Patent ID: 7880561

Claim:
A surface acoustic wave filter device comprising: a piezoelectric substrate; first and second longitudinally coupled resonator type surface acoustic wave 5-IDT filter units that are cascade-connected to one another and arranged on the piezoelectric substrate; and at least two surface acoustic wave resonators arranged on the piezoelectric substrate; wherein each of the first and second surface acoustic wave filter units includes a first IDT, second and third IDTs arranged on both sides of the first IDT in a surface acoustic wave propagation direction, fourth and fifth IDTs arranged in the surface acoustic wave propagation direction on both sides of an area in which the first through third IDTs are arranged, and first and second reflectors arranged in the surface acoustic wave propagation direction; each of the first IDTs of the first and second surface acoustic wave filter units includes first and second sub-IDTs that are defined by dividing the first respective IDTs in the surface acoustic wave propagation direction; the surface acoustic wave propagation directions of the first and second the surface acoustic wave filter units being parallel or substantially parallel with each other; a first signal line electrically connects the fourth IDTs of the first and second surface acoustic wave filter units; a second signal line electrically connects the first sub-IDT of the first IDTs of the first and second surface acoustic wave filter units; a third signal line electrically connects the second sub-IDT of the first IDTs of the first and second surface acoustic wave filter units; a fourth signal line electrically connects the fifth IDTs of the first and second surface acoustic wave filter units; a phase of an electrical signal flowing through the first signal line is different by about 180° from a phase of an electrical signal flowing through the second signal line, and a phase of an electrical signal flowing through the third signal line is different by about 180° from a phase of an electrical signal flowing through the fourth signal line; and at least one of the at least two surface acoustic wave resonators is electrically connected between the first signal line and the second signal line, and at least one other of the at least two surface acoustic wave resonators is electrically connected between the third signal line and the fourth signal line.