AMD 30925 manual EMI Reduction Techniques, EMI Emission Standards, Spread Spectrum Clocking

30925 Rev. 3.04 February 2004	Builder’s Guide for AMD Opteron™ Processor-
	Based Servers and Workstations

Chapter 6 EMI Reduction Techniques

These electromagnetic interference (EMI) reduction techniques can be implemented with relatively short lead-times at the final system-assembly stage. Proper electromagnetic compatibility (EMC) and motherboard design techniques are assumed.

The effectiveness of all the EMI-reduction techniques varies from system to system. This chapter is provided as a guideline only, to help identify and close the common EMI energy paths that allow radiated emissions to escape from the chassis enclosure.

6.1EMI Emission Standards

EMI emissions from a computer system must be controlled and kept below regulatory limits. Radiated EMI emissions are measured with an antenna, typically 10 meters away from the computer system under test. There are different EMI standards for systems marketed in the United States and Europe, and all standards are continually updated. Typically, most computers must meet FCC Class “B” for the US and CE Class “B” EMI requirements to be sold in Europe.

6.2AMD Opteron™ Processor-Based System Builder EMI Reduction Techniques

This document describes system-level EMI reduction techniques based on past successful problem resolution of EMI radiated emissions. All the techniques described may be able to be implemented at the final system assembly stage with relatively short lead-time. This document does not contain long lead-time techniques involving motherboard re-layout or chassis sheet metal redesign. Proper up-front electromagnetic compatibility (EMC) motherboard design techniques are assumed. For more information on these techniques, please refer to the AMD Athlon™ 64 FX and AMD Opteron™ Processors Motherboard Design Guide, order# 25180.

The effectiveness of the following EMI reduction techniques varies among different computer systems. EMC engineering tests must be performed to determine how effective each of the following EMI reduction techniques is for a particular system.

This list of EMI reduction techniques is numbered in the recommended order of evaluation and relative simplicity. Each item is described in detail for clarity.

1. Spread Spectrum Clocking

AMD processors are designed to run with spread spectrum clocking enabled. Ensure that the motherboard BIOS has enabled the spread spectrum feature of the system clock generator. Enabling the spread spectrum setting often lowers frequency amplitudes by more that 5 dB.

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