Identifying EM radiation from asymmetrical differential-paired lines with equi-distance routing

Differential-signaling (DS) techniques such as low-voltage differential-signaling (LVDS) are widely used in digital electronic devices in order to establish a high-speed digital propagation with low-electromagnetic interference (EMI). For actual DS, the ideal balance or symmetrical topology cannot be established, and hence, an imbalance component is excited in practical high-density packaging systems. In this paper, we newly attempt to identify and quantify the frequency responses of the imbalance component and electromagnetic (EM) radiation when the structure and topology change from a symmetrical to an asymmetrical differential-paired lines with equi-distance routing, using a physics-based model, which is constructed with an equivalent circuit model to calculate current distribution, and radiation model based on Hertzian dipole antenna. The physics-based model is validated by comparing the predicted results with FDTD simulation. The frequency response of EM radiation from asymmetrical differential-paired lines can be identified using our proposed model. This study has successfully established a basic method to effectively predict EM radiation from practical differential-paired lines.