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Design007-Oct2022

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56 DESIGN007 MAGAZINE I OCTOBER 2022 Inductive kick has been a well-known phe- nomenon in the electronics industry from very early on. First associated with motors, AC mains transformers and mechanical relays, people noticed large voltage spikes when the current-carrying circuit was opened. Later, as more sophisticated electronic circuits emerged, the same thing was noticed any time current was changing through an inductor, or for that matter, through any inductance, whether it was an intentionally placed discrete inductor piece or just the parasitic inductance associated with a current path. is phenome- non is captured by the third Maxwell equation, which describes Faraday's Law 1 . In its simple form we know this rule from signal integrity as it describes the Dv ground bounce as a function of the dI/dt rate of change of current through an inductance of L: In today's electronics, the components are held and connected by printed circuit boards, which have been around for several decades. e front and back side of a small printed cir- cuit board I designed, etched and populated in the late 1960s, are shown in Figure 1. It was the audio amplifier for a battery- powered portable radio using all germanium transistors. e printed circuit board dielec- tric was unreinforced, fairly brittle, and to connect all components it was enough to use copper traces only on the back side of the board. e power and ground nets were car- ried by the wider etches near the two edges of the board. Being an analog audio amplifier using low-frequency transistors with a transit frequency in the order of a megahertz, the cir- cuit did not create high-frequency or high-speed noise, and to carry power around simple traces with no special high-frequency bypassing was suf- ficient. ough the L inductance of the widely-spaced power and ground traces must have been very high, Noise Mitigation in Power Planes Quiet Power by Istvan Novak, SAMTEC Figure 1: Small battery-powered audio amplifier on a single-sided printed circuit board from the late 1960s. a b

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