Patent ID: 6731188
Filing Date: 2004-05-04
Classification: H03H

Abstract:
A surface acoustic wave filter device comprising:a piezoelectric substrate; a first surface acoustic wave filter element having a plurality of IDTs arranged along a propagation direction of a surface acoustic wave on the piezoelectric substrate and having first and second terminals; and a second surface acoustic wave filter element having a plurality of IDTs including input/output IDTS arranged along the propagation direction of a surface acoustic wave on the piezoelectric substrate, the spacing between the input/output IDTs being greater than that of the first surface acoustic wave filter element by approximately half the wavelength of the surface acoustic wave, and having first and second terminals; the first terminals of the first and second surface acoustic wave filter elements being commonly connected to an unbalanced terminal, and the second terminals of the first and second surface acoustic wave filter elements being connected to a balanced terminal; wherein the total of the electrostatic capacitance values of the plurality of IDTs of the second surface acoustic wave filter element is greater than the total of the electrostatic capacitance values of the plurality of IDTs of the first surface acoustic wave filter element.