A method for compensating imbalance component of asymmetrical differential-paired lines due to turnoff point for SI and EMI performances

For differential-signaling system, the ideal balance or symmetrical topology cannot be established due to discontinuities at turnoff point (90-degree turn), so called bending, 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 compensating the imbalance component and suppressing the EM radiation from asymmetrical differential-paired lines, the imbalance component and EMI from the differential-paired lines with discontinuities at turnoff point were studied experimentally and with numerical modeling. The differential-paired lines with different layouts were prepared for the discussion as typical routing. In the method, the distance between the paired lines at turnoff point is narrow, and hence the difference of length between Line 1 and 2 is compensated. Therefore the suppression of imbalance component by compensating the difference of the length and suppression of EMI by narrower separation can be achieved. Firstly the mixed-mode scattering parameters are discussed, from view point of SI performance. Secondly, frequency responses of electric-field and magnetic-field near a PCB are discussed, from view point of EMI. It is demonstrated that the proposed method 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 turnoff point.