EMC Fundamentals & PCB Layout Principles

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Electromagnetic Interference (EMI) has two forms: conducted and radiated. Conducted interference occurs when noise from an electronic device is transmitted through a conductive medium or a common power line, affecting other equipment. Radiated interference happens when an electronic device's noise signals are coupled through space to another electrical network or device.

To prevent electromagnetic interference from electronic products from affecting or disrupting the normal operation of other devices, various governments and international organizations have established regulations and standards. Products that comply with these regulations are considered to have electromagnetic compatibility (EMC).

EMC standards are not static and are subject to continuous change, often driven by the evolving policies of national governments and economic organizations.

EMC Standards and Testing

International Standards

IEC (International Electrotechnical Commission)
ISO (International Organization for Standardization)
IEEE (Institute of Electrical and Electronics Engineers)
ETSI (European Telecommunications Standards Institute)
CCIR (International Radio Consultative Committee)
ITU (International Telecommunication Union)
The IEC has the following sub-committees for EMC standards research:
- CISPR: International Special Committee on Radio Interference
- TC77: Technical Committee on Electromagnetic compatibility between equipment including networks
- TC65: Industrial-process measurement and control

National and Regional Standards

FCC (Federal Communications Commission, USA)
VDE (Verband der Elektrotechnik, Germany)
VCCI (Voluntary Control Council for Interference, Japan)
BS (British Standards)
ANSI (American National Standards Institute)
GOST-R (Russian Government Standard)
GB, GB/T (Chinese National Standards)

EMI Testing

Radiated Emissions (RE)
Disturbance Power (DP)
Conducted Emissions (CE)
Harmonic Current Emissions
Voltage Fluctuations and Flicker
Transient Disturbance Voltage (TDV)

EMS Testing

Radiated Susceptibility (RS)
Power-frequency Magnetic Field Susceptibility (PMS)
Electrostatic Discharge (ESD) Immunity
Conducted Susceptibility induced by RF fields (CS)
Voltage Dips, Short Interruptions, and Voltage Variations Immunity (DIP)
Surge Immunity
Electrical Fast Transient/Burst Immunity (EFT/B)
Power Line Induction/Contact

Evaluation of EMC Test Results

Class A: Normal performance within specified limits.
Class B: Temporary degradation of performance, which is self-recoverable after the test.
Class C: Temporary loss of function, which is self-recoverable or can be restored by operator intervention.
Class R: Non-recoverable loss of function or performance degradation due to equipment damage, software corruption, or data loss is not allowed (excluding protective components).