Murata Manufacturing Co., Ltd.

Kimio Masaie

Haruo Morii

Yoshio Murata

Minoru Sakamoto

Kazuya Togawa

In a ladder-type piezoelectric filter having a series arm constituted by a plurality of series resonators connected in series and parallel arms respectively constituted by parallel resonators, each of the resonators being constructed using a piezoelectric plate, the direction of polarization of the piezoelectric plate of the series resonator arranged in at least one end of the series arm and the direction of polarization of the piezoelectric plate of the parallel resonator connected to the series resonator arranged in at least one end of the series arm are the same as seen from the side of a node of the series resonator arranged in the end and the parallel resonator connected to the series resonator.

Ladder-type piezoelectric filter

Two surface acoustic wave resonators are transversely formed with a minute spacing between them on a piezoelectric substrate. Said two surface acoustic wave resonators are oppositely formed to each other to become line-symmetry. Each of the surface acoustic wave resonator comprises an interdigital transducer and reflectors formed on its both sides. An input terminal and an output terminal are lead from the corresponding interdigital transducer. Between the input and the output terminals, an electrostatic capacity is bridged. The electrostatic capacity is formed on, for example, a piezoelectric substrate. In this case, the electrostatic capacity may be formed by alternately interdigitating each part of comb-like electrodes of the two interdigital transducers. Furthermore, the electrostatic capacity may be formed by alternately interdigitating both parts of the two reflector electrodes.

Surface acoustic wave filter

A piezoelectric filter for use in electrical and electronic equipment which includes a substrate of piezoelectric material, and electrode members provided on first and second surfaces of the substrate so as to form at least one set of resonator including a multi-mode resonator and a single resonator of the thickness-vibration, energy-trapping type. The multi-mode resonator serves as a series resonance element of a ladder type filter through utilization of the oblique or anti-symmetrical mode resonance of the multi-mode resonator, while the single resonator is used as a parallel resonance element of the ladder type filter.

Piezoelectric filter

A piezoelectric ceramic multiple mode filter exploiting the energy trapping theory, wherein the resistance between the ground electrode and the electrode for external connection is between several ohms and several tens of ohms. In a preferred embodiment, the connection lead between the ground electrode and the electrode for external connection is designed to provide the necessary resistance.

Piezoelectric ceramic filter

An improved quadrature detector for producing a frequency demodulated signal employing a low reactance phase shifter. A quadrature FM detector demodulates a frequency modulated signal by phase comparison of a signal directly from the limiter with a signal coupled through a multi-mode resonator tank circuit and a 90.degree. phase shift circuit. In the prior art the 90.degree. phase shift circuit includes a series coupled capacitor having a high reactance which tends to attenuate the signal and decrease the low distortion bandwidth. Accordingly in the present invention a coil is connected across the input or output terminals of the multi-mode tank circuit thereby enabling the phase shift circuit to employ a low reactance capacitor yielding an improved signal level and low distortion bandwidth.

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Nagaokakyo, Japan

Kimio Masaie