Abstract
Self-sustained feedback oscillators referenced to MEMS/NEMS resonators have the potential for a wide range of applications in timing and sensing systems. In this paper, we describe a real-time temperature compensation approach to improving the long-term stability of such MEMS-referenced oscillators. This approach is implemented on a ~26.8 kHz self-sustained MEMS oscillator that integrates the fundamental in-plane mode resonance of a single-crystal silicon-on-insulator (SOI) resonator with a programmable and reconfigurable single-chip CMOS sustaining amplifier. Temperature compensation using a linear equation fit and look-up table (LUT) is used to obtain the near-zero closed-loop temperature coefficient of frequency (TCf) at around room temperature (~25 °C). When subject to small temperature fluctuations in an indoor environment, the temperature-compensated oscillator shows a >2-fold improvement in Allan deviation over the uncompensated counterpart on relatively long time scales (averaging time τ > 10,000 s), as well as overall enhanced stability throughout the averaging time range from τ = 1 to 20,000 s. The proposed temperature compensation algorithm has low computational complexity and memory requirement, making it suitable for implementation on energy-constrained platforms such as Internet of Things (IoT) sensor nodes.
Highlights
Stable oscillators are vital for precision timekeeping in various applications, including wired and wireless communications, positioning, navigation, and sensing
Oscillators referenced to micromachined resonators [2–5] are promising alternatives due to their small form factors, low phase noise thanks to high Q, low power consumption, good long-term stability, compatibility with batch processing, high reliability, low cost, and wide operating temperature range
Further improvements in long-term stability can be obtained by replacing temperature compensation with temperature control (i.e., implementing an oven-controlled oscillator (OCO)) and/or by locking the oscillator to an external frequency reference such as GPS over long time scales [34,35]
Summary
Stable oscillators are vital for precision timekeeping in various applications, including wired and wireless communications, positioning, navigation, and sensing. Oscillator stability against temperature variations and fluctuations is critical for many of these applications [1,2]. Temperature-compensated quartz crystal oscillators provide excellent stability versus temperature, and have dominated the timing and frequency control market for decades. They are not suitable for monolithic integration with CMOS circuitry, which makes them sub-optimal for emerging applications such as mobile devices and IoT nodes, where miniaturization is important for reducing cost. Oscillators referenced to micromachined resonators [2–5] are promising alternatives due to their small form factors, low phase noise thanks to high Q, low power consumption, good long-term stability, compatibility with batch processing, high reliability, low cost, and wide operating temperature range. Aedveenmru,otmnhsebtreealrateosdtficctohpmeroeppxeecrnetlsileaestniotofnsShimoarrete-thods havesbtreoennglryepteomrtpeedraftourreim-deppreonvdinengt,tesmo pteemrapteurraetusrteabfliulicttyua[t2i,o6n–s13d]e.gFraodreexthaemlpolneg,-tienrm[12f]r,etqhueenacuythors implesmtabeinlittya poaf sSsii-vbeasceodmopsecnilslaattoiorsn. mAetnhuomdbbeyr uoftilciozminpgesnisliactoionndmioextihdoeds(SihOav2e), wbeheinchrehpaosrtaendofpopr osite
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