Patent ID: 6031435
Filing Date: 2000-02-29
Classification: H03H

Abstract:
A multiple-stage ladder type SAW filter having a ladder network configuration constructed by cascade-connecting a plurality of ladder stages such that each of said ladder stages is made of a series-arm SAW resonator and a shunt-arm SAW resonator formed on a piezoelectric substrate, whereineach of said series-arm SAW resonators and each of said shunt-arm SAW resonators comprise an inter-digital transducer having a first electrode finger group that extends from one side and a second electrode finger group that extends from an opposite side such that electrode fingers of said first electrode finger group and electrode fingers of said second electrode finger group are arranged alternately and such that a distance between a center line that bisects a width of any given electrode finger of said first electrode finger group and a center line that bisects a width of any electrode finger of said first electrode finger group adjacent to said given electrode finger of said first electrode finger group is set to a prescribed electrode pitch, and such that a distance between a center line that bisects a width of any given electrode finger of said second electrode finger group and a center line that bisects a width of any electrode finger of said second electrode finger group adjacent to said given electrode finger of said second electrode finger group is also set to said prescribed electrode pitch and whereinsaid electrode pitches of said series-arm SAW resonators are gradually decreased from a first ladder-stage to a last ladder-stage.