Time‐domain ringing noise analysis induced in transmission lines using the common and normal mode concepts

Summary In circuit design, it is important to understand the effect of circuit structure on the generation of electromagnetic noise. Analyses of ringing noise induced in three transmission lines connected to lumped‐parameter electronics are presented experimentally and theoretically. Four types of circuits classified with structures of lumped‐ and distributed‐parameter circuits are investigated. Symmetrical relations of three line positions and lumped‐parameter electronics suppress ringing noise, whereas asymmetry of either of the distributed‐ and lumped‐parameter circuits induces ringing noise, even the impedance matching condition is imposed in the normal mode. We analytically elucidate the origin of various behaviors of ringing noise caused by the circuit structures using the concept of the normal and common modes. In this paper, we investigate common‐mode (CM) noise caused by asymmetry of circuit configurations. We use three conductor transmission lines where two lines express circuit and the third line expresses environment of circuit to introduce normal‐mode (NM) and CM concept. CM ringing noise generates when a circuit has asymmetry configuration between lumped‐parameter circuits and transmission lines at the end of the circuit. We analysis CM ringing noise experimentally and theoretically to understand ringing noise phenomena in time domain. We show the mechanism of CM noise generation by analyzing the transient response of NM and CM. Furthermore, we express the CM noise ringing behavior by introducing attenuation matrix and elucidate the relationship between circuit configurations and CM noise ringing behaviors.