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48 DESIGN007 MAGAZINE I FEBRUARY 2024 Embedding components into the multilayer PCB substrate can have many benefits, includ- ing reduced board size and improved signal integrity. However, embedded capacitance material (which is not really a component but rather part of the substrate) can improve power integrity dramatically by reducing AC impedance and generally enhancing the per- formance of the product. It takes up no addi- tional space, is easy to implement (because it is compatible with standard FR-4 processes), and can be cost-effective. A combination of components is generally required to optimize the power distribution Embedded Capacitance Material network (PDN). Figure 1 shows how each component has a specific resonant frequency at which point the impedance will be low. e voltage regulator module (VRM), bulk bypass and decoupling capacitors, plane, die capaci- tance plus BGA via, and via spreading induc- tance all influence the PDN at different fre- quencies. e goal is to keep the AC impedance low over the entire signal bandwidth. How- ever, decoupling capacitors are only effective up to a few hundred megahertz. Above that, only on-die capacitors or planar capacitance can reduce the impedance significantly due to their low inductance. Beyond Design Feature Column by Barry Olney, IN-CIRCUIT DESIGN PTY LTD / AUSTRALIA Figure 1: Target impedance, VRM, capacitor, and plane profiles of a PDN.

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