Oscillator PM Noise Reduction From Correlated AM Noise

We demonstrate a novel technique for reducing the phase modulation (PM) noise of an oscillator in a steady-state condition as well as under vibration. It utilizes correlation between PM noise and amplitude modulation (AM) noise that can originate from the oscillator's loop components. A control voltage proportional to the correlated AM noise is generated and utilized in a feedforward architecture to correct for the steady state as well as the vibration-induced PM noise. An improvement of almost 10-15 dB in PM noise is observed over one decade of offset frequencies for a 635-MHz quartz-MEMS oscillator. This corresponds to more than a factor of five reductions in vibration sensitivity.