In this tutorial we are going to learn about WHAT IS EMI & EMC IN PCB DESIGN

EMI: It is the process which gives out disruptive EM waves, transmits energy from one electronic device to another via radiated/conducted paths. In common usage, the term refers to RF signals. EMI Generally which have the frequency range commonly identified as “anything greater than DC to daylight.”
EMC: The capability of electrical/electronic systems/equipment & devices to operate in their intended
EM environment within a defined margin of safety & at design levels/performance, without suffering or causing unacceptable degradation as a result of EMI. Any source of changing voltage anywhere in the circuit will generate emissions. The greater the voltage or current amplitude within the circuit, the greater the source of emissions. The faster that a voltage changes level, the greater the potential interference. Sources of changing voltages (e.g all signal lines, clk, AC PWR lines) should change at the minimum rate that allows correct operation. These will always be present to some extent, but need limiting so that they avoid interfering with other equipment & comply with any legislative standards that may be applicable. Emissions can be classified as being broad band (blocks out a complete range of frequencies) or narrow band (blocks out selected frequencies, not others). Examples of broadband sources are un suppressed motors, relay contacts, car ignitions. The most common examples of narrow band sources are microprocessor clocks. Relays & other EM devices that use make & break contacts generate broad band noise. This can be absorbed by the addition of suppression components, such as capacitors, varistors, directly across the source. The conductors on the circuit that are not grounded will be acting as antennae, radiating RF energy. By keeping these conductors short & running them close to grounded, they become less efficient & will emit less. Power tracks must be wide (making them low impedance at HFs) in this way, they will be less likely to re-radiate interference themselves. If separate power tracks are used on different layers of a pcb, ensure that they are connected together at frequent intervals. Decoupling noise that does get onto the PWR lines by capacitors between PWR & GND is a good idea.

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