Conformity Magazine - March 2008 - (Page 49)

n order to comply with the stringent radiated emission limits imposed by the standards, and taking into account the increasing clock speed and data rates of current highspeed digital electronics, it is often necessary to shield the enclosure where the printed circuit board (PCB) is located. A thorough electromagnetic compatibility (EMC) or signal integrity (SI) assessment of a complete board or system is often a daunting task, due to the extreme complexity of modern electronic systems. But system designers would like to accurately evaluate the electromagnetic interference (EMI) produced by high-speed signals and, at the same time, to address the regulations due to the EMC community. This capability is useful in predicting and correcting interference problems at various stages in the design process. There are several requirements for an accurate evaluation of these effects. First, the complicated multilayered board and package structures used in today’s designs (including signal traces, supply planes and vias) must be modeled in a way that takes into account full-wave effects. Secondly, the behavior of various shielding structures (such as metallic enclosures) must be taken into account as well. Finally, the issue of problems consisting of small structures embedded in large computational domains must be addressed. Performing such analysis is often a computational challenge. A three dimensional (3D) solver is desirable for modeling the arbitrary shapes of the enclosures (which often includes slots, apertures [1]), but simulating a multi-layer board or package can be difficult and memory consuming. The principle problems result from the high complexity of modern boards and packages, and the 3D nature of the system enclosures surrounding them. This problem can be solved by using either of the following approaches: 1. A specialized 2D solver (transmission line (TL), cavity model [2]), 3D quasi-static (partial element equivalent circuit (PEEC) [3] or 2D FDTD [4]) can be employed to compute the current distribution on the power (PWR) plane of a complex PCB or the Nearfield of the entire board [4]. A full-wave 3D EM solver (finite integration technique (FIT) [5] or transmission line matrix (TLM) [6]) can be instead used to analyze the shielding performance of a metallic enclosure due to the calculated current/near field distribution. I a rectangular box 30 x 12 x 30 cm in size, with a rectangular aperture of 10 x 0.5 cm in size, located at the center of the frontal wall (15, 6, and 0). The enclosure is illuminated by a normal incident plane wave (farfield source) at 0 degree polarization, and three probes are placed in the center position inside the enclosure in order to register the three components of the electric field (Ex, Ey, Ez) and to calculate the SE afterwards. Figure 1: Typical EMC-EMI workflow analysis 2. The described workflow is illustrated with the different steps in the block diagram of Figure 1. Model Validation An important point is to check the reliability of the software used for both the numerical simulations. For example, Figure 2a illustrates a simple enclosure model (already studied in [7]), marCh 2008 Conformity 9 http://www.ddbunlimited.com http://www.ddbunlimited.com

Table of Contents Feed for the Digital Edition of Conformity Magazine - March 2008

Conformity Magazine - March 2008 NewsBreaks Editor's Note Adelstein Renominated to the FCC Industry Canada Publishes FAQs On RF Fields FDA Gives Its Scientific Capabilities Poor Marks FDA Offers Guidance On its Product Review Process FDA Publishes Updates to List of Recognized Standards FDA Warns of Patient Risk From Electric Dental Handpieces Complying with the EMC Directive, Second Edition ESD Open Forum Emerging Issues in Standards - Korean "RoHS": Not Like RoHS at All The iNARTE Informer Challenges in Testing - Field-Induced Charged Device Model: What Really Happens Design Fundamentals - EMI Shielding Technologies for Consumer Electronics Equipment Focus On...Compliance Software Buyer's Guide Additional Standards Published for the EU's ATEX Directive Additional Standards for the EU's Medical Devices Directive Also Published China to Require Bar Codes to Enhance Product Safety CPSC Releases 2007 Self-Assessment CPSC Actions in 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 - March 2008

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