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— Presentation at EMC Tokyo 2014 and EMC Europe 2014 —
September 24, 2014
The 2014 International Symposium on Electromagnetic Compatibility (EMC), Tokyo, was held in Tokyo from May 14th to 16th, and the EMC Europe 2014 conference was held in Gothenburg Sweden from September 1st to 4th. These two conferences are among the three most important EMC conferences worldwide this year, EMC Europe featuring as much as 250 papers and more than 500 participants from more than 40 countries.
At EMC Tokyo, Yokohama Research Laboratory (YRL) presented a paper entitled "Forward Wave Analysis for EMC Power Supply Design above 1 GHz", which was awarded with the highest conference recognition, the "Risaburo Sato Award". At EMC Europe a paper entitled "Forward Wave Analysis of Vertical Distribution of Power Supply Noise in Multilayer PCB" was presented.
Fig. 1 Forward Wave Analysis
Forward wave analysis (FWA) is an original technique developed at YRL for the EMC design of power supply planes at frequencies above 1 GHz. FWA aims at reducing the radiated electromagnetic emissions from multilayer printed circuit board (PCB) edges, which is a major cause of electromagnetic interferences among electronic equipment.
Our approach differs from the traditional one in the fact that the analysis is limited to a small region surrounding the integrated circuit (IC) whose switching is considered to be the noise source, by applying absorbing boundary conditions around the area of interest. It is an approximated technique which does not consider the effect of the power supply plane resonances and limits its target to the ratio of the radiated field before and after adding current bypass devices (e.g. bypass capacitors or ground vias), but it is extremely efficient in terms of calculation time and memory requirement with respect to commercial tools based on the traditional approach.
The rationale behind our technique is that at frequencies above 1 GHz many PCB resonances exist and an accurate estimation of the electromagnetic radiation at these frequencies is likely to fail due to the complexity of the calculation and to the lack of accurate component and source models, namely IC noise models. On the contrary, approximate calculations based on a statistical approach that neglect the details of the PCB resonances are much more feasible and suitable at these frequencies, considering also that the resonance quality factor tends to decrease with increasing frequencies.
Using FWA it is possible to improve a reference design by selecting the position of additional stitching ground vias that can reduce the far field radiation, as long as their effect is stronger than that of the PCB resonances, and by approximately estimate their effect on the radiation.
FWA is also useful in the study of the vertical distribution of the noise among PCB power supply planes, allowing considerations that correlate EMC and power integrity. For example, we have shown that the substrate layers carrying most of the power supply noise in multilayer PCBs are typically the two substrate layers adjacent to a power plane, and that ground vias are effective in reducing the radiated emissions by imposing that the electromagnetic fields in these two layers have approximately the same magnitude and opposite phase, canceling each other in the far field.
At present FWA has been verified by comparing with commercial tools for PCB analysis, and further work to confirm the results based on measurement results is still required.
(By Umberto PAOLETTI)