Enhanced CppSim-Based Behavioral Simulator for Predicting Noise Floor and Spurs in Fractional-N Frequency Synthesizers

A fractional-N frequency synthesizer inherently generates spurious tones because its output frequency is not an integer multiple of the reference frequency. Its spectral performance is degraded by these spurious tones that are caused by memoryless nonlinearities. This paper describes a CppSim-based behavioral model which can predict the effects of a user-defined arbitrary nonlinearity in terms of noise and spurs. The simulator is demonstrated for various divider controller architectures, such as multi-stage noise shaping (MASH), successive requantizer (SR), and enhanced nonlinearity-induced noise performance (ENOP). The enhancements successfully address the limitations of the basic CppSim model and provide various interfaces for accessing data related to VCO phase noise and spectrum analysis.