Low-Power MEMS-Based Pierce Oscillator Using a 61-MHz Capacitive-Gap Disk Resonator

Area of Science:

• Electrical Engineering
• Materials Science
• Physics

Background:

• Micro-electro-mechanical systems (MEMS) resonators offer miniaturization potential for electronic components.
• Traditional quartz crystal oscillators face limitations in size and power consumption for mobile applications.
• Achieving high-performance oscillators at the chip scale requires innovative circuit and resonator designs.

Purpose of the Study:

• To develop a low-power, high-performance Pierce oscillator using a MEMS wine-glass disk resonator.
• To demonstrate phase noise and power consumption suitable for mobile phone reference oscillator applications.
• To investigate the impact of MEMS resonator characteristics on oscillator performance and power efficiency.

Main Methods:

• Construction of a 61-MHz Pierce oscillator in 0.35-µm CMOS technology.
• Referencing the oscillator to a polysilicon surface-micromachined capacitive-gap-transduced wine-glass disk resonator.
• Utilizing a MEMS-enabled input-to-output shunt capacitance significantly smaller than quartz crystals.
• Analyzing circuit performance through linear circuit analysis and varying resonator bias voltage.

Main Results:

• Achieved phase noise of -119 dBc/Hz at 1-kHz offset and -139 dBc/Hz at far-from-carrier offsets.
• Demonstrated power consumption of only 3.5 mW, a 4.5× reduction over previous work.
• Obtained a 1-kHz-offset figure of merit (FOM) of -231 dB, the best reported for chip-scale oscillators.
• Further power reduction to 1.9 mW achieved by increasing resonator bias voltage.

Conclusions:

• The developed MEMS oscillator meets the stringent phase noise requirements for mobile phone reference applications.
• The novel Pierce circuit design effectively leverages MEMS resonator properties for low power and high performance.
• This technology shows promise for enabling low-power, autonomous sensor networks and embedded radios.
• Further optimization of MEMS transducer gaps and bond pad sizes can lead to even greater power reductions.