Murata Manufacturing Co., Ltd.

Yutaka Tada

Hideharu Ieki

Takaharu Kawakatsu

A surface acoustic wave filter has pairs of interdigital transducers and reflectors formed on a 36&deg; Y-X LiTaO [object Object]

Saw filter with specified electrode dimensions

An elastic surface acoustic wave filter device provides balanced operation with a neutral terminal kept at a ground potential and is adaptable for any system of unbalanced input-to-balanced output or balanced input-to-unbalanced output even with an input and an output having a different characteristic impedance. A first elastic surface acoustic wave filter having a first predetermined phase is connected in a cascade arrangement to a second elastic surface acoustic wave filter having a phase that is different by about 180 degrees from the first predetermined phase to form a first set of cascaded elastic surface acoustic wave filters. A third elastic surface acoustic wave filter having the first predetermined phase is connected in a cascade arrangement to a fourth elastic surface acoustic wave filter having the predetermined phase to form a second set of cascaded elastic surface acoustic wave filters. One of input/output terminals of the first set of cascaded elastic surface acoustic wave filters and one of input/output terminals of the second set of cascaded elastic surface acoustic wave filters are electrically connected in parallel to an unbalanced input/output terminal. The other of input/output terminals of the first set of cascaded elastic surface acoustic wave filters and the other of input/output terminals of the second set of cascaded elastic surface acoustic wave filters are electrically connected in series to balanced input/output terminals.

Elastic surface acoustic wave filter device with balanced and unbalanced

A surface acoustic wave filter has an input electrode and an output electrode of a finger type with mutually parallel elongated fingers formed generally at a constant pitch on a piezoelectric substrate and sandwiched between a pair of reflectors. Two of these fingers of the input electrode which are the closest and the second closest to the output electrode, or two of these fingers of the output electrode which are the closest and the second closest to the input electrode, are connected together to a same grounding terminal. A plurality of such filters may be connected together to form a multi-stage filter.

Saw filter with successively grounded electrode fingers

A surface acoustic wave filter has pairs of interdigital transducers and reflectors formed on a 36.degree. Y-X LiTaO.sub.3 substrate, the reflectors sandwiching the interdigital transducers in between. The film thickness h of the electrode fingers of the interdigital transducers and the reflectors is such that 0.06.ltoreq.h/.lambda..ltoreq.0.01 where .lambda. is the wavelength of the surface acoustic wave adapted to be generated by the filter. The width-to-pitch ratio M/P of these electrode fingers for the interdigital transducers and the reflectors is such that M/P.gtoreq.0.6 in order to improve the shape factor of the filter.

An IIDT type surface acoustic wave filter (41) comprising a piezoelectric substrate and at least three IDTs (44 to 46) which are arranged on a surface of the piezoelectric substrate along the direction of surface wave propagation, the IDT (44) being inverted in phase with respect to the other IDT (46) while these IDTs (44) and (46) are connected in series to each other through the ground potential, thereby balancing inputs or outputs.

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Nagaokakyo, Japan

Yutaka Tada