An ESD event generates significant amounts of RF radiated energy between 5 and 200 MHz. This energy often peaks at the quarterwave resonant frequency of the person performing the test. Most human bodies self-resonate at between 35 and 45 MHz. Therefore, the peak radiated emissions from ESD also peak in this same frequency range. The typical induced pulse duration times are around 400 nanoseconds.
EFTs also generate considerable radiated emissions that couple to cables and case circuitry.
The power supply EMC power-line filter provides the main protection to these transients. The CM line ground capacitors are normally the main devices used to shunt the transient currents to chassis and away from the internal circuitry. When this capacitance is limited by leakage current limits, the CM choke must provide more protection. This usually demands a special center tap CM choke, where the center tap is shunted to chassis via a capacitor that complies with the leakage current limits. It is important to use full ground and power planes, even for analog circuits, to limit high-frequency CM loops.