Virtual Damping in Oscillators

D. Ham and A. Hajimiri

This paper presents a new point of view of oscillator noise, bringing transparent insight into the phase noise. This work bridges fundamental physics of noise and existing oscillator phase noise theories and reveals the direct correspondence of phase noise and the Einstein relation. The concept of virtual damping is presented utilizing an ensemble of oscillators as a measure of phase noise. The explanation of the linewidth narrowing through virtual damping results in a clear de¯nition of loaded and unloaded quality factors of an oscillator. The validity of this new approach is verified by excellent experimental agreement.