Patent ID: 7940147

Claim:
A balanced acoustic wave filter device comprising: an unbalance terminal; first and second balance terminals; a piezoelectric substrate; a first longitudinally-coupled acoustic wave filter element disposed on the piezoelectric substrate, including second, first, and third IDTs connected between the unbalance terminal and the first balance terminal and successively arranged in a direction of propagation of acoustic surface waves, and including first and second reflectors arranged on both sides, in a direction of propagation of acoustic surface waves, of an area in which the first to third IDTs are disposed; and a second longitudinally-coupled acoustic wave filter element disposed on the piezoelectric substrate in a spaced relationship, in the direction of propagation of acoustic surface waves, to a portion of the piezoelectric substrate in which the first acoustic wave filter element is disposed, including fifth, fourth and sixth IDTs connected between the unbalance terminal and the second balance terminal and successively arranged in the direction of propagation of acoustic surface waves, and including third and fourth reflectors arranged on both sides, in the direction of propagation of acoustic surface waves, of an area in which the fourth to sixth IDTs are disposed, the second acoustic wave filter element providing an output signal having a phase with respect to an input signal, which differs by 180° from a phase of an output signal of the first acoustic wave filter element with respect to an input signal; wherein the balanced acoustic wave filter device further comprises a first ground terminal which is disposed at a position closer to a side of the unbalance terminal than the first and second acoustic wave filter elements and shifted to the side of the first acoustic wave filter element from a middle point between the first and second acoustic wave filter elements, and which is electrically connected to a respective end of each of the second, third, fifth, and sixth IDTs, or to a respective end of each of the first and fourth IDTs; a third ground terminal which is electrically connected to the respective end of each of the second, third, fifth, and sixth IDTs, or to the respective end of each of the first and fourth IDTs, and which is arranged in a point-symmetric relationship relative to the first ground terminal with respect to the middle point between the first and second acoustic wave filter elements; a first signal wiring which is connected to a respective other end of each of the second and third IDTs, or to the other end of the first IDT, and which connects the first acoustic wave filter element and the first balance terminal to each other; a second signal wiring which is connected to a respective other end of each of the fifth and sixth IDTs, or to the other end of the fourth IDT, and which connects the second acoustic wave filter element and the second balance terminal to each other; and a second ground terminal disposed in an area between the first and second signal wirings.