Piezoelectric resonant filter and duplexer

A duplexer connected to an antenna, comprising:

• 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.

A duplexer connected to an antenna, comprising:

• 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.

A duplexer connected to an antenna, comprising:

• 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.