Stability of Ultra-Low Power Wine-Glass Disk Based Reference Oscillators
In portable wireless applications, two features of the local oscillator are critical: high stability and low power. Frequency instability of oscillators takes many forms, from short-term jitter (phase noise) to long term drift as well as often overlooked factors such as sensitivity to acceleration forces. External vibration can couple into the reference oscillator through various mechanisms and introduce phase noise, ultimately limiting oscillator performance. Furthermore, as the field of mobile communications develops, the need for compact and low power oscillators only becomes more demanding. A MEMS-based oscillator, constructed from a custom CMOS amplifier referenced to a 61-MHz vibrating wine-glass disk resonator, provides a unique solution to these requirements. Despite concerns that the tiny size of MEMS resonators may make these instabilities too large for real-world applications, their performance is found to be quite good, comparable or even superior to many low-cost quartz oscillators in each respect.
Fully Integrated Micromechanical Resonator Based Reference Oscillators
This project aims to achieve a fully integrated micromechanical based reference oscillator that meets or exceeds the requirements of the GSM standard. In addition to providing a highly accurate, on-chip frequency reference, a fully integrated oscillator can achieve greater stability (particularly acceleration sensitivity) and far less power consumption than any comparable off-chip oscillator. En route to achieving a fully integrated oscillator, much of the research is expected to focus on low-temperature metal processes that allow MEMS-last integration with MOS devices while retaining the stability and Q performance already offered by polysilicon counterparts.
Capacitive-Gap Micromechanical Local Oscillator at GHz Frequencies
This project aims to build a MEMS-based on-chip reference oscillator at GHz frequencies. By constructing an array of capacitive transduced micromechanical resonators with extremely small capacitive gaps and high mechanical Q, in conjunction with a low-power CMOS IC amplifier, it becomes possible to achieve self-sustained oscillation in a die-level system. While many applications for such high-frequency, low phase-noise oscillators exist, the initial goal is focused on creating a compact, low-power oscillator suitable for use in Rb atomic clock technologies. Combining with an atomic physics package, locking of the narrow linewidth oscillator to atomic transitions is possible by voltage-controlled frequency tuning via the electrostatic spring constant effect of the capacitive gaps.