Integrated Micromechanical RF Circuits for Software-Defined Cognitive Radio

An evaluation of the potential for MEMS technologies to realize the RF front-end frequency gating spectrum analyzer function needed by true software-defined cognitive radios is presented. Here, the relevant MEMS technologies include vibrating micromechanical resonators that exhibit record on-chip Q‘s at GHz frequencies; medium-scale integrated micromechanical circuits that implement on/off switchable filter banks; and process technologies that integrate MEMS together with foundry CMOS transistors in a fully monolithic, low capacitance, single-chip process. Among the many issues that make realization of a frequency gating function a truly challenging proposition, e.g., resonator drift stability, mechanical circuit complexity, repeatability and fabrication tolerances, the need for resonators at GHz frequencies with simultaneous high Q (>30,000) and low impedance (e.g., 50 for conventional systems) is perhaps the most daunting. Some perspective on which resonator technologies, capacitive or piezoelectric, might best achieve these simultaneous attributes is also provided.