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• Engineering Implementation of High Performance PCB Design
• 来源：EDADOC     作者：Hans Axiao Bridge Tang     发布时间：2008-07-23 08:12:01    评论(0条)  
  

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• 6.Challenges of EMC

  In an age when people have an increasing standard of living and pay close attention to environmental protection relevant to electromagnetic pollution etc, EMC problems have become part of research and development for all of the electronic products. As a “Black Magic”, EMC problems tend to give more trouble to engineers. 
    
  EMC has to be given consideration to at the headstream. As the headstream of EMC of products , EMC performance of PCB has been paid more attention to. Among many EMC indices, RE is the most difficult for hardware engineers to deal with.

  Due to restrictions of model, even top-class EMC simulation software can not provide the data comparable with the actually-tested data. Therefore, only some simplified distribution conditions of radiation fields of single radiation source under some special circumstances can be provided for reference.  
   
  So far, EMC design is still dependant on the experience of EMC engineers or hardware engineers. For engineering design, we have to possess some commonly-used experience about engineering design without having to carry out too much theoretical analysis. Meanwhile, we should use the assistant method such as near-field EMI probes etc to solve EMC problems. The above drawing refers to the distribution drawing of RE indices and specific frequencies measured by the near-field probe.

  In the author’s opinion, with regard to EMC problems in PCB, close attention should be paid to the following three aspects:

  1)Power supply
  2)Clock signal (and other high radiation sources)
  3)Interface circuit

  For power supply, the integrity of power supply (ground) and the design of power ground as the return path should be taken into account;

  The clock as the main EMI source of board contributes more than 60% to EMI;
  All efforts for EMC design of the product may be wasted even if only one interface is not well designed.

  Comply with the above-mentioned three points, the EMC problems will be understood and solved.
  

  
  
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