Series-resonant VHF micromechanical resonator reference oscillators

Series-resonant vibrating micromechanical resonator oscillators are demonstrated using a custom-designed single-stage zero-phase-shift sustaining amplifier together with planar-processed micromechanical resonator variants with quality factors Q in the thousands that differ mainly in their power-handling capacities. The resonator variants include two 40-μm-long 10-MHz clamped-clamped-beam (CC-beam) resonators, one of them much wider than the other so as to allow larger power-handling capacity, and a 64-μm-diameter 60-MHz disk resonator that maximizes both Q and power handling among the resonators tested. Tradeoffs between Q and power handling are seen to be most important in setting the close-to-carrier and far-from-carrier phase noise behavior of each oscillator, although such parameters as resonant frequency and motional resistance are also important. With a 10× higher power handling capability than the wide-width CC-beam resonator, a comparable series motional resistance, and a 45× higher Q of 48 000, the 60-MHz wine glass resonator reference oscillator exhibits a measured phase noise of -110 dBc/Hz at 1-kHz offset, and -132 dBc/Hz at far-from-carrier offsets. Dividing down to 10 MHz for fair comparison with a common conventional standard, this oscillator achieves a phase noise of -125 dBc/Hz at 1-kHz offset, and -147 dBc/Hz at far-from-carrier offsets.