Patent ID: 6853270
Filing Date: 2005-02-08
Classification: H03H

Abstract:
1. A surface acoustic wave filter comprising a piezoelectric substrate, and a first reflector, a first IDT, a second IDT, a third IDT, and a second reflector, arranged on the piezoelectric substrate in that order in the direction of propagation of a surface acoustic wave, wherein the first and third IDTs, connected in parallel to each other, are connected to an unbalanced signal terminal, and the second IDT includes two separate electrodes arranged in the direction of propagation of the surface acoustic wave, electrically connected in series with each other at a serial junction, and respectively connected to balanced signal terminals; wherein the outermost electrode fingers of the second IDT adjacent to the first IDT and the third IDT are connected to the serial junction; the outermost electrode finger of the first IDT adjacent to the second IDT is connected to the unbalanced signal terminal; the outermost electrode finger of the third IDT adjacent to the second IDT is grounded; and the first IDT only or both the first IDT and the third IDT are weighted so that the number of exciting regions of the surface acoustic wave in the first IDT adjacent to the second IDT is equal to the number of exciting regions in the third IDT adjacent to the second IDT.