Reduction of Common Mode (CM) and Differential Mode (DM) radiated emission

 Differential Mode Radiation can be reduced by

1) Reducing the magnitude of the current
2) Reducing the frequency of harmonic content of the current
3) Reducing the loop area

Common Mode Radiation can be reduced by

1) Minimising the source voltage that drives the antenna (normally ground potential)
2) Providing a large common mode impedance in series with the cable or printed track
3) Shunting the current to ground
4) Shielding

Reduction of Common Mode (CM) and Differential Mode (DM) radiated emission

To reduce the radiated emission, we must;
1) Reduce the frequency of the signal, ie, the rise and fall time, if possible
2) Reduce the loop area – eliminate or reduce all loop area by reducing the ground loop, the signal loop by decoupling
3) Reduce the inductance of the ground plane, mutual inductance of signal and return paths. By minimising the loop area where the signal flows, we have to reduce the mutual inductance in that circuit.
4) Eliminate or reduce all radiating antenna
5) Reduce or eliminate the noise source, differential voltage, if possible. Etc.

Methods of reducing of susceptibility to radiation

1) Balance the circuit, if possible
2) Reduce all loops that can pick up the radiation by induction current flow
3) Increase/decrease the impedance of the circuit to pick up depending on whether it is near field magnetic or electric field induction.
4) Reduce or eliminate all pick up antennas
5) Apply shield and crosstalk reduction technique, etc.

EMC Consideration

Overview Of EMC

Electromagnetic interference is a serious and increasing form of environmental pollution. The large number of electronic devices in common use is partly responsible for this trend. Adopting the practices of electromagnetic compatibility (EMC) controls the pollution level of electromagnetic interference.

Definitions

•  Electromagnetic Compatibility (EMC):

Ability of a product, equipment, system to operate satisfactorily in, and not overly contribute to, an electromagnetic environment.

•Electromagnetic Interference (EMI):

Electromagnetic energy emanating from one device which causes another device to have degraded performance.

•Electromagnetic Susceptibility (Immunity) (EMS):

Ability to function properly in its intended electromagnetic environment. Tolerance in the presence of electromagnetic energy.

Simply put, EMC is to design equipment that  neither generates, nor is susceptible to, interference.

The performance level and requirement of Electromagnetic Compatibility (EMC) for any electronic product or system are specified by EMC regulations. These specified levels are enforced by individual country’s EMC regulations and standards. Failing to comply with these requirements can result in forced removal of a product from the marketplace, confiscation of non-compliant product, monetary fines, and in extreme cases, imprisonment.

Countries adopt different EMC Standards. Most adopt CISPR (International Special Committee for Radio Interference) as their national EMC regulation. In the US, the body responsible for EMC is FCC (Federal Communications Commission). For military applications, the EMC standard is MIL-STD-461E. These EMC Standards specifies what facilities to be used and how measurement are to be carried out.