Imbalance Component and EM Radiation from Differential-Paired Lines with Serpentine Equi-Distance Routing

To provide the basic considerations for establishment of predicting the EM radiation from practical differential-paired lines, this paper attempts to quantify the correlation between imbalance components and EM radiation from asymmetrical differential-paired line with different serpentine equidistance routing. The differential-paired lines with different layouts were prepared for the discussion as typical different and equi-distance routing. a) is a typical asymmetrical topology due to differences in bend and length, b) is symmetrical topology with equi-distance routing, and c) is asymmetrical topology with different bend routing region. Although the geometric length of each line is the same in the symmetrical equi-distance topology, the imbalance component cannot be suppressed completely. The dominant factor of generation of imbalance component of the model under study is difference of the far-end cross-talk due to the asymmetrical geometry. The compensation region with U-shape is not effective in suppressing the imbalance component. Although serpentine equi-distance routing is suitable for improvement of SI issues compared with typical layout, it is not effective in suppressing the EMI. The reason is due to the differential-paired lines routed close to the edge of the PCB. This is significant problem of design of a meander delay line for high-speed clock distribution to establish both SI and EMI performance. This study has successfully reported the basic characteristics of imbalance component of differential-paired lines with equi-distance routing and demonstrates the dominant factor of imbalance component.