ALTPLL (Phase-Locked Loop) IP Core User Guide

ID 683732
Date 6/16/2017
Document Table of Contents

Spread-Spectrum Clocking

Spread-spectrum technology reduces electromagnetic interference (EMI) in a system. This technology works by distributing the clock energy over a broad frequency range.

The spread-spectrum clocking feature distributes the fundamental clock frequency energy throughout your design to minimize energy peaks at specific frequencies. By reducing the spectrum peak amplitudes, the feature makes your design more likely meets the EMI emission compliance standards, and reduces costs associated with traditional EMI containment.

The traditional methods for limiting EMI include shielding, filtering, and using multi-layer printed circuit boards. Multi-layer circuit boards are expensive and are not guaranteed to meet the EMI emission compliance standards. The use of spread-spectrum technology is simpler and more cost-effective than these other methods.

To use the spread-spectrum clocking feature, you must set the programmable bandwidth feature to Auto.