Patent ID: 6940368
Filing Date: 2005-09-06
Classification: H03H

Abstract:
1. A surface acoustic wave filter, comprising: a symmetrical network of impedance elements with differential inputs/outputs, each impedance element being connected between two connection points of the network and having, between these connection points, an admittance (Y(f)) having a resonant frequency (f said two of said impedance elements are each connected between two electrical connection points forming two symmetrical branches of the network and supplied, when the filter is in operation, with substantially the same voltage and substantially the same current flowing through them, said impedance elements are grouped together to form a structure of the surface acoustic wave resonator type that comprises, in one and the same acoustic channel, two substantially identical transducers, two electrodes of which are connected to said connection points of said symmetrical branches of the network, respectively, and are positioned with respect to each other in such a way that the acoustic waves generated by the two said transducers are in phase; wherein when the network is of the ladder type, composed of series and parallel branches, the parallel branches of the network being composed of two portions of the same parallel branch that are symmetrical with respect to a zero-potential electrical connection point, two of said impedance elements, each connected between two electrical connection points forming, respectively, two parallel branch portions, with a common connection point formed from said zero-potential connection point, are grouped together to form said structure of the surface acoustic wave resonator type, wherein said network of said impedance elements is of the ladder type, comprising one or more symmetrical segments in series, each formed from two series branches and two parallel branches and in that the impedance elements of each section are grouped together to form three said structures of the surface acoustic wave resonator type, a first structure comprising two transducers, the electrodes of which are connected to the connection points of two series branches of the structure, a second structure comprising two transducers, the electrodes of which are each connected, on the one hand, to an electrical connection point of each transducer of the first structure and, on the other hand, to a zero-potential common electrical connection point and a third structure comprising two transducers, the electrodes of which are each connected on the one hand, to the second electrical connection point of each transducer of the first structure and, on the other hand, to a zero-potential common electrical connection point.