Phase-locked loops (PLL) are used extensively throughout modern electronic systems. In data communication systems, PLLs are used in transmitter clock multipliers and receiver clock recovery circuits. A key performance factor for the PLL is how they manage jitter. A critical PLL metric is the jitter transfer function which is based on the PLL loop bandwidth. There are several measurement methods that can be used to characterize PLL loop bandwidth and jitter transfer. When operating on digital data signals, PLL bandwidth can vary with the data pattern. In this article, Greg Le Cheminant, Keysight Technologies, focuses on test methods that allow operation on data rather than only clock signals provide very high precision and useful insights into PLL behavior.
