Patent ID: 7554422

Claim:
A filter module comprising: a substrate; a plurality of resonators formed on the substrate, having a piezoelectric layer supported on the substrate to spread over the principal surface of the substrate and utilizing longitudinal vibration along the thickness of the piezoelectric layer; a plurality of external connection terminals formed above or below the piezoelectric layer so as to be electrically connected to external circuits; a plurality of first interconnects formed to the side of the piezoelectric layer to which the external connection terminals are formed to electrically connect the external connection terminals to associated ones of the plurality of resonators; and a plurality of second interconnects through each of which predetermined resonators out of the plurality of resonators are electrically connected to each other, wherein: each of said plurality of resonators comprises a pair of electrodes consisting of lower and upper electrodes formed on the back and top surfaces of the piezoelectric layer, respectively, each said first interconnect is electrically connected to one of the associated upper and lower electrodes formed on the surface of the piezoelectric layer on which the associated external connection terminal is formed, each said second interconnect is used to electrically connect the associated pair of lower electrodes to each other or to electrically connect the associated pair of upper electrodes to each other, the external connection terminals include two input/output terminals through which signals are input/output to/from the filter module, at least one resonator unit is connected between the input/output terminals, said at least one resonator unit comprises a serial element including at least one of the plurality of resonators electrically connected in series between the input/output terminals and at least one parallel element including at least one of the plurality of resonators electrically connected between the input/output terminals and the ground, said plurality of resonators includes a first resonator, a second resonator, a third resonator, a fourth resonator, a fifth resonator and a sixth resonators, the serial element represents the first and second resonators electrically connected in series to each other, the at least one parallel element includes a parallel element connected between at least one of both ends of the serial element and the ground and a parallel element connected between a node at which the first and second resonators are connected to each other and the ground, the parallel element connected to the node represents the third resonator, the parallel element connected to at least one of the both ends of the serial element represents the fourth and fifth resonators, the fourth and fifth resonators being connected in series from the input/output terminal, and the parallel element connected to at least one of the both ends of the serial element includes the sixth resonators connected in parallel to the fifth resonator.