Patent ID: 6717487
Filing Date: 2004-04-06
Classification: H03H

Abstract:
A surface acoustic wave filter comprising:a piezoelectric substrate; and a plurality of one-terminal-pair surface acoustic resonators disposed on said piezoelectric substrate, each of the plurality of one-terminal-pair surface acoustic resonators including interdigital electrodes disposed on said piezoelectric substrate, and an insulating film deposited on and adhered to the interdigital electrodes; wherein at least one of said plurality of one-terminal-pair surface acoustic resonators is a series arm resonator, and at least one of the remaining one-terminal-pair surface acoustic resonators is a parallel arm resonator, the series arm resonator and the parallel arm resonator are coupled in a ladder arrangement, the electrode duty of the parallel arm resonator is greater than the electrode duty of the series arm resonator, the electrode duty of a one-terminal pair surface acoustic resonator being defined by the following equation (1): electrode duty=2Ã—W/&lgr;â€ƒâ€ƒ(1) where &lgr; denotes the wavelength of the one-terminal-pair surface acoustic wave resonator, and W denotes the line width of an interdigital electrode.