Patent ID: 7579932
Filing Date: 2009-08-25
Classification: H03H

Abstract:
1. A resonator type SAW filter comprising, on a piezoelectric substrate in a direction of propagation of a surface acoustic wave: an input interdigital transducer that excites the surface acoustic wave; an output interdigital transducer that receives the surface acoustic wave excited by the input interdigital transducer; a control interdigital transducer interposed between the input interdigital transducer and the output interdigital transducer that controls a state of the surface acoustic wave; and a pair of reflectors arranged on outer sides of both the input interdigital transducer and the output interdigital transducer, wherein the input interdigital transducer, the output interdigital transducer, and the control transducer are composed of electrode fingers each arranged inside two different zones C and E that are alternatively arranged; the electrode finger is formed with a width L set to approximately λ/4 on the condition of a wavelength of the surface acoustic wave set to λ; an electrode period length P is set as PC and a number of pairs MC of the electrode fingers is set to 1 in zone C and the electrode period length P is set as PE and a number of pairs ME of the electrode fingers is set to 1 in zone E on the condition that electrode period length P as a sum of the width L of the electrode finger and a spacing between the electrode fingers is equal to L+S; and a ratio PE/PC of the electrode period lengths in zones C and E falls within a range of 0.8<PE/PC<1; and the electrode fingers arranged in zones C and E are all connected to a feeder conductor.