Resonators driven to self-oscillation via active feedback play an impo
rtant role in technology. Among the stochastic processes driving phase
diffusion in such oscillators is noise from the feedback amplifier. H
ere a technique is described by which phase diffusion due to this nois
e can be suppressed. We have achieved a 10 dB reduction in phase diffu
sion by using the technique on an oscillator whose frequency-controlli
ng element is a nonlinear mechanical resonator. The technique, in prin
ciple, provides a quantum nondemolition method of tracking a resonator
's phase.