| 摘要 |
A longitudinally-coupled-resonator-type surface-acoustic-wave filter (101) in which three interdigital transducers (102-4) are formed on a piezoelectric substrate (501) in the direction in which surface acoustic waves propagate is provided. An interdigital transducer (103) disposed at the center among the three interdigital transducers of the longitudinally-coupled-resonator-type surface-acoustic-wave filter is divided into two parts (110,111) substantially symmetrically in the propagation direction of the surface acoustic waves and the two parts (110,111) are connected to balanced signal terminals (108,109), respectively. Left and right interdigital transducers (102,104) of which the polarities are inverted to each other are connected to an unbalanced signal terminal (107) to provide a balanced-to-unbalanced conversion function. A reactance component (120) formed, on the piezoelectric substrate (501), inside a package, or outside the package is connected to either of the balanced signal terminals (108). |
