Lattice FBAR Filters: Basic Properties and Opportunities for Improving the Frequency Response

Abstract

The paper contains a relatively detailed consideration of lattice filters with bulk acoustic-wave resonators (FBAR): basic theory, investigation and improving of their design. First FBARs and their parameters are introduced briefly. Then the basic structure of lattice filters and its modification with twice lower number of resonators are introduced. A theory of lattice FBAR filters is presented, which allows unified explanation of many of their properties: condition for small or large gain of the filter; existence of maxima of the filter frequency response; emergence of transmission zeros; etc. The effect of using two different resonators instead of a single resonator in the arms of the lattice filter is investigated next. It is demonstrated that this approach suggests extension of the passband bandwidth and increasing the stopband attenuation. The properties of the considered filters are illustrated by comparing their frequency responses. Similar comparison between some good representatives of lattice and ladder filters is also given at the end, accompanied by comments about the benefits of both filter architectures. KeywordsFilm Bulk Acoustic-Wave Resonators (FBAR); RF Filters; FBAR Filters; Circuit Theory