Band rejection filter
AssigneeMurata Manufacturing Co., Ltd.
InventorsNorihiko Nakahashi, Yasumasa Taniguchi
Life of this patent
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Abstract
An inexpensive compact band rejection filter realizes a high sharpness of a filter characteristic at ends of passbands and has a large attenuation. In the band rejection filter, at least one of a plurality of elastic wave resonators, which contributes to formation of a transition band, has a propagation angle larger than those of the other elastic wave resonators. Accordingly, the at least one of the plurality of elastic wave resonators which contributes to the formation of the transition band has an electromechanical coupling coefficient that is smaller than electromechanical coupling coefficients of the other elastic wave resonators.
Claims22
A band rejection filter comprising:
- a ladder circuit including:
- a series arm arranged to connect an input terminal and an output terminal to each other;
- a parallel arm which is connected between the series arm and a ground potential;
- a plurality of elastic wave resonators which are disposed in at least one of the series arm and the parallel arm;
- an inductance element which is disposed in at least one of the series arm and the parallel arm;
- and
- a first attenuation band, a first passband which is provided by an inductance of the inductance element and adjacent to the first attenuation band, a second attenuation band which is provided by resonances of the plurality of elastic wave resonators and included in the first passband, and a transition band which is adjacent to the second attenuation band;
- wherein
- at least one of the elastic wave resonators which contributes to formation of the transition band has a propagation angle larger than propagation angles of the others of the elastic wave resonators;
- and
- the at least one of the elastic wave resonators having the propagation angle larger than the propagation angles of the others of the elastic wave resonators includes one of an elastic wave resonator of the plurality of elastic wave resonators which has a lowest resonant frequency and an elastic wave resonator of the plurality of elastic wave resonators which has a highest anti-resonant frequency.
A band rejection filter comprising:
- a ladder circuit including:
- a series arm arranged to connect an input terminal and an output terminal to each other;
- a parallel arm which is connected between the series arm and a ground potential;
- a plurality of elastic wave resonators which are disposed in at least one of the series arm and the parallel arm;
- an inductance element which is disposed in at least one of the series arm and the parallel arm;
- and
- a first attenuation band, a first passband which is provided by an inductance of the inductance element and adjacent to the first attenuation band, a second attenuation band which is provided by resonances of the plurality of elastic wave resonators included in the first passband, and a transition band which is adjacent to the second attenuation band;
- wherein
- at least one of the elastic wave resonators which contributes to formation of the transition band has a propagation angle larger than propagation angle of the others of the elastic wave resonators, and therefore, the at least one of the elastic wave resonators which contributes to the formation of the transition band has an electromechanical coupling coefficient smaller than electromechanical coupling coefficients of the others of the elastic wave resonators;
- and
- the at least one of the elastic wave resonators having the propagation angle larger than the propagation angles of the others of the elastic wave resonators includes one of an elastic wave resonator of the plurality of elastic wave resonators which has a lowest resonant frequency and an elastic wave resonator of the plurality of elastic wave resonators which has a highest anti-resonant frequency.
The band rejection filter according to claim l5, wherein at least one of the elastic wave resonators has an anti-resonant frequency different from anti-resonant frequencies of the others of the elastic wave resonators, and the one of the elastic wave resonators which has the highest anti-resonant frequency has the propagation angle larger than the propagation angle of the others of the elastic wave resonators.
Dependencies are inferred from the claim text.