Patent ID: 7898366
Filing Date: 2011-03-01
Classification: H03H

Abstract:
1. A balanced acoustic wave filter device comprising: an unbalanced terminal; first and second balanced terminals; a piezoelectric substrate; a first longitudinally coupled resonator type acoustic wave filter element arranged on the piezoelectric substrate, which is connected between the unbalanced terminal and the first balanced terminal, and which includes second, first, and third IDTs arranged in this order in an acoustic wave propagation direction and first and second reflectors arranged so as to sandwich a region including the first to third IDTs in the acoustic wave propagation direction; and a second longitudinally coupled resonator type acoustic wave filter element arranged on the piezoelectric substrate so as to be spaced away from the first acoustic wave filter element in the acoustic wave propagation direction, which is connected between the unbalanced terminal and the second balanced terminal, and which includes fifth, fourth, and sixth IDTs arranged in this order in the acoustic wave propagation direction and third and fourth reflectors arranged so as to sandwich a region including the fourth to sixth IDTs in the acoustic wave propagation direction; wherein one terminal of the first IDT and one terminal of the fourth IDT are connected to the unbalanced terminal, the other terminal of the first IDT and the other terminal of the fourth IDT are connected to a ground potential, one terminal of the second IDT and one terminal of the third IDT are connected to the first balanced terminal, the other terminal of the second IDT and the other terminal of the third IDT are connected to the ground potential, one terminal of the fifth IDT and one terminal of the sixth IDT are connected to the second balanced terminal, and the other terminal of the fifth IDT and the other terminal of the sixth IDT are connected to the ground potential; on the piezoelectric substrate, a first ground terminal connected to an external ground potential is arranged nearer to the unbalanced terminal relative to the first and second longitudinally coupled resonator type acoustic wave filter elements and nearer to the first longitudinally coupled resonator type acoustic wave filter element relative to the center between the first and second longitudinally coupled resonator type acoustic wave filter elements; and a first ground line that is arranged to connect the terminal, which is connected to the ground potential, of one of the second and third IDTs which is arranged nearer to the first ground terminal to the first ground terminal is longer than a second ground line that is arranged to connect the terminal, which is connected to the ground potential, of one of the fifth and sixth IDTs which is arranged nearer to the first ground terminal to the first ground terminal.