Feedthrough-immune frequency tracking of electrostatic MEMS resonators
Yan, Jie
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Permalink
https://hdl.handle.net/2142/129591
Description
Title
Feedthrough-immune frequency tracking of electrostatic MEMS resonators
Author(s)
Yan, Jie
Issue Date
2025-04-28
Director of Research (if dissertation) or Advisor (if thesis)
Bahl, Gaurav
Department of Study
Electrical & Computer Eng
Discipline
Electrical & Computer Engr
Degree Granting Institution
University of Illinois Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(s)
MEMS resonator
Frequency tracking
Feed-through
Language
eng
Abstract
This thesis introduces a novel dual-tone tracking scheme for MEMS resonators. Timing references are essential in modern technology, including communication, navigation, and daily electronics. While phase-locked loops and self-sustaining oscillators are commonly used for resonator frequency tracking, MEMS resonators introduce unique challenges, such as amplitude-frequency (A-F) effects, bias sensitivity, and feedthrough, which degrade tracking performance and stability. Inspired by the Pound-Drever-Hall (PDH) technique [1], this dual-tone tracking approach effectively mitigates these issues. By leveraging dual-tone subtraction, feedthrough is eliminated, isolating the resonator’s eigenfrequency. The scheme employs frequency conversion techniques to generate an odd-symmetric error signal centered around resonance, crossing zero precisely at the target resonance frequency. This signal is used in a feedback loop to lock a voltage-controlled oscillator (VCO) to the MEMS resonator without requiring additional reference voltage. A ∼1 MHz double-ended tuning fork (DETF) resonator was tested, demonstrating real-time frequency tracking under ambient temperature variations. The observed temperature hysteresis underscores the importance of dual-mode thermometry techniques, which utilize the resonant frequency of one mode as a temperature sensor. To address this, the proposed frequency tracking scheme is also integrated into a dual-mode temperature compensation system. Additionally, experiments conducted under low bias and drive conditions confirm the effectiveness of the feedthrough-immune approach. These findings represent a promising step toward the realization of long-term stable MEMS clocks.
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