| 摘要 |
<p>The IF portion of a television receiver includes a surface acoustic wave filter comprising at least two conductors having electrodes extending therefrom to form comb-shaped elements mounted on one surface of a piezoelectric substrate. Respective electrodes of the comb-shaped elements are interleaved in alternated relationship to form a transducer for launching an acoustic signal along the surface of the substrate in response to an electrical signal coupled between the two conductors. The overlap of each pair of alternated electrodes is substantially uniform throughout the transducer. The transducer includes two end portions and a center portion between the end portions. However, because the location of the center of each pair of alternated electrodes from the location of the center of an adjacent pair of alternated electrodes is substantially the same throughout the transducer, the transducer is continuous. The end portions are arranged with respect to the center portion to generate acoustic signals which have amplitudes less than, and desirably at least approximately equal to one-half, the amplitude of the acoustic signal generated by the center portion so as to minimize the amplitudes of undesirable sidelobes which tend to reduce the frequency selectivity of the SAW filter. In preferred embodiments, the amplitudes of components generated by the end portions are electrically adjustable to control the frequency selectivity of the SAW filter.</p> |
