Oki Electric Industry Co., Ltd.

Hisanori Ehara

Tomokazu Komazaki

Yoshiaki Fujita

Kazushige Noguchi

Hajime Shimamura

Kenichi Anasako

Yoshio Okada

Wataru Ohashi

Satoshi Terada

Yoshikazu Kihara

A surface acoustic wave filter includes an antenna terminal, a transmitting filter and a variable branching line both of which are coupled to the antenna terminal and a receiving filter coupled to the variable branching line. The transmitting filter has a first end series-arm SAW resonator, a second end series-arm SAW resonator, a middle series-arm SAW resonator coupled between the first and second end series-arm SAW resonators and parallel-arm SAW resonators. Each of the first and second end series-arm SAW resonator has a first resonance frequency. The middle series-arm SAW resonator has a second resonance frequency that is higher than the first resonance frequency.

Transmitting filter including SAW resonators

Acoustic wave branching filter having transmitting filter with optimal power handling

A surface acoustic wave filter includes an antenna terminal, an antenna, a transmitting filter, a branching line and a receiving filter. The antenna is coupled to the antenna terminal. The transmitting filter is coupled to the antenna terminal. The transmitting filter receives an electrical power. The branching line is coupled to the antenna terminal. The branching line has a first length that is longer than &#x3bb;/4 length so that the electrical power received by the transmitting filter when the antenna terminal is opened is smaller than when the antenna terminal is terminated, wherein &#x3bb; is a wave length of a center frequency of transmitted and received bands of the surface acoustic wave filter. The receiving filter is coupled to the branching line.

Surface acoustic wave filter

A surface acoustic wave duplexer includes a piezoelectric substrate; a transmitting filter formed on the piezoelectric substrate; a receiving filter formed on the piezoelectric substrate; a transmitting (Tx) branching line formed on the piezoelectric substrate; and a receiving (Rx) branching line formed on the piezoelectric substrate.

Surface acoustic wave duplexer and portable communication device using the same

In a differential surface acoustic wave resonator, when an unbalanced electric signal is inputted between an input terminal and an output terminal connected to a ground potential, this electric signal is inputted to two-terminal-pair surface acoustic wave resonators and . The electric signal inputted to the two-terminal-pair surface acoustic wave resonator is converted into a surface acoustic wave, and thereafter it is again converted into an electric signal to be outputted to a two-terminal-pair surface acoustic wave resonator . The electric signal inputted to the two-terminal-pair surface acoustic wave resonator is converted into a surface acoustic wave, and thereafter it is again converted into an electric signal to be outputted from an output terminal of the differential surface acoustic wave filter as a balanced signal. On the other hand, the electric signal inputted to the two-terminal-pair surface acoustic wave resonator is converted into a surface acoustic wave, and thereafter it is again converted into an electric signal to be outputted to a two-terminal-pair surface acoustic wave resonator . The electric signal inputted to the two-terminal-pair surface acoustic wave resonator is converted into a surface acoustic wave, and thereafter it is again converted into an electric signal to be outputted from an output terminal of the differential surface acoustic wave filter as a balanced signal. Here, in the respective two-terminal-pair surface acoustic wave resonators to , the phase of the electric signal to be inputted is substantially &deg; different from that of the electric signal to be outputted. The balanced signals having the same phase and the same amplitude are outputted from the two output terminals of the differential surface acoustic wave filter.

Differential surface acoustic wave filter

A surface-acoustic-wave filter has a pair of series-arm surface-acoustic-wave resonators and a shunt-arm surface-acoustic-wave resonator coupled in a T configuration. An additional bridging surface-acoustic-wave resonator is coupled between the input and output terminals, in parallel with the series arm. The bridging surface-acoustic-wave resonator provides enhanced attenuation of spurious signals at multiples of the passband frequency.

Saw resonator filter with bridged-T configuration

A surface-acoustic-wave filter couples a two-port surface-acoustic-wave resonator filter circuit coupled in parallel or in series with a two-port impedance circuit. The two-port impedance circuit has an impedance that creates a pole of attenuation, by making the open-circuit impedance of the surface-acoustic-wave filter equal to the short-circuit impedance. High attenuation over a wide range of stopband frequencies is obtained in this way, combined with steep roll-off between the passband and stopband.

Growing community of inventors

Tokyo, Japan

Hisanori Ehara