Noise suppression in injection-locked ring oscillators

Presented is a study of the optimal injection frequency using a time-domain model as a technique to improve the noise suppression in injection-locked ring oscillators. It is found that offsetting the injection signal frequency by roughly half of the one-sided lock range relative to the free-running oscillator frequency can lead to higher noise-suppression bandwidth and lower phase noise. Applied to a five-stage ring oscillator, the model shows good agreement with simulations, which indicate that the optimal injection frequency increases the noise-suppression bandwidth by up to 5×, and lowers the phase noise by 15dB.