Patent ID: 6844795

Claim:
A constant K SAW (Surface Acoustic Wave) filter comprising: a plurality of serial arm resonators and a plurality of parallel arm resonators interconnected in pairs in a multiple-stage, ladder configuration; and a resonating device serially connected to one of said serial arm resonators and having an attenuation pole frequency higher than an attenuation pole frequency of said one of said serial arm resonators, said resonating device functioning, at the attenuation pole frequency of said one of said serial arm resonators, as a capacitance without performing substantial attenuation, wherein said resonating device has an antiresonance frequency ranging from 1.8 times to 2.2 times inclusive, or ranging from 2.7 times to 3.3 times inclusive, as high as an antiresonance frequency of said one of said serial arm resonators, and wherein said resonating device has a damping capacitance higher than a damping capacitance of said one of said serial arm resonators.