PCB design techniques for lowest-costI EMC compliance: Part2

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PCB design techniques for lowest-costI EMC compliance: Part2

by M. K. ARMstrong
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& t& W6 w$ L% n4 [5 P# n4 J4 DPrinted circuit boards (PCBs) are widely used in electronic equipment and systems.Application of good EMC (electromagnetic compatibility) practices to their design usually helps to achieve compliance with EMC regulations at much lower cost than alternative EMC measures at higher levels of integration, and also improves signal integrity. This, the second part of the paper discusses in detail techniques for improving the power supply of a PCB and using transmission lines.
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/ M. k# `3 \' k! z' G) G8 A1 Introduction
5 _/ b+ ?* a  @& q) o& V% lPart 1 of this paper discussed how the techniques of circuit segregation, inteRFace suppression and the use of ground and power planes can be applied to printed circuit boards (PCBs) to help improve the EMC (electromagnetic compatibllity) performance of electronic equipment and systems. Part 2 discusses two further techniques: power
/ }$ r5 M* R" `7 z' L; [" u' H% @decoupling and the use of transmission lines. These five best-practice' EMC techniques interact with each other to give dramatic improvements in the EMC of electronic
circuits which use PCBs.
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2 Power decoupling
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- j% Y7 n6 `4 l4 w( GThis technique must be considered as a part of the circuit design process itself, as well as part of the PCB layout. The aim of power decoupling, crudely put, is to maintain the power supply impedance to each IC on the PCB to 1 9 or less across the entire frequency range of interest for EMC (at least 150 kHz to 1 GHz). Some high-speed or powerful ICs may require a power supply impedance of0-1 Q or less over certain frequency ranges for correct operation. Wires and PCB tracks all have much too much inductance to provide such low impedances.
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