Patent ID: 6472959
Filing Date: 2002-10-29
Classification: H03H

Abstract:
A filter having an input and an output, the filter comprising:a longitudinally coupled double mode resonator (LCR) comprising a plurality of interdigital transducers (IDTs), coupled between the input and the output, longitudinally coupled with one another on a surface of a piezoelectric substrate with an orientation for transducing and propagating shallow bulk acoustic waves (SBAWs), the LCR having a pass band and upper and lower stop bands and having a relatively poor attenuation in a raised shoulder region in the upper stop band on a high frequency side of the pass band; and a reactance coupled between the input and the output, the reactance being selected to couple a signal from the input to the output with a phase change generally opposite to a phase change of a signal coupled from the input to the output via the LCR at frequencies of said raised shoulder region, and with an attenuation such that the filter comprising the LCR and the reactance has a greater attenuation than the LCR at frequencies of said raised shoulder region.