Patent ID: 7369016
Filing Date: 2008-05-06
Classification: H03H

Abstract:
1. A balanced SAW filter having an unbalanced terminal and first and second balanced terminals, comprising: a piezoelectric substrate; a first longitudinally-coupled-resonator SAW filter element provided on the piezoelectric substrate, the first longitudinally-coupled-resonator SAW filter element including first to fifth IDTs arranged in a propagation direction of surface acoustic waves, each of the first to fifth IDTs including a pair of bus bars; a second longitudinally-coupled-resonator SAW filter element including, on the piezoelectric substrate, sixth to tenth IDTs arranged in the propagation direction of surface acoustic waves, the eighth IDT at a center including a pair of bus bars, one of the bus bars being divided to provide first and second sub-IDT portions, the first sub-IDT portion of the eighth IDT and the sixth IDT being connected to the first balanced terminal, the second sub-IDT portion of the eighth IDT and the tenth IDT being connected to the second balanced terminal, and first ends of the first, third, and fifth IDTs being connected to the unbalanced terminal; a first wiring line connecting the second IDT to the seventh IDT; and a second wiring line connecting the fourth IDT to the ninth IDT; wherein the first to tenth IDTs are arranged such that the phase of an electrical signal transmitted through the first wiring line differs by 180 degrees from the phase of an electrical signal transmitted through the second wiring line.