Prediction of the impact of substrate coupled switching noise on frequency synthesizers

Abstract

This paper proposes a methodology to accurately predict the phase noise effects in frequency synthesizers as a consequence of switching noise coupled through the substrate. The method proposed is based on a phase model of a frequency synthesizer where each circuit block is characterized by complex noise sensitivity functions. Considering the phase information of the different contributors allows to evaluate the noise without overestimation, as well as identifying the main noise contributors. This information can then be used by designers to decide where to put the effort to mitigate the noise effects. The methodology is applied to a typical N-Integer frequency synthesizer based on a LC-VCO. Measurements on this frequency synthesizer implemented in a 0.35 μm CMOS technology have provided information of the relative importance of the noise aggressors, the effect of the loop on the phase noise, as well as comparison to the predictions obtained with the proposed methodology.