Patent ID: 8125298

Claim:
An acoustic wave filter comprising: a first resonator that is placed in a serial arm and that has a resonance frequency f rs and an anti-resonance frequency f as ; and a second resonator that is placed in a parallel arm and that has a resonance frequency f rp and an anti-resonance frequency f ap , the first resonator and the second resonator are formed on a same substrate; the resonance frequency f rs of the first resonator is higher than the resonance frequency f rp of the second resonator; and the anti-resonance frequency f as of the first resonator is higher than the anti-resonance frequency f ap of the second resonator, the acoustic wave filter comprises a fourth resonator that is connected to the parallel arm in series with respect to the second resonator and that has a resonance frequency f rs and an anti-resonance frequency f as ; and the fourth resonator is formed on the substrate.