Using Electric and Magnetic “Moments” to Characterize IC Coupling to Cables and Enclosures

The electric field coupling from ICs to cables or enclosures is proportional to the source voltage, source frequency and the self capacitance of the IC structure. The product of these three values is a quantity that effectively represents the strength of an electric field source independent of the structure(s) that it may couple to. Magnetic field coupling from the small circulating currents generated by ICs and their packages is proportional to the source current, source frequency and the effective mutual inductance associated with the coupling path. The product of these quantities is also a scalar value and represents an IC’s ability to couple to cables and enclosures through a magnetic field. These electric and magnetic “moments” can be used to characterize an IC’s ability to couple noise to its external environment. These moments depend on local geometric parameters such as the circuit board dimensions, IC package structure, presence of heatsinks, etc., but they are independent of system parameters such as cable and enclosure geometries. Measurements of ICs in a TEM cell with a hybrid can be used to determine these electric and magnetic moments. These moments can then be used to estimate the maximum radiated emissions from the ICs in a given environment. Vin