A detailed discussion of Phase Locked Loops and its applications are presented. After defining basic building blocks, Analog PLL is taken up for detailed analysis. First and second order PLLs are thoroughly discussed and important issues of third order PLL is presented. Ability of PLL to suppress spikes in FM demodulation is shown which results in increase of FM threshold. With introduction of Digital Integrated Circuit based PLLs, Digital PLL has become very popular which differs from Analog PLL by having a digital phase or phase-frequency detector. A detailed discussion on such detectors is presented. The idea of All Digital PLL and Software PLL that offers improved flexibility, testability and other advantages are also discussed. Many interesting applications of PLL are taken up at the end. This includes Carrier recovery, Clock recovery, Frequency synthesis, Frequency and Phase Modulation etc. Both integer and fractional dividers are discussed which is useful in now popular and useful PLL based frequency synthesizers.
