PIEZOELECTRIC THIN-FILM FILTER

摘要

To provide a piezoelectric thin-film filter including resonators connected in a lattice pattern, which can achieve large attenuation at frequencies away from a passband and improve steepness near two ends of the passband without involving an additional special step. Second resonators C_2 or first and third resonators C_1 and Cx_1 connected in parallel form series-arm resonators or parallel-arm resonators C_1 connected in a lattice pattern. The capacitance of each second resonator C_2 is larger than the capacitance of each first resonator C_1. The capacitance of each third resonator Cx_1 is substantially equal to the difference between the capacitance of the second resonator C_2 and the capacitance of the first resonator C_1. The resonant frequency of the first resonator C_1 is higher than the resonant frequency of the second resonator C_2. The anti-resonant frequency of the third resonator Cx_1 is higher than the resonant frequency of the second resonator C_2 and lower than the resonant frequency of the first resonator C_1.