6. Introduction to second order type – I PLL

Abstract

From the analysis of the first order loop, presented in Part I, it becomes evident that the presence of the ripple in the output of the phase detector is the main source of unwanted behaviour. In specific, the ripple is responsible for the manifestation of parametric resonance effects, which increases the amplitude of the VCO. In addition, the ripple carries information about the time delay, which manifests itself in the loop. As it is known, part of the time delay comes from the unmodeled dynamics of the loop components and is due to manufacturing defects or deviation of the VCO dynamics from the dynamics of the second order system (e.g. third or higher order). In other words, the ripple reveals the unwanted dynamic behaviour of the loop components.