Phase-Locked Loop (PLL) Fundamentals

Phase-locked loop (PLL) circuits exist in a wide variety of high frequency applications, from simple clock clean-up circuits, to local oscillators (LOs) for high performance radio communication links, and ultrafast switching frequency synthesizers in vector network analyzers (VNA).

This article explains some of the building blocks of PLL circuits with references to each of these applications, in turn, to help guide the novice and PLL expert alike in navigating part selection and the trade-offs inherent for each different application. The article references the Analog Devices ADF4xxx and HMCxxx family of PLLs and voltage controlled oscillators (VCOs), and uses ADIsimPLL (Analog Devices in-house PLL circuit simulator) to demonstrate these different circuit performance parameters.