Fraetional-N synthesizers are subject to generation of undesired spurious energy due to both linear and nonlinear processes. Previously, we presented an accurate modeling of the nonlinear, time-varying nature of the phase frequency detector (PFD), charge pump and frequency divider . The proposed modeling technique was able to predict in-band spur power levels within 1.8 dB accuracy. In this paper we demonstrate using the proposed model that the close-in phase noise increase due intermodulation of the ΣΔ high frequency quantization noise is independent of the synthesizer reference frequency, which is in contrast to commonly used linear models. A behavioral model is also used to show that the more detrimental near-integer in-band spurs can be generated by cross-coupling between the synthesizers's various building blocks.