Patent ID: 6509814
Filing Date: 2003-01-21
Classification: H03H

Abstract:
A ladder filter comprising a plurality of bulk acoustic wave resonators, the resonators comprising a plurality of series resonators in series between an input port and an output port of the filter, and one or more shunt resonators each connected between a junction between two series resonators and a common terminal, the series resonators comprising an input series resonator connected to the input port and an output series resonator connected to the output port, and wherein the series and shunt resonators are designed to satisfy:Cseries=(2&ohgr;shunt)/(&ohgr;series2Rom) Cshunt=(2&ohgr;shuntm)/(&ohgr;series2Ro) where Cseries is the static capacitance of the input and output series resonators; Cshunt is the static capacitance of the or each shunt resonator, &ohgr;series and &ohgr;shunt are the angular resonant frequencies respectively of the series and shunt resonators, Ro is a desired input and output impedance of the filter, and m is a parameter which is equal to the square root of the ratio of shunt-to-series static capacitance.