Yet another spur mechanism in a charge-pump based Fractional-N PLL

摘要

Fractional-N frequency synthesizers are widely used in modern electronic systems. Their performance can be degraded by the presence of spurious tones (spurs). Many mechanisms for the production of spurs have been identified, making it possible to develop appropriate strategies to minimise or eliminate them. This paper describes another spur generation mechanism which has not been reported previously. The effect becomes important when the divide ratio is small. The robustness of the phenomenon is demonstrated using an enhanced event-driven model and validated with CppSim behavioral simulations.