A quartz-free miniaturized frequency reference for wireless systems.

摘要

While aggressive CMOS scaling has improved the performance of RF front end circuits by virtue of higher device switching frequency, the push towards miniaturization and integration of RF and base band circuits on the same substrate has come with its own perils, namely lower supply voltage, high leakage currents, substrate noise coupling, etc. The unavailability of high-Q passives, as a result of lossy silicon substrate, complicates RF design even further and has motivated RF designers to explore opportunities beyond conventional front end design. From an RF circuit designer's perspective, emerging high Q passive technologies hold the potential to dramatically reduce the power consumption and complexity of the RF active circuitry. One such MEMS component is the thin film bulk acoustic wave resonator (FBAR). FBAR based filters and switches in communications systems at very high frequencies are being continuously used for miniaturization of RF front end. Off-chip, bulky quartz crystal resonators used for frequency reference has huge area overhead for miniaturized wireless systems.;In recent years, around the world, great effort has been invested in the design of MEMS enabled low power RF front end circuits, especially oscillators for frequency synthesis. Oscillators using high quality factor FBAR resonators have been demonstrated to provide excellent phase noise, supply pushing, and power consumption performance. Other than being physically small, FBAR devices also offer an opportunity to be integrated with CMOS electronics, as they are batch-fabricated on semiconductor substrates.;This thesis explores the possibilities of designing miniaturized RF wireless systems without the use of a quartz crystal. A 1mm3 315--450MHz low power transmitter using an FBAR/CMOS reference is demonstrated to validate this concept. Various ways to address various frequency stability concerns for an FBAR/CMOS reference are explored. Also, design of an ultra-low power (600microW) quadrature voltage controlled RF oscillator using FBAR as a resonant tank is presented. To improve the tradeoff between oscillator power consumption, phase-noise, and reduce wasted die area, this work demonstrates the use of matched high Q FBAR resonators used as a tuning element in a 2GHz QVCO, and also introduces a new oscillator coupling mechanism for quadrature signal generation, which is applicable for both a FBAR- and an integrated LC-tuned QVCO.