Investigation of Noise Transfer Characteristics of Phase-Locked Loop Using Sallen Key Low Pass Filter

To improve the performance and to reduce the errors caused by limited bandwidth in Phase locked loop, we proposed a method for modeling and simulation by usingSallen-key low pass filter with compensation methodology. The noise transfer functionis estimated, and simulation is performed for two different filter sections as a loop filter in the phase locked loop, namely: (i) idealSallen-key low pass filter, and (ii) compensated Sallen-key low pass filter. The complete simulation program for the proposed model is implemented in MATLABfor analysis. The characteristics of the system namely: (a) phase margin, (b) damping factor, (c) delay margin, and (d) stability, are studied with the help of Bode and Root locus plots. The propose model is found to be stable. The damping factor, phase margin and delay margin of the model is found to be 1, 86° and $0.524\boldsymbol{\mu}\mathbf{s}$ respectively.