Evaluating & Designing Around Specification Requirements

Craig is also an iNARTE Certified EMC Laboratory Engineer and author of several papers for the IEEE EMC Symposium.  Finally, as a member of SAE EMI and EMR Committees, as well as a US National Committee technical advisor for CISPR-D, our EMC Lab Manager undoubtedly likes to stay active in the EMC community.

Nothing is worse than going to the EMC lab and failing an emission test. This is especially true when you figure out that an operating frequency of the Device Under Test (DUT), that you designed, is causing excessive emissions within a frequency band which has a low limit. We see this time and time again in the test laboratory.

The best way to prevent this from happening is to evaluate the specification requirements before you start picking out clock frequencies and communication rates. If you look at the specification limits before you design, or during the design phase, you can determine frequencies that you should stay away from. Don’t select operating frequencies that fall into frequency bands with low emissions limits. Also look at the harmonic frequencies (especially the odd harmonics of the operating frequency) to see if a harmonic will fall into a frequency band with low limits. If possible, pick operating frequencies that fall into frequency bands with higher emissions limits.

Many times communications rates can be adjusted through firmware. This is something that can be in your “bag of tricks” when designing the product and/or troubleshooting a failure. When it comes to designing for good EMC performance…review and design to the specification. If you do, this will save a lot of future headaches and re-design costs.

Do you have any questions about CISPR Emissions Testing, Design, or other related topics? Share your comments or questions below and our expert, Craig Fanning, will get back to you. 

Craig is also guest-presenting a webinar, "EMC for Vehicles: Truly Mobile Electronics", with Washington Labs on Thursday, August 15, 2013.  Please follow the link if you would be interested in learning more.