Analysis of spread-spectrum clocking modulations under synchronization timing constraint

Abstract

Spread spectrum clocking slowly sweeps clock frequency of a digital system to reduce the Electromagnetic Interference (EMI). In a digital system-onchip there can be subsystems where clock spreading is not allowed. This paper analyzes the performances achievable by spread spectrum clocking when a constraint is imposed to easily synchronize clock modulated and unmodulated subsystems. It is shown that the best modulation gain (7.7 dB) is achieved by using optimized discontinuous modulation.