Conformity Magazine - February 2009 - (Page 30)

Challenges in Testing by A. Ciccomancini Scogna PhD, CST of America, Inc. and S. Zimin PhD, Finisar Corporation he existing electromagnetic interference (EMI) design and verification techniques are mostly measurementorientated strategies, utilizing conventional approaches such as shielding, grounding, power decoupling, and placing absorbing materials. A good EMC design process and evaluation in an earlier stage of a product design chain can significantly reduce the design cycle and better mitigate the EMI and radio frequency interference (RFI) problems from the sources. However, it is well known that current electromagnetic modeling algorithms and a standard computer face great challenges when predicting EMI for a full computer system (desktop or notebook). On the other side, when the electrical size of the device under test (DUT) is small, other problems arise (such as high aspect ratio), and therefore presents problems in numerically resolving tiny features which may consistently affect the EMC/EMI of the device. Although great progress has been made on computational electromagnetic and computer capabilities, it is still extremely challenging to model a running computer to predict its platform noise and EMI/RFI in a straightforward approach, such as method of moment (MoM), finite difference time domain method (FDTD), or finite element method (FEM) [1]. Furthermore, new faster IO interface introductions such as PCI-Express generation II requires more meshes in the computational domain in order to cover fine “electrically large” geometry, resulting in more memory and computation time requirements. Therefore, a new methodology which can reasonably predict EMI with modest computer memory requirements and running time is very desirable for platform designers. The goal of the present article is to present a simulation 30 Conformity february 2009 T methodology to study the EMI/RFI impact of highperformance printed circuit boards (PCBs) and their radiated emissions in a complex system environment in an early design phase before a prototype has been manufactured. The near-field electromagnetic field distribution is generated from the system level simulation of the PCB, with given excitation sources inside the system, or with the switching signal launched on the traces. The current distribution on all surface traces for the entire PCB and the edge field distribution along the edges of the board are simulated first, and then the near field distribution is calculated from those current distributions. Once the near field distribution is generated, it can be exported as the equivalent surface current sources for a next level three dimensional (3D) EMI simulation which, for instance, can be the system level EMI/EMC analysis of a chassis (enclosure) with PCBs inside. The major analysis steps can be summarized as: 1) obtain the near field distribution from the board/package simulation using specialized tool time and/or frequency domain solver (typically not full-wave); 2) export the equivalent surface current distribution based on the near field distribution; and 3) calculate 3D field distribution in a next level using a 3D full wave solver. The article is organized as follows. In the next section, the proposed simulation strategy is briefly described along with an example of a complex PCB inside a simple metallic enclosure. In particular, two different numerical methodologies are applied to study the EMC/EMI performance of the metallic enclosure by highlighting advantages/disadvantages. Then, the strategy is applied to study the EMC/EMI of a real high speed data communication optical transceiver. Important considerations will be addressed at both SI and EMC/EMI level. © Milan Surkala | Dreamstime.com Efficient Methodology for the EMI Analysis of Optical Transceivers Including PCBs and/or Flex Circuits

Table of Contents Feed for the Digital Edition of Conformity Magazine - February 2009

Conformity Magazine - February 2009 Contents Editor's Note FCC Clarifies Closed Captioning Requirements for DTV Receivers Commission Cracks Down (For the Fifth Time!) On Junk Fax Marketer FDA Requests Comments on Global Harmonization Documents Australia Now Requires Solar Panel Testing and Certification EU Drafting New Directive on Toy Safety EU Commission Revises Standards List for EMC, R&TTE Directives Additional Standards Published For the EU's Medical Devices Directive EU Commission Publishes Additional Standards for Directives on Active Implantable, In Vitro Medical Devices EMC For the Functional Safety of Automobiles ESD Open Forum The ILAC Arrangement: Facilitating Trade Efficient Methodology for the EMI Analysis of Optical Transceivers Including PCBs and/or Flex Circuits The EuP Directive - Implementation, Design Requirements and Issues Chambers, Shielding, and Accessories Buyer's Guide CPSIA Lead Requirements Apply to Existing Inventory, Says CPSC CPSC Clarifies Certifcation Requirements Other CPSC Actions in the News IEC Standards Update Product Reviews UL standards Update Telcordia Standards Update From Our "You Can't Make This Stuff Up" Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - February 2009

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