| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave filter which can take an unbalanced balanced input output circuit structure with a characteristic of a low impedance input and output by reducing the number of parts, and further can obtain a desirable characteristic for out-of-band attenuation. <P>SOLUTION: A structure that two groups of longitudinal coupling mode resonator type SAW filter units (3IDT-LCMR) having input and output phases different from each other at 180 degrees is proposed. Central IDT electrodes 11A, 12A of both the SAW filter units are grounded at one terminal, and connected at other terminals in parallel to be an unbalanced input port. Two terminals whose phases are the same among four outer IDT electrodes 11B, 11C and 12B, 12C of both the SAW filter units are connected in parallel to be a balanced output port. The outer IDT electrodes 11B, 11C and 12B, 12C may be connected in parallel to be an unbalanced input port, and the central IDT electrodes 11A, 11B may be connected in parallel to be a balanced output port. In addition, the output port may be unbalanced, and the input port may be balanced. <P>COPYRIGHT: (C)2007,JPO&INPIT</p> |
