Surface acoustic wave filter device.

摘要

A surface acoustic wave filter device which comprises a filter chip provided with an input transducer (2) and an output transducer (3) each composed of a pair of interdigital electrodes formed on a piezo-electric substrate (1) is accommodated in a casing (19) which has a plurality of externally-extending signal input and output terminals (18). A high-frequency voltage can be applied to the input transducer through the input terminals (18a, 18b) and electric outputs of the output transducer can be fed to a balanced differential amplifier through the output terminals (18c, 18d).

An electrostatic coupling means (30,31,32) is provided to forcibly couple at least one of a pair of the input terminals to at least one of a pair of the output terminals to equalize the levels of signals which are induced on the output terminals and which are not produced by acoustic surface waves.