Fully Balanced Differential Micromechanical Resonator Reference Oscillator

A 61-MHz MEMS-based low-phase noise reference oscillator comprising a micromechanical capacitive-gap-transduced polysilicon wine-glass disk resonator and a custom fully balanced differential transimpedance amplifier (TIA) integrated circuit in 0.18-µm CMOS achieves a 5-dB phase noise figure of merit (FoM) improvement over a comparable single-ended reference oscillator [1]. Key to this improvement is fully balanced differential operation of both the resonator and the sustaining amplifier, which rejects not only common mode circuit and supply noise, but also resonator DC-bias (VP) noise. As a result, this 61-MHz oscillator achieves phase noise marks of -111, -129, and -132 dBc/Hz at 1, 10, and 100-kHz offsets, respectively, while consuming only 140 µW of power to achieve an oscillator phase noise FoM of -215 dB.