A study of oscillator jitter due to supply and substrate noise

Abstract

This paper investigates the timing jitter of single-ended and differential CMOS ring oscillators due to supply and substrate noise. We calculate the jitter resulting from supply and substrate noise, show that the concept of frequency modulation can be applied, and derive relationships that express different types of jitter in terms of the sensitivity of the oscillation frequency to the supply or substrate voltage. Using examples based on measured results, we show that thermal jitter is typically negligible compared to supply- and substrate-induced jitter in high-speed digital systems. We also discuss the dependence of the jitter of differential CMOS ring oscillators on transistor gate width, power consumption, and the number of stages.