Abstract
This paper reports on the design and implementation of a low power MEMS oscillator based on capacitively transduced silicon micromachined resonators. The analysis shows how design parameters of MEMS resonator impact on the power requirement of the oscillator, particularly with a view towards informing the impact of device and interface parasitics. The analysis is based on resonators fabricated in a 2-μm gap SOI-MEMS foundry process. The sustaining circuit, which is based on a Pierce topology, is fabricated in a standard 0.35μm process. An automatic gain control (AGC) is adopted to suppress the mechanical non-linearity so as to improve oscillator frequency stability. The 110-kHz MEMS and CMOS dies are assembled within a standard ceramic package and electrically integrated through wire bonds. The oscillator core consumes 400nA (900nA with parasitic readout loading) at 1.2-V dc supply while demonstrating a frequency stability of less than 0.5ppm. The work provides a thorough analysis and design guidelines for both MEMS and CMOS circuit design with a view towards minimizing overall power consumption. The implications of the results reported in this paper are towards enabling a new class of low power resonant MEMS sensors that utilize the oscillator as a front-end building block.
Highlights
Micromachined resonant sensors have been researched for several decades due to the advantages inherent in chip-scale integration and dimensional scaling [1]
The capacitive MEMS oscillator based on a Pierce topology [11] previously implemented for real-time clocks utilizing MEMS resonators [12,13] with low-power consumption were demonstrated, though detailed design analysis was not provided
This paper reports on the comprehensive analysis and implementation of an oscillator circuit in standard CMOS as a low power front-end circuit interface for micromachined resonant sensors that addresses the power minimization criterion
Summary
Micromachined resonant sensors have been researched for several decades due to the advantages inherent in chip-scale integration and dimensional scaling [1]. The capacitive MEMS oscillator based on a Pierce topology [11] previously implemented for real-time clocks utilizing MEMS resonators [12,13] with low-power consumption were demonstrated, though detailed design analysis was not provided. This paper reports on the comprehensive analysis and implementation of an oscillator circuit in standard CMOS as a low power front-end circuit interface for micromachined resonant sensors that addresses the power minimization criterion. The detailed analysis would help both the MEMS and circuit engineers to design a power-optimized capacitive MEMS oscillator based on the availability of the process. Double-ended tuning fork resonators operating in this frequency range have been previously integrated into a variety of device applications addressed above, and the results reported in this paper potentially have wide device applicability.
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