A novel and accurate nonlinear model to estimate the settling time of charge-pump based frequency synthesizers is presented. The correlation between the synthesizer lock time and the linear detection range of the phase-frequency detector is extensively investigated. An accurate analytical expression for the settling time of the frequency synthesizer is derived, showing less than 5% error compared to the presented state-space model.
['Tord Johnson', 'Johnny Holmberg']
Nonlinear state-space model of charge-pump based frequency synthesizers