Parametric filtering surpasses resonator noise in ALN contour-mode oscillators

In this work we present a new method to lower the phase noise in acoustic resonator based oscillators. This method uses the nonlinear dynamics of a parametric divider made to work close to the bifurcation region. We call this technique "parametric filtering". This approach was applied to an oscillator based on an aluminum nitride contour-mode resonator vibrating around 227 MHz. This class of resonators exhibits frequency flicker noise that limits the oscillator phase noise close to the carrier. By means of parametric filtering we obtained an improvement in the phase noise of more than 14 and 19 dB, respectively at 1 and 10 kHz offsets. This technique can be applied to any MEMS oscillator and represents the first demonstration of open loop phase noise filtering.