a passive electro - mechanical device that reduces phase noise in oscillators , thereby improving their frequency precision . the noise reduction device can consist of a pair of coupled nonlinear resonators that are driven parametrically — by modulating their natural frequency in time , through the output signal of a conventional oscillator at a frequency close to the sum of the linear mode frequencies . above the threshold for parametric response , the coupled resonators can exhibit oscillation at an inherent frequency . the novel possibility for noise elimination is realized by tuning the system to operating points for which this periodic signal is immune to frequency noise in the drive signal , providing a way to clean the phase noise of the driving oscillator .