Patent ID: 7868716
Filing Date: 2011-01-11
Classification: H03H

Abstract:
1. An acoustic wave filter apparatus comprising: a piezoelectric substrate; a first acoustic wave filter section disposed on the piezoelectric substrate, having a balance-unbalance conversion function and including an unbalance input/output terminal and first and second balance input/output terminals; a second acoustic wave filter section disposed on the piezoelectric substrate, having a different passband from that of the first acoustic wave filter, having a balance-unbalance conversion function, and including an unbalance input/output terminal and first and second balance input/output terminals; wherein the unbalance input/output terminals of the first and second acoustic wave filter sections are coupled to first and second unbalance terminals, respectively, the first balance input/output terminals of the first and second acoustic wave filter sections are commonly coupled to each other and then coupled to a first balance terminal, and the second balance input/output terminals of the first and second are commonly coupled to each other and then coupled to a second balance terminal; the first and second acoustic wave filter sections are configured so that a signal flowing to the first balance terminal and a signal flowing to the second balance terminal have opposite phases; the acoustic wave filter apparatus further comprising: a first acoustic wave resonator coupled between the first balance input/output terminal of the first acoustic wave filter section and the first balance terminal; a second acoustic wave resonator coupled between the first balance input/output terminal of the second acoustic wave filter section and the first balance terminal, the second acoustic wave resonator having a resonant frequency different from a resonant frequency of the first acoustic wave resonator; a third acoustic wave resonator coupled between the second balance input/output terminal of the first acoustic wave filter section and the second balance terminal; a fourth acoustic wave resonator coupled between the second balance input/output terminal of the second acoustic wave filter section and the second balance terminal, the fourth acoustic wave resonator having a resonant frequency different from a resonant frequency of the third acoustic wave resonator; and first, second, third and fourth wiring lines electrically coupling the first, second, third and fourth acoustic wave resonators to the first balance input/output terminal of the first acoustic wave filter section, the first balance input/output terminal of the second acoustic wave filter section, the second balance input/output terminal of the first acoustic wave filter section, and the second balance input/output terminal of the second acoustic wave filter section, respectively; wherein the second wiring line coupling the second acoustic wave resonator to the first balance input/output terminal of the second acoustic wave filter section and the third wiring line coupling the third acoustic wave resonator to the second balance input/output terminal of the first acoustic wave filter section cross each other on the piezoelectric substrate.