Filter device and multiplexer

A band-pass filter device having a passband, comprising:

• an input terminal and an output terminal;
• at least one ground terminal;
• and
• a plurality of parallel arm resonators including a first parallel arm resonator and a second parallel arm resonator;
• wherein
• in a circuit configuration, a path connecting the input terminal and the output terminal is a series arm, and a plurality of paths branching from the series arm to the ground terminal are a plurality of parallel arms;
• the plurality of parallel arms include a first parallel arm and a second parallel arm branching to the ground terminal from portions of the series arm that are at a same or substantially a same potential, the first parallel arm resonator is provided in or on the first parallel arm, and the second parallel arm resonator is provided in or on the second parallel arm;
• the plurality of parallel arm resonators each include an IDT electrode including a plurality of electrode fingers, and, in each IDT electrode, when a direction in which the plurality of electrode fingers extend is an electrode finger extending direction, each IDT electrode includes an overlap region where adjacent electrode fingers overlap each other in a direction perpendicular or substantially perpendicular to the electrode finger extending direction;
• anti-resonant frequencies of the first parallel arm resonator and the second parallel arm resonator are both positioned within the passband;
• a resonant frequency of the first parallel arm resonator is higher than a resonant frequency of the second parallel arm resonator, a number of pairs of the electrode fingers of the IDT electrode in the first parallel arm resonator is greater than a number of pairs of the electrode fingers of the IDT electrode in the second parallel arm resonator, and, when a dimension of the overlap region along the electrode finger extending direction is an overlap width, the overlap width of the IDT electrode in the first parallel arm resonator is narrower than the overlap width of the IDT electrode in the second parallel arm resonator;
• and
• the resonant frequency of the first parallel arm resonator and the resonant frequency of the second parallel arm resonator are both positioned outside the passband on a low-frequency side of the passband.