Temperature Compensated CMOS and MEMS-CMOS Oscillators for Clock Generators and Frequency References
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Silicon alternatives to quartz crystal based oscillators to electronic system clocking are explored. A study of clocking requirements reveals widely different specifications for different applications. Traditional CMOS oscillator-based solutions are optimized for low-cost fully integrated micro-controller clock applications. The frequency variability of these clock generators is studied and techniques to compensate for this variability are proposed. The efficacy of these techniques in reducing variability is proven theoretically and experimentally. MEMS-resonator based oscillators, due to their exceptional quality factors, are identified as suitable integrated replacements to quartz based oscillators for higher accuracy applications such as data converter clocks. The frequency variation in these oscillators is identified and techniques to minimize the same are proposed and demonstrated. The sources of short-term variation (phase noise) in these oscillators are discussed and an inclusive theory of phase noise is developed. Techniques to improve phase noise are proposed. Findings from this research indicate that MEMS resonator based oscillators, may in future, outperform quartz based solutions in certain applications such as voltage controlled oscillators. The implications of these findings and potential directions for future research are identified.