Weak-Coupled Cross-Sectional Differential-Paired Lines with Bend Discontinuities for SI and EMI Performances

For differential-signaling system, the ideal balance or symmetrical topology cannot be established due to bend (turnoff point) discontinuities, and hence, an imbalance component is excited. Therefore methodology and geometrical-structure for satisfying both SI and EMI performances are indispensable. In order to provide basic considerations for the realization of methods for predicting and suppressing the EM radiation from asymmetrical differential-paired lines, the imbalance component and EMI from strong and weak coupled differential-paired lines with bend discontinuities were studied experimentally and with modeling. Firstly differential-mode impedance and the mixed-mode scattering parameters are discussed, from view point of SI performance. Secondly, frequency response of electric field near a PCB are discussed, from view point of EMI. It is demonstrated that the differential-paired line with weak-coupling is suitable for improving the SI performance and suppressing the EMI. This study has successfully reported the basic characteristics of imbalance component of differential-paired lines with bend routing and demonstrates the dominant factor of imbalance component.