Surface acoustic wave filter device, duplexer including the same, and electronic apparatus including the same

摘要

A surface acoustic wave (SAW) filter device includes an input port for receiving an unbalanced signal, a pair of input/output ports, a first SAW filter for receiving the unbalanced signal from the input port and outputting balanced signals to the pair of input/output ports, a second SAW filter for receiving the balanced signals output from the pair of input/output ports and outputting balanced signals, and a pair of output ports for outputting the balanced signals output from the second SAW filter. The first SAW filter includes a first longitudinally-coupled SAW resonator having a first unbalanced signal input port and first and second balanced signal output ports, and a second longitudinally-coupled SAW resonator having a second unbalanced signal input port and third and fourth balanced signal output port. The first and second unbalanced signal input ports are electrically connected to the input port. The first and third balanced signal output ports both are electrically connected to one of the pair of input/output ports. The second and fourth balanced signal output ports both are electrically connected to another of the pair of input/output ports. This SAW filter device can suppress spurious and has a small insertion loss.