Vibrating RF MEMS for Low Power Communications
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C. T.-C. Nguyen, “Vibrating RF MEMS for low power communications (invited),” to be published in the Proceedings of the 2002 MRS Fall Meeting, Boston, Massachusetts, Dec. 2-6, 2002. Vibrating RF MEMS for Low Power Communications
Clark T.-C. Nguyen Center for Integrated Wireless Microsystems Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor, Michigan 48109-2122, U.S.A. ABSTRACT Micromechanical communication circuits fabricated via IC-compatible MEMS technologies and capable of low-loss filtering, mixing, switching, and frequency generation, are described with the intent to miniaturize wireless transceivers. Possible transceiver front-end architectures are then presented that use these micromechanical circuits in large quantities to substantially reduce power consumption. Technologies that integrate MEMS and transistor circuits into single-chip systems are then reviewed with an eye towards the possibility of single-chip communication transceivers. 1. INTRODUCTION Due to their need for high frequency selectivity and low noise frequency manipulation, portable wireless communication transceivers continue to rely on off-chip resonator technologies that interface with transistor electronics at the board-level. In particular, highly selective, low loss radio frequency (RF) and intermediate frequency (IF) bandpass filters generally require ceramic, SAW, or quartz acoustic resonator technologies with Q’s in excess of 1,000. In addition, LC resonator tanks with Q’s greater than 40 are required by voltage-controlled oscillators (VCO’s) to achieve sufficiently low phase noise. These off-chip resonator components then contribute to the substantial percentage (often up to 80%) of portable transceiver area taken up by board-level, passive components. Recent advances in IC-compatible microelectromechanical system (MEMS) technologies that make possible micro-scale, mechanical circuits capable of low-loss filtering, mixing, switching, and frequency generation, now suggest methods for boardless integration of wireless transceiver components. In fact, given the existence already of technologies that merge micromechanics with transistor circuits onto single silicon chips [1]-[8], single-chip transceivers may eventually be possible, perhaps using alternative architectures that maximize the use of passive, high-Q, micromechanical circuits to reduce power consumption for portable applications. This paper presents an overview of the micromechanical circuits and associated technologies expected to play key roles in reducing the size and power consumption of future communication transceivers. 2. MICROMECHANICAL CIRCUITS Although mechanical circuits, such as quartz crystal resonators and SAW filters, provide essential functions in the majority of transceiver designs, their numbers are generally suppressed due to their large size and finite cost. Unfortunately, when minimizing the use of high-Q components, designers often trade power for selectivity (i.e., Q), and hence, sacrifice transceiver per
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