What PNN Says About Spur Rolloff Rates in MASH-Based CP-PLLs With Polynomial Distortion

Interaction between the quantization error that the multi-stage noise shaping (MASH) digital ∆Σ modulator (DDSM) introduces into the system and nonlinear distortion in the loop generates fractional spurs. The Periodic Nonlinearity Noise (PNN) concept can be used to predict the locations and amplitudes of fractional spurs. This paper presents additional insight offered by PNN relating to the impact of the order of the MASH and the order of the polynomial distortion on the rolloff rate of the integer boundary spur (IBS) family.