Locally shielded differential-paired lines with bend discontinuities for SI and EMI performances

To provide the basic considerations for EM radiation from practical asymmetrical differential-paired lines with bend routing, this paper newly attempts to propose locally shielded differential-paired lines for establishing SI performance and suppressing imbalance component and EMI generated by differential-paired lines with bend (turnoff point) discontinuities. The conductive plane is placed on discontinuity region asymmetrically. The concept of locally shielded layout is based on compensation of phase-difference due to the bend discontinuities, by using electric-coupling between signal trace and a conductive plane for the shield. The proposed method is suitable for implementing on PCB, without changing layout of the differential-paired lines. To compare the effect of the locally shielded paired-lines on CM component, the S_cd21, which is defined as the conversion from DM to CM, are evaluated. The significant suppression effectiveness of S_cd21 in the case study is achieved below 1 GHz by locally shielded differential-paired lines. Consequently, the validity of the proposed locally shielded layout is demonstrated in the case study. It is demonstrated that the proposed locally shielded layout is suitable for improving the SI performance and suppressing the CM in the case study. This study has successfully reported the basic method for suppressing imbalance component of differential-paired lines with bend discontinuities.