Conformity Magazine - September 2008 - (Page 47)

The effect of skew in differential signals can be a source of serious electromagnetic emissions. The following tests demonstrate this effect (see Figures 21, 22 and 23). Conclusions The theoretical characteristics of the differential pair signals regarding differential and common mode noise often suggest that there will be no impact in EMI/EMC performance on the designs (that is, if there is a perfect balance in the differential signals). Good PCB design is a basic starting point to eliminate many of these problems. However, the real world implementation often experiences some level of skew, impedance mismatch, over and undershoot, etc., which is then translated into potential emissions and signal integrity problems. The intention of this article has been to illustrate alternative solutions through passive component (common mode filters) as way to minimize design cycles when the options to further improve PCB layouts become limited. Rafael Perez Magana is a product engineer for EMC technologies with TDK Corporation (www.TDK.com) and can be reached at emcsolutions@tdktca.com. References 1. LVDS Owners manual 3rd. Edition, page 9. Figure 3 in this article is reprinted courtesy of National Semiconductor High-Definition Multimedia Interface Specification, Version 1.3, by Hitachi, LTD., Matsuhita Electric Industrial Co., Ltd, Philips Consumer Electronics International, B. V., Silicon Image, Inc, Sony Corporation, Thomson Inc., and Toshiba Corporation. TDK Common Mode Filter specification sheets, TDK Corporation of America 5150 finally, a simple solution for applications 2. 3. FAST Link www.conformity.com/2160 www.schurterinc.com/new_emc first of its kind filtered AC inlet performs at high frequencies up to 1 GHz and beyond, using X2Y® technology compact modular package provides: - double shielding to ensure performance - ease of mounting and assembly - standard, medical and industrial filter versions - eco friendly design (no potting in filter casing) - approved 10 / 15 A at 250 VAC according to ENEC & cURus September 2008 Conformity 7 http://www.TDK.com http://www.conformity.com/2160 http://www.schurterinc.com/new_emc http://www.schurterinc.com/new_emc

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Conformity Magazine - September 2008 Contents Editor’s Note Commission Adopts Regulations for Internet-Based TRS Services Another Company Fined for Non-Compliance with HAC Requirements FCC Extends “Do-Not-Call” Registry Compliance Requirements Marketing Company Gets $1.4 Million Fine for Junk Faxes EU Commission Codifies Directive on TTE Market Competition EU Commission Releases Updated Standards List for the R&TTE Directive Updated Standards List for the “New” Low Voltage Directive Released New Standards List Released for the EU’s Machinery Directive The ESD Association: Voluntary Standards in Action ESD Open Forum Medical EMC Standards: Towards the 4th Edition of IEC 60601-1-2 iNARTE Informer Pre-Pulse Voltage in the HBM ESD Model Digital Interfaces and EMC Performance ESD Design Buyer’s Guide Product News Commission Publishes Updated Standards List for the EU’s Personal Protective Equipment Directive FDA Links “Human Factors” to Adverse Events with Medical Devices CPSC Actions in the News IEC Standards Update UL Standards Update Product Reviews Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - September 2008

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