Conformity Magazine - February 2009 - (Page 39)

Figure 14 illustrates the radiated emission at 3 meters, and one can see that consistent radiations are detected above the 10GHz frequency value. In particular, a physical correspondence between the EM radiated field results and the S-parameters is found. The deeper resonances are detected within the frequency range 20GHz-40 GHz. This is an important point, since it demonstrates how a good design at SI level also means a good design at EMC/EMI level, and therefore fewer system-level problems. It is also evident how the field has consistent values in the small cavity section of the transceiver, especially when increasing the frequency (see Figure 14b). The field profiles help us to understand how the fields escape from a device, and allow us to focus any design modifications in the correct area. For example, at 30 GHz, the field profile shows how the magnetic field is trying to escape from the back side of the transceiver; but the point at which the field is being excited is not directly from back and/or front, but at the corner of the device. Further investigation of these output files would enable a designer to fully identify the path the field is taking, and enable corresponding design changes to be implemented. The second simulation is more challenging, due to the fact that accurate far field results in the low frequency range require an extreme large calculation domain. For this reason, a multi-level subgridding scheme (MSS) [8] is used to accurately mesh the device while keeping a relatively coarse mesh for the overall calculation domain. Figure 15 illustrates the calculation domain used to calculate the radiation, a close-up of the transceiver, and the mesh view with in evidence the MSS. Results are illustrated in Figure 16 for the three cases reported in Figure 13 (bottom view), and the following important considerations are identified. First, the optical transceiver seems to have poor shielding performance due only to the aperture located on the back side, right on the bottom panel. Second, a uniform (closed) panel seems to be unnecessary to improve the shielding performance at low frequency, since a more efficient cage panel already provides a good shielding performance, and radiation emission requirements are met. As final test case, the optical transceiver is modeled as a mounted device (see Figure 17) on a PCB whose dimensions are a=100mm (x-direction) and b=120mm (y-direction). The PCB is represented in first approximation by a simple thin sheet metal. The goal is the analysis of the radiated emissions at 3 meters in order to verify whether the presence of the PCB might generate some unexpected resonances. Figure 18 illustrates the radiated emissions 3 meters from the optical module; in this case, the predicted peak fields are Figure 13: Module with in evidence the equivalent near field source obtained by an AC analysis of the PCB february 2009 Conformity 39 http://www.captorcorp.com http://www.captorcorp.com http://www.captorcorp.com

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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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