Elastic wave filter with magnetically coupled LC parallel resonance circuits

摘要

A filter device includes a first LC parallel resonance circuit having a first inductance and connected between a line connecting an input terminal and an output terminal and a ground potential, a second LC parallel resonance circuit having a second inductance and connected between the line and the ground potential, and at least one elastic wave resonator that is connected between an end portion of the first LC parallel resonance circuit and an end portion of the second LC parallel resonance circuit. Attenuation-frequency characteristics of an LC filter including the first LC parallel resonance circuit, the second LC parallel resonance circuit, and a capacitive property and attenuation-frequency characteristics of the at least one elastic wave resonator are used.

主权项

1. A filter device comprising:
an input terminal; an output terminal; a line connecting the input terminal and the output terminal; a first LC parallel resonance circuit connected between the line and a ground potential and including a first inductance; a second LC parallel resonance circuit connected between the line and the ground potential and including a second inductance; and at least one elastic wave resonator connected between an end portion of the first LC parallel resonance circuit at a line side and an end portion of the second LC parallel resonance circuit at the line side; wherein the first and second LC parallel resonance circuits are electrically coupled by a capacitive property of the at least one elastic wave resonator; attenuation-frequency characteristics of an LC filter defined by the first and second LC parallel resonance circuits and the capacitive property of the at least one elastic wave resonator, and attenuation-frequency characteristics defined by an anti-resonance point of the at least one elastic wave resonator are combined; and the first inductance included in the first LC parallel resonance circuit and the second inductance included in the second LC parallel resonance circuit are magnetically coupled.