Analysis and control of electromagnetic emission for ringing signal

Ringing signal has widely existed in digital circuits like integrated circuits, DC-DC circuits, etc. The ringing appears in the roads due to the parasitic effect in high frequency or the impedance mismatch, and may cause logical errors in signal processing, as well as electromagnetic interference (EMI) to other devices. To have a deeper understanding of the electromagnetic characteristics, we analyze the generic causes of ringing, and formulate its mathematic time-domain expression. Based on the time-domain formulations, a study of spectrum characteristics for ringing is made with the aid of Fourier transform, trying to find out ring's electromagnetic features. We also study the square wave signal's properties in time-frequency domain. Comparisons between ringing and square wave have been made, in order to support the electromagnetic compatibility (EMC) design of circuits.