Piezoelectric resonant filter and duplexer
First Claim
1. A piezoelectric resonant filter having frequency characteristic exhibiting a low frequency side attenuation extremum and a high frequency side attenuation extremum arranged on opposite sides of a pass band, said piezoelectric resonant filter comprising:
- a plurality of thin-film piezoelectric resonators, each including a piezoelectric thin film having piezoelectric characteristic, and a pair of excitation electrodes disposed on opposite surfaces of said piezoelectric thin film for applying an excitation voltage to said piezoelectric thin film,wherein a rate of frequency change in accordance with temperature change at a first frequency at which said low frequency side attenuation extremum appears is different from that at a second frequency at which said high frequency side attenuation extremum appears.
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Abstract
A piezoelectric resonant filter includes a group of series resonators and a group of parallel resonators for forming a ladder-type filter circuit. Each of the resonators has a piezoelectric thin film having piezoelectric characteristic, and lower and upper electrodes disposed on opposite surfaces of the piezoelectric thin film for applying an excitation voltage to the piezoelectric thin film. The group of the parallel resonators exhibits a low frequency side attenuation extremum in the filter whereas the group of the series resonators exhibits a high frequency side attenuation extremum in the filter. At least one of the group of the series resonators and the group of the parallel resonators has a temperature compensating layer for bringing the temperature coefficient of the resonant frequency close to zero.
140 Citations
20 Claims
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1. A piezoelectric resonant filter having frequency characteristic exhibiting a low frequency side attenuation extremum and a high frequency side attenuation extremum arranged on opposite sides of a pass band, said piezoelectric resonant filter comprising:
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a plurality of thin-film piezoelectric resonators, each including a piezoelectric thin film having piezoelectric characteristic, and a pair of excitation electrodes disposed on opposite surfaces of said piezoelectric thin film for applying an excitation voltage to said piezoelectric thin film, wherein a rate of frequency change in accordance with temperature change at a first frequency at which said low frequency side attenuation extremum appears is different from that at a second frequency at which said high frequency side attenuation extremum appears. - View Dependent Claims (2, 3, 4, 5)
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6. A duplexer connected to an antenna, comprising:
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a transmission filter for passing a transmission signal but cutting off a reception signal, said transmission filter having frequency characteristic exhibiting a first low frequency side attenuation extremum and a first high frequency side attenuation extremum arranged on opposite sides of a first pass band; and a reception filter for passing the reception signal but cutting off the transmission signal, said reception filter having frequency characteristic exhibiting a second low frequency side attenuation extremum and a second high frequency side attenuation extremum arranged on opposite sides of a second pass band different from said first pass band; said transmission filter as at least one of said transmission filter and said reception filter includes a plurality of thin-film piezoelectric resonators, each of said thin-film piezoelectric resonators having a piezoelectric thin film having piezoelectric characteristic, and a pair of excitation electrodes disposed on opposite surfaces of said piezoelectric thin film for applying an excitation voltage to said piezoelectric thin film; and the rate of frequency change in accordance with temperature change at a frequency which is one nearer to said second pass band out of a frequency exhibiting said first low frequency side attenuation extremum and a frequency exhibiting said first high frequency side attenuation extremum is lower than the rate of frequency change in accordance with temperature change at the other frequency exhibiting the other attenuation extremum. - View Dependent Claims (7, 8, 9, 10)
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11. A duplexer connected to an antenna, comprising:
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a transmission filter for passing a transmission signal but cutting off a reception signal, said transmission filter having frequency characteristic exhibiting a first low frequency side attenuation extremum and a first high frequency side attenuation extremum arranged on opposite sides of a first pass band; and a reception filter for passing the reception signal but cutting off the transmission signal, said reception filter having frequency characteristic exhibiting a second low frequency side attenuation extremum and a second high frequency side attenuation extremum arranged on opposite sides of a second pass band different from said first pass band; said reception filter as at least one of said transmission filter and said reception filter includes a plurality of thin-film piezoelectric resonators, each of said thin-film piezoelectric resonators having a piezoelectric thin film having piezoelectric characteristic, and a pair of excitation electrodes disposed on opposite surfaces of said piezoelectric thin film for applying an excitation voltage to said piezoelectric thin film; and the rate of frequency change in accordance with temperature change at a frequency which is one nearer to said first pass band out of a frequency exhibiting said second low frequency side attenuation extremum and a frequency exhibiting said second high frequency side attenuation extremum is lower than the rate of frequency change in accordance with temperature change at the other frequency exhibiting the other attenuation extremum. - View Dependent Claims (12, 13, 14, 15)
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16. A duplexer connected to an antenna, comprising:
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a transmission filter for passing a transmission signal but cutting off a reception signal, said transmission filter having frequency characteristic exhibiting a first low frequency side attenuation extremum and a first high frequency side attenuation extremum arranged on opposite sides of a first pass band; and a reception filter for passing the reception signal but cutting off the transmission signal, said reception filter having frequency characteristic exhibiting a second low frequency side attenuation extremum and a second high frequency side attenuation extremum arranged on opposite sides of a second pass band different from said first pass band; each of said transmission filter and said reception filter includes a plurality of thin-film piezoelectric resonators, each of said thin-film piezoelectric resonators having a piezoelectric thin film having piezoelectric characteristic, and a pair of excitation electrodes disposed on opposite surfaces of said piezoelectric thin film for applying an excitation voltage to said piezoelectric thin film; the rate of frequency change in accordance with temperature change at a frequency which is one nearer to said second pass band out of a frequency exhibiting said first low frequency side attenuation extremum and a frequency exhibiting said first high frequency side attenuation extremum is lower than the rate of frequency change in accordance with temperature change at the other frequency; and the rate of frequency change in accordance with temperature change at a frequency which is one nearer to said first pass band out of a frequency exhibiting said second low frequency side attenuation extremum and a frequency exhibiting said second high frequency side attenuation extremum is lower than the rate of frequency change in accordance with temperature change at the other frequency exhibiting the other attenuation extremum. - View Dependent Claims (17, 18, 19, 20)
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Specification