Internal electrical and mechanical phase inversion for coupled resonator-array MEMS filters

This paper reports on MEMS filters based on coupled resonator arrays designed using internal mechanical and electrical phase inversion principles. Four types of filter arrangements are described and their experimental validation using electrically and mechanically coupled silicon microfabricated resonators is presented. The internal phase inversion mechanisms are classified into four different categories based on the inversion principle and the nature of the coupling. The effects of capacitive parasitics on filter characteristics can be addressed by combining coupling mechanisms with phase inversion techniques without using external electrical phase inverter circuits. Filter metrics such as in-band ripple and minimum bandwidth are quantified and compared to previously reported results for silicon microresonators. The internal phase inversion mechanism enhances the design domain for MEMS resonator based filters. While, this paper discusses only a subset of resonator topologies, the principle can be extended to filters based on other resonator topologies as well. The techniques described here have applicability not only to the design of filters but also to the more effective interfacing to resonators in the presence of relatively large capacitive feedthrough parasitics.