Patent ID: 9203377
Filing Date: 2015-12-01
Classification: H03H,H04B

Abstract:
1. A duplexer comprising: a first filter of which a first end is coupled to a common terminal, and a second end is coupled to a first terminal; and a second filter having a passband higher than a passband of the first filter, a first end of the second filter being coupled to the common terminal, and a second end of the second filter being coupled to a second terminal, wherein a phase shifter is located neither between the first filter and the common terminal nor between the second filter and the common terminal, the second filter is a ladder-type filter including piezoelectric thin film resonators connected in a ladder shape, a propagation constant in a direction perpendicular to a thickness direction of a piezoelectric thin film included in each of the piezoelectric thin film resonators is a real number at frequencies lower than a resonance frequency of corresponding one of the piezoelectric thin film resonators, a resonator at a first stage as viewed from a side of the common terminal is a parallel resonator in the second filter, and the duplexer comprises no inductor of which a first end is connected to a node between the common terminal and at least one of the first filter and the second filter, and a second end is connected to a ground.