Over many years, RF-MEMS have been a hot topic in research at the technology
and device level. In particular, various kinds of mechanical Si-MEMS resonators
and piezoelectric BAW (bulk acoustic wave) resonators have been developed. The
BAW technology has made its way to commercial products for passive RF filters,
in particular for duplexers in RF transceiver front ends for cellular communications.
Beyond their use in filters, micromachined resonators can also be used in
conjunction with active devices in innovative circuits and architectures. Possible
applications are active tunable RF front-end filters, frequency synthesizers for
LO generation, or temperature-compensated MEMS resonators for frequency/time
reference potentially replacing the long-time used quartz crystal. Furthermore,
MEMS devices can advantageously be used in radios for further miniaturization
and reduction of power consumption.
This book presents a broad overview of this technology going from the MEMS
devices, mainly BAW and Si-MEMS resonators, to basic circuits such as oscillators
and finally complete systems such as ultralow-power MEMS-based radios. The
work is targeted at circuit and system designers. The fabrication process of the
MEMS devices is only covered at a minimal level. The discussion of MEMS
devices focuses on their properties and modeling, so they can be efficiently
used in circuits. Circuit design specific to MEMS devices is discussed in depth.
Traditional circuits cannot be used with high-Q resonators, and special techniques
for oscillator and filter design are required. Finally, several examples of system
architectures built around MEMS devices are described. It is particularly shown
how these architectures can exploit the potential of the MEMS devices to reduce
size and power consumption for applications such as wireless sensors where these
parameters are critical.