EMI Sub-System Emission Limits Based on Statistic Analysis
09 July 2007
Product EMI pre-compliance evaluation becomes even more important nowadays than before due to the growing industrial trend in outsourcing and OEM. Pre-compliance testing involves measuring the radiated and power port conducted emissions of a complex system at the unit, shelf and/or sub-system levels. Defining the appropriate EMI limits at the sub-system level is crucial for the compliance of the overall system. The suppliers rely on the product specifications to design their products. If the sub-system level limit specified is too conservative, the product would be over designed and the cost would go up. However, if the sub-system level limit specified is too loose, the system EMI compliance will be in jeopardy. This paper utilized the statistical modeling recommended by ITU [1] to estimate the maximum increase in the radiated and power-line conducted emissions from a multi-unit system. The results are useful in determining appropriate product sub-system level EMI limits and enhancing engineers' judgment for compliance evaluation. The sub-system level limits based on the statistic analysis provide plausible and rational criteria for sub-system level compliance evaluation and prevent the product from being over-designed.