Fujitsu Corporation

Hideki Tominaga

Noboru Wakatsuki

Shigeo Tanji

A surface acoustic wave filter device in which a capacitative coupling means is provided to couple at least one of the terminals of the SAW input transducer to at least one of the terminals of the output transducer, in order to equalize the levels of signals which are induced on the pair of output terminals of said output transducer without assuming the form of surface acoustic waves. The stray inductive coupling which normally occurs between the input and output terminals of the SAW filter degrades filter performance. Since the inductive coupling to the two output terminals is normally unequal, the inductively coupled unfiltered signals cannot be completely rejected by a balanced differential amplifier. By equalizing the levels of unfiltered signals at the output terminal, effective rejection by a differential amplifier is possible.

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Suzaka, Japan

Hideki Tominaga