How to design for emc

Created: April 2020Last updated: 05/19/2020


The ultimate goal of EMC design is to ensure your product does not interfere or suffer from any noise (either radiated or conducted) with other electrical product or system in its vicinity.


Electromagnetic Compatibility of an electronic equipment is often overlooked in early stage of the product design cycle until the product fails regulatory compliance tests such as FCC and CE in later stage.  Mostly due to insufficient understand of EMC principles and underestimate the EMC compliance test time and cost.

Most commonly seen EMC failures seen in consumer electronics design are immunity and emission.

Failing a regulatory compliance certification at this stage often results in teams scrambling to find a fast band-aid solution that compromises product performance; Hence, we strongly recommend  engineers to to start EMC design early. A good EMC design is one of the main differentiating factor that  separates between a premium and consumer friendly branded products.


EMC the ability of the electronic equipment to operate under its intended usage and environment without unacceptable user experience due to electromagnetic interference.

         Note: the source of interference in the above context can be  from an external source or self-generated.

EMC Overview

EMC can be breakdown in two parts:



EMC Impacts



EMC Diagram

Understand emission and immunity

Emission is categorized as 

Immunity is categorized as

EMC Mitigation

Emission Mitigation

Common sources of emission is listed below

Immunity Mitigation

Common sources of external interference is listed below

EMC Compliance Test Overview

Most common regulatory compliance bodies are FCC [US] and CE [EU]. However, CE has more mandated test cases such as ESD, power surge, harmonic current, etc., but both regulatory bodies cover the same RE/CE and RI/CI test criteria. Often meeting CE compliance will suffice for FCC.

Radiated Emission Test

A test receiving antenna and equipment under test (EUT) are placed inside an approved EMC chamber during testing. EUT is then put in normal operation state during testing

The purpose of emission test is to determine whether or not the emission level is under required regulatory limits.

Conducted Emission Test

A line impedance stabilization network (LISN) is inserted between EUT and wall outlet to decouple noise current existing out of EUT power cord  from main AC signal and provides a decoupled noise port for measurement. 

The purpose of conducted test is determine whether or not the noise current level is under required regulatory limits.

EMC Testing Overview

Recommended EMC criteria




Example Standards:

IEC CISPR 32 : Emission product limit for multi-media equipement.

IEC 61000-6-3: Generic Emission standards for residential and commercial.

IEC 61000-6-1: Generic Immunity standards for residential and commercial.

FCC Title 47, Part 15, Subpart B ; USB FCC EMC Standards


Further Reading

"Basic Knowledge of EMC Standards",