On Dependence of Amplitude Noise versus Offset Frequency in LC Oscillators

The noise spectrum of any oscillator consists of amplitude noise and phase noise. Significant fraction of the noise spectrum obtained from circuit simulations (such as periodic steady state and periodic noise analyses) may consist of amplitude noise, which is not of any significance in majority of applications of oscillators. In this paper, we present a simple method to analyze the contribution of amplitude noise with respect to phase noise in a given LC oscillator, as a function of offset frequency. The technique presented here shows that amplitude noise is suppressed at low offset frequencies and predicts the corner frequency only below which amplitude noise is negligible. Theoretical results are verified using circuit simulations.