如何识别来自PLL的相位噪声

如何识别来自于PLL的相位噪声Applied Radio Labs
www.radiolab.com.au

Identifying Phase Noise Sources in a PLL
Design File: DN002 15 October 1999

Introduction
Many modern communication systems utilise PLL frequency synthesizers, commonly with specifications on phase noise performance. This report details a simple technique that we have found valuable in isolating the sources of phase noise in a PLL synthesizer, and is especially useful when only a spectrum analyser is available for measurements. An additional passive filter (which we nicknamed a “PLL Widget”) is added to the PLL, greatly narrowing the loop bandwidth, causing the output phase noise to approximate that from the VCO alone. Inspection of the output phase noise in the normal and reduced bandwidth modes enables the source of the phase noise to be tracked do