Mechanically-coupled micromechanical resonator arrays for improved phase noise

Reductions in phase noise by more than 26 dB have been obtained over previous micromechanical resonator oscillators by replacing the single resonator normally used in such oscillators with a mechanically coupled array of them to effectively raise the power handling ability of the frequency selective tank by a factor equal to the number of resonators used in the array, and all with virtually no increase in volume or cost, given that all resonators are integrated onto a single die using batch processed MEMS technology. Specifically, a mechanically coupled array of ten 15.4-MHz 40μm×10μm×2μm free-free beams embedded in a positive feedback loop with a single-ended to differential transimpedance sustaining amplifier achieves phase noise of -109 and -133 dBc/Hz at 1 kHz and far-from-carrier offset frequencies, respectively. When divided down to 10 MHz, these effectively correspond to -112 and -136 dBc/Hz, respectively, which represent more than 17 and 26 dB improvements over recently published work with clamped-clamped beam resonator oscillators.