PCB-Level EMC, part III
Switch-mode-circuits & signallines
A measurement method for the verification of new, and the analaysis of existing Power-Distribution-Networks is presented. Pitfalls which frequently lead to erroneous ripple-measurements are uncovered. Common impedance coupling is the root cause not only of many functional issues, but also of conducted and radiated emissions. Together with field coupling it is the predominant cause of X-Talk, a key factor for a successful design! The complex nature of X-Talk is detailed, including frequency-response, rules-of-thumb and appropriate measures.
Signal characteristics and their impact on EMC are explained, possible improvements of signals and signal-paths presented. A brief introduction to differential pairs helps to counter popular misunderstandings. A number of recommendations regarding layout, stackup and circuit is derived by examining the various noise sources and coupling mechanisms imminent in switch-mode circuits. Examining ESD- and Burst-phenomena, the important steps towards good immunity are presented. The understanding of frequent connector design-flaws helps with the reduction of radiated emissions.