Dominant factors of electromagnetic interference problems of asymmetrical and equi-distance differential-paired lines

Multichannel differential signaling scheme is one of the key technologies for modern electronics systems. For actual system, the ideal balance or symmetrical topology cannot be established, and hence, an imbalance component is excited. To provide the basic considerations for electromagnetic (EM) radiation from practical asymmetrical differential-paired lines structure with equi-distance routing, in which the same-length paired lines are used in high-speed board/LSI layout design, in this paper we newly attempt to clarify the characteristics and to identify dominant imbalance and EM radiation factor from asymmetrical differential-paired lines, by a physics-based model. The frequency response of EM radiation from asymmetrical differential-paired lines can be identified using the physics-based model. The physics-based model is constructed with an equivalent circuit model to calculate current distribution, and radiation model based on Hertzian dipole antenna. It is validated by comparing the predicted results with finite difference time domain simulation. This paper reported the basic characteristics of imbalance component of differential-paired lines with asymmetrical equi-distance routing and demonstrates the dominant factor of imbalance component and EM radiation successfully.