When trying to minimise the impact of electromagnetic interference (EMI), the layout of the Printed Circuit Board (PCB) is of critical importance. Yet, ironically, when designing for EMI, PCB layout is often one of the least understood factors.
However, actually taking EMI into consideration need not be particularly complicated. Observing a few key points can make the process extremely effective. When designing for EMI, it is of paramount importance to minimise link areas, leave no floating parts, ensure all loops are brought back to ground, and to ensure that signal and power ground connections are kept separate.
Incorporating these design features will unquestionably add to the complexity of the PCB design, thus it is normal practice to compromise to some extent in order to save on layers.
Another issue which power supply designers have to address is that the end of a performance is not typically characterised by the manufacturer of a component. Therefore it is often something that needs to be assessed by designers themselves. Thus, understanding components becomes a critical element in deciphering how they will behave in emission terms. Additionally, elements of a device such as capacitors, wire wound resistors and wire leads can vary in behaviour when frequency changes within a power supply.
As well as minimising radiation sources, it is also important for designers to ensure that the system is optimally arranged with regard to performance. The biggest contributors to EMC performance are cabling arrangements and PCB tracking layouts. Thus, it is of critical importance that PCB tracks and power cables are arranged to minimise current carrying loops, and additionally to minimise any loops which could have noise currents induced within them. A good role of thumb is that all cables and PC tracks should be viewed as potential radiation sources, and every attempt should be implemented to minimise any interaction between them.
By following these basic guidelines related to PCB, the likelihood of minimising electromagnetic interference is greatly increased.