| 摘要 |
<p>The intermediate frequency (IF) portion of a television receiver includes a surface acoustic wave (SAW) filter comprising first, second and third transducers mounted on a piezoelectric substrate. Each transducer includes at least two interdigitized comb-shaped conductors. The teeth of the comb-shaped conductors of the first transducer overlap in accordance with a predetermined envelope to define a desired IF response. The first and second transducers are connected to IF circuit portions of the receiver. The third transducer is positioned from the second transducer so that regenerated acoustic signals reflected from the first and third transducers to the second transducer are substantially 180 DEG out of phase at a predetermined frequency. The aperture W3, i.e., the overlap of the teeth of the comb-shaped elements, of the third transducer is selected with respect to the aperture W1 of the first transducer and the magnitude of the impedance of the combination of the first transducer and the electrical circuit connected to it so that regenerated acoustic signals reflected from the first and third transducers are substantially equal in magnitude at the predetermined frequency. The regenerated acoustic signals reflected from the first and third transducers are received by the second transducer to develop an electrical output signal substantially free of the influence of ghost-producing multiple reflection signals. The spacing between pairs of interdigitized teeth of the third transducer may be selected so that the center frequency associated with the third transducer is the frequency of the picture carrier, the frequency at which reflected signals are most readily manifested as ghost images.</p> |
