Conformity Magazine - February 2009 - (Page 32)

Simulation Strategy Near-field scanning systems have been widely used to infer properties of the electric and magnetic fields surrounding integrated circuits (IC) and circuit boards. For instance, nearfield measurements are often taken in the vicinity of a DUT for computing its near/far-field patterns. Near-field scanning above an IC chip has been used to analyze the current distribution over the chip package. This information may be helpful in diagnosing EMI problems created by sources on the chip. However, the mechanical configuration of these systems makes it difficult to perform similar measurements when the radiating circuits are surrounded by an enclosure. The approach being considered here is one that uses scanning simulations of the near-field to construct an equivalent surface current distribution. It includes two major steps. The first step determines an equivalent surface current distribution from the near-field scanning simulation data obtained by means of a dedicated solver. The second step predicts the near- and far-field from 3D numerical simulations, with the original radiating antenna replaced by an equivalent current and nearby near-field geometries included. The equivalent current source approach provides a means of calculating the radiated fields from nearfield data. In this approach, an equivalent electric/magnetic current determined from near-field measurements replaces the radiating antenna by using the equivalence principle. Once the equivalent current is determined, the correct near- and far-fields of the radiating antenna can be calculated directly from this equivalent current under certain assumptions [2-5]. Figure 1 illustrates the PCB used to test the proposed methodology. It consists of four layers with multiple nets and memory chips mounted on top of it. A 3D EM simulation of the full board would obviously require a consistent amount of time to set up the model, and it would also be necessary to have a relevant amount of processing memory. For these reasons, a quasi-static (3D) partial element equivalent circuit (PEEC) method (provided by a proprietary software application [6]) is used to simulate the PCB. The PEEC method is really an advantage for this kind of numerical simulations. It provides as a natural response a SPICE equivalent circuit; therefore, multiple nets/ layers selection can be easily done, and it is optimized to use less memory when the all nets are not included. From an EMI radiation point of view, there is no need to simulate the complete board with all the nets, since the effect due to the not-excited net is important for crosstalk analysis, but negligible when studying the radiation effect due to the board within a metallic enclosure. On the other side, the presence of the PWR/GND layers is important to take into account, since the calculated surface current distribution (as well as the near-field) is different whether the physical dimensions of the layers wouldn’t be taken into account. In order to validate the proposed Figure 1: Top view of the PCB used to test the proposed methodology a b Figures 2a and 2b: PCB model, equivalent surface for the E/H calculation and E filed at 0.5GHz and 1GHz. 32 Conformity february 2009

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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