Effect of package parasitics on conducted and radiated emission with mixed-mode analysis

Based on a case study it is shown that the mixed-mode scattering parameters allow to consider some important effects related to package parasitics, which cannot be explained by considering completely differential type package models. In particular, a differential mode source at IC level can generate a common mode current at package level, which is in part transformed back into differential mode current and flows through the port connected to the PCB. Some design equations based on mixed-mode analysis are proposed, in order to reduce the common mode excitation, and make in this way the package more reliable.