A Real-Time Automatic Stability Optimization Loop (SOL) for MEMS-Referenced Oscillators

The frequency stability of local oscillators (LOs) based on micro- and/or nano-mechanical resonators integrated with CMOS-based circuitry is a key performance limiter for ultra-low-power reconfigurable wireless architectures. This paper proposes a software-defined automatic stability optimization loop (SOL) that optimizes the stability of such LOs by finding and tracking their maximum stability points (MSPs). The technique enables automatic minimization of either frequency- or time domain oscillator stability metrics such as phase noise or Allan deviation (ADEV) in the presence of external perturbations. The SOL accomplishes this goal by using a perturb-and-observe (P & O) algorithm to lock the operating point of the oscillator at one of its MSPs. The proposed approach was experimentally verified on a MEMS-referenced oscillator realized using a single-crystal silicon (SC-Si) comb-drive resonator connected in feedback around a highly tunable single-chip CMOS sustaining amplifier.