Phase‐locked Loops

Abstract

Phase‐locked loops (PLLs) are used everywhere in information and communication technology (ICT) and measurement engineering to implement various applications such as modulators and demodulators, frequency synthesizers, and clock recovery circuits, just to mention a few examples. Depending on the operation principle of their building blocks, analog, digital, and hybrid‐type PLLs are distinguished. This article starts with the analog PLL theory in order to introduce the PLL terminology and analysis, and then it discusses the theory and implementation of more complex PLL configurations such as zero‐crossing digital, sampling, and charge‐pump PLLs. Because the key PLL building block is the phase detector, its variants are also analyzed. Finally, the various PLL applications are surveyed.