of serial arm resonators;
- wherein
- when a resonant impedance of the plurality of serial arm resonators is represented by Zrs and a resonant impedance of the parallel arm resonator is represented by Zrp, a ratio Zrs/Zrp is not greater than 1.
Dependencies are inferred from the claim text.