Comparison of phase noise models on a class of ring oscillators using low voltage swing fully differential delay cells

Abstract

This paper compares the phase noise models on a class of differential saturated ring oscillator with low voltage swing. Variance parameter/single stage jitter is used as the metric for comparison. When first passage time (fpt) is employed, first for the simple case of the RC representation of the differential pair, an exact expression involving the parabolic cylinder function is used in this comparison. Then for the general case, the expression using time scaling is used for comparison. On the last passage time (lpt) model, the probability distribution function (pdf) of lpt is used to further differentiate the models. The fpt part in the complete lpt pdf is identified. Comparison of the phase noise's power spectral density expression is then presented. The phase noise expression of this author does not go to infinity as offset frequency approaches zero. Finally simulation results on example designs are presented, where it is shown that the model by this author, when compared to other models, can improve accuracy by 7-10 dBc/Hz.