Modeling And Simulation Of Fractional Frequency Synthesizer

In this work, the modeling and simulation approaches of delta-sigma fractional-n (Δ-ΣPLL) frequency synthesizer is closely discussed, including two different field of models: linearized modeling and behavior modeling.One expression of transfer function for mixed signal system is firstly proposed in this work, based on discrete time and continuous time signal processing theory, which could be employed on the study and analysis on the practical mixed-signal system, such as PLL and MDLLSecondly the linearized model of a second order charge pump PLL is discussed. And the focus is on the linearized model of PFD module, some approaches is adopted for arriving at a mathematic deduction for the linearized process based on several definite assumption. Further, the extent of approximation is discussed.The rest part of this work is based on one set of PLL design assistant toolbox developed by the author, and is focus on the dynamics analysis and behavior modeling of 2nd orderΔ-ΣPLL. The dynamics analysis is based on the foregoing mixed signal system transfer function expression and linearized modeling approaches, obtaining the system transfer function of a 2nd orderΔ-ΣPLL. Hence, the methodology of system specs, parameters calculation and optimization of settling time and noise performance, is discussed.Finally, the behavior model proposed in this work, is developed in Matlab, which could perform cycle-wise behavior simulation of a 2nd orderΔ-ΣPLL. The nonlinearity of charge pump, VCO and SDM is covered by this model, which results in a accurate settling time simulation.