Oki Electric Industry Co., Ltd.

Nippon Hoso' Kyokai

Nobuyoshi Sakamoto

Kiyoshi Nagai

Ou Hok Huor

Takao Chiba

Kenji Kohro

A surface-acoustic-wave device includes a surface-acoustic-wave filter with a capacitance connected in parallel between its input and output leads. The capacitance improves the attenuation characteristic of the device on the high-frequency side of the center frequency.

Surface-acoustic-wave device with a capacitance coupled between input

A surface-acoustic-wave filter is of a multi-transducer arrangement including a plurality of input interdigital transducers and a plurality of output interdigital transducers. These input and output transducers are alternately and parallelly disposed on a piezo-electric substrate so as to be spaced intercentral distances l.sub.1 through l.sub.n apart. When one of the intercentral distances is a reference distance l.sub.1, the respective intercentral distances l.sub.1 through l.sub.n satisfies the following relationships:

Surface-acoustic-wave filter

An acoustic surface wave transducer with a transmission interdigital electrode (2A) and a reception interdigital electrode (2B in FIG. 10A-D) on a piezoelectric surface (1) has been improved by reducing inband dispersion of frequency characteristics by providing an edge effect canceler (k.sub.1), which cancels an undesired surface wave (E-a, E-b) generated at the external edge of the extreme end finger of the interdigital electrodes. Said edge effect canceler is constructed so that the length of the extreme end finger (11a) of the interdigital electrode (10, 20 in FIG.5A) is half of the length of the second extreme end finger (12a) of said interdigital electrode, and the spacing between said extreme end finger and the second extreme end finger is 1/2 wavelength of the acoustic surface Wave. Thus, the phase of the undesired surface wave generated by the extreme end finger of the transmission interdigital electrode is opposite to that generated by the second extreme end finger at the reception side, and the strength of the former is the same as that of the latter. Thus, those surface waves are cancelled by each other at the reception side, and the inband deviation or dispersion in amplitude characteristics and/or group delay characteristics of the transducer is improved.

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Tokyo, Japan

Nobuyoshi Sakamoto