| 摘要 |
PURPOSE:To eliminate the unrequired signal by direct waves, by locating the input and output terminals connected respectively to the transducers at the center and the both sides, symmetrically with respect to the center line. CONSTITUTION:On the surface acoustic wave filter chip 31 supported on the base, the transducers 32, 33, 34 consisting of the crossing finger electrodes are arranged transversally, and the terminals 36 to 41 are connected at their both poles. In this case, the terminals of the transducers 33, 34 at the both sides and the terminal of the transducer 44 at the center are located so that they are not asymmetrical to the center line of the transducer 44 at the center to eliminate the unnecessary signal by the direct waves. For example, when the terminals 36 and 39 are taken as the input terminal and the terminals 40 and 41 are taken as the output terminal by connecting the transducers 33 and 34 in series, the unnecessary signal by the direct waves is induced in phase at the terminals 40 and 41 due to the symmetry of constitution and it can be rejected by the transformer 43. |
