FILTER CIRCUIT USING SURFACE ACOUSTIC WAVE FILTER, AND DUPLEXER

摘要

PROBLEM TO BE SOLVED: To provide a filter circuit and duplexer which are stable against temperature variation and to provide a duplexer which prevent a high-output signal from a transmitter from being inputted to a surface acoustic wave filter.

SOLUTION: The filter circuit 1 including a band passing type surface acoustic wave filter 2 and a trap means 3 which is connected to the input side or output side of the filter 2 and equipped with a dielectric resonator 4 is so constituted that the resonance frequency of the dielectric resonator 4 is positioned in the suppression band of the surface acoustic wave filter 2 and temperature variation in the attenuation quantity of the trap means 3 cancels temperature variation in the attenuation quality of the surface acoustic filter 2 in the transition band of the surface acoustic wave filter 2 on the resonance frequency side. The filter circuit 1 in which an attenuation pole is formed in a transmission band is used for the duplexer 6.

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