TUNABLE FILTER

摘要

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.

主权项

1. 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 a first inductor 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.