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OCTOBER 2025 I DESIGN007 MAGAZINE 55 distribution network. Both the PI area and thickness will determine the planar capacitors' values. Because the planar capacitance is proportional to the dielec- tric thickness between the power and ground planes, thin dielectrics are used to increase planar capaci- tance while reducing planar spreading inductance. The reduction of planar spreading inductance also results in lowering the impedance path while increas- ing the effectiveness of discrete capacitances. Divided Planar Capacitors Grouping components with a localized ground and power plane helps control EMI because the power and ground planes' geometry is sized and placed. It is not uncommon to require more than a single oper- ating voltage. The segmentation of ground planes associated with specific voltage supply functions and grouping components with a localized ground and power plane helps control EMI because the power and ground plane's geometry is sized and placed. Reasons for dividing ground and power planes: D ES I G N E RS N OT E B O O K • Separating high and low voltage areas (group devices by voltage required) • Dividing analog devices from digital devices • Preventing high-frequency effect on low- frequency circuits • Segregating one logic family from another The designer will develop the power and ground planes for each group so that the planes are the same shape and directly in line with each other, as shown in Figure 3. Avoid routing signal conductors in the narrow gap separating the power or ground planes A and B. When planning the circuit board design, remem- ber that the major role of power and ground planes is to ensure power is being uniformly distributed to all components on the circuit board's surface. Instead of routing individual power conductors everywhere, a power plane acts like a solid, wide path that supplies voltage smoothly and consistently, avoiding voltage differentials between widely distributed components. The ground plane keeps signals clean while provid- ing a low-impedance return path for current, essential in high-speed designs. When return currents can flow directly beneath their signal conductors, it minimizes signal distortion and helps improve timing. Note: Portions of the text, illustrations, and tables included in this column are from my new book, Design Guidelines for Surface Mount & Microelec- tronic Technology. DESIGN007 Vern Solberg is an independent technical consultant, specializing in SMT and microelectronics design and manufacturing technology. To read past columns, click here. F i g u re 3 : D i v i d e d p l a n a r c a p a c i to rs . ▼