• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

Analog IC Tips

Analog IC Design, Products, Tools Layout

  • Products
    • Amplifiers
    • Clocks & Timing
    • Data Converters
    • EMI/RFI
    • Interface & Isolation
    • MEMS & Sensors
  • Applications
    • Audio
    • Automotive/Transportation
    • Industrial
    • IoT
    • Medical
    • Telecommunications
    • Wireless
  • Learn
    • eBooks / Tech Tips
    • FAQs
    • EE Learning Center
    • EE Training Days
    • Tech Toolboxes
    • Webinars & Digital Events
  • Resources
    • Design Guide Library
    • Digital Issues
    • Engineering Diversity & Inclusion
    • LEAP Awards
    • Podcasts
    • White Papers
    • DesignFast
  • Video
    • EE Videos
    • Teardown Videos
  • EE Forums
    • EDABoard.com
    • Electro-Tech-Online.com
  • Engineering Training Days
  • Advertise
  • Subscribe

Conducted and coupled EMI/EMC concepts

June 26, 2020 By Jeff Shepard

In addition to the International Telecommunications Union (discussed in part 1 of this FAQ series), there are several organizations that define and regulate acceptable levels of conducted and radiated emissions from electronic devices. These various agencies have developed numerous standards generally based on the operational environment of the specific device. Effectively managing EMI is a complex task. This FAQ provides an overview of some considerations for managing conducted and coupled emissions.

The table below provides a summary of several areas covered by specific conducted emissions standards. In addition to these commercial, industrial, and consumer standards, there are a variety of military and aerospace standards for emissions. One of the most commonly-specified are the MIL-STD-461 test procedures that define the test levels and test limits of electronic equipment used by the US military. MIL-STD-461 covers a wide variety of conducted emissions and susceptibility tests as well as a number of radiated emissions and susceptibility tests.

Summary of main non-military standards for conducted emissions (Image: Texas Instruments)

Many systems, especially switch-mode power converters, employ filters to control conducted emissions. While effective, these filters add to system size and cost. They can be either internal to the design or added externally. Even if individual power converters or other sub-systems include internal EMI filters, the addition of an external filter may be needed in systems with multiple power converters or other EMI sources such as high-speed microprocessors. EMI is additive and the sum of the individual sources can easily sum to more than can be filtered by the already included filter(s). In other cases, a filter may need to be added to a system designed to meet less stringent EMI limits, but that is being used in a more noise-sensitive environment. Standard external filters can be single-stage or multi-stage and are offered in single-phase or three-phase designs.

Examples of external EMI single-phase filters (Image: TE Connectivity)

Differential-mode and common-mode EMI

As illustrated below, conducted EMI can take the form of differential- or common-mode energy. Differential-mode noise can sometimes be referred to as “normal-mode” noise. Common-mode noise is created by leakage, usually through a stray impedance, such as capacitance or inductance, and is a form of coupled emissions.

Both differential- and common-mode noise can produce radiated EMI. In a typical design, common-mode noise produces much more radiated emissions than differential-mode noise. In fact, common-mode noise can produce as much as two orders of magnitude more radiated emissions than a similar level of differential-mode noise. That makes it particularly important to address common-mode noise to prevent excessive radiated emissions.

EMI/EMC Concepts
Differential- and common-mode noise characteristics (Image: ROHM)

As an example, common-mode noise can be suppressed using bypass capacitors connected between the power supply lines and ground. Bypass capacitors for the suppression of common-mode noise can be connected at both the input and/or the output. Common-mode noise can be further reduced by adding a pair of coupled-choke inductors in series with each power line. The coupled-choke inductors present a high-impedance path to the common-mode noise currents, forcing the currents to flow through the bypass capacitors and into ground.

Good EMC design is usually a two-way street. A design that emits unnecessarily large amounts of EMI (whether conducted to radiated) is also usually more susceptible to external EMI sources. So, reducing emissions also often results in lower electromagnetic susceptibility and improved system performance.

Testing for conducted EMI

Basic conducted emissions testing setup (Image: CUI, Inc.)

While good design practices are required to control EMI, testing is also essential. Early testing can accelerate the certification process that is required before taking products to market. In-house testing does not generally replace certification by an independent testing laboratory. But in-house testing during product development can provide early identification of potential trouble areas and shorten time to market. Testing conducted emissions is relatively straight-forward. It requires a line impedance stabilization network (LISN), spectrum analyzer, and appropriately insulated/isolated testing set-up. Your spectrum analyzer supplier can usually provide specific instructions for implementing an effective conducted emissions test procedure.

References

An overview of conducted EMI specifications for power supplies, Texas Instruments
(Normal) Mode Noise and Common Mode Noise – Causes and Measures, ROHM
List of common EMC test standards, Wikipedia
The Importance of EMC Testing Early in Your Product’s Design, CUI, Inc.

 

You may also like:


  • A comparison of EMI test setups and specifications for automotive,…

  • A comparison of EMI test setups and specifications for automotive,…
  • op amp variations
    Electrical noise can come from anywhere
  • EMI
    EMI, EMC, EMS, and the ITU

Filed Under: EMI/RFI, FAQ, Featured, Products Tagged With: FAQ

Primary Sidebar

Featured Contributions

Design a circuit for ultra-low power sensor applications

Active baluns bridge the microwave and digital worlds

Managing design complexity and global collaboration with IP-centric design

PCB design best practices for ECAD/MCAD collaboration

Open RAN networks pass the time

More Featured Contributions

EE TECH TOOLBOX

“ee
Tech Toolbox: 5G Technology
This Tech Toolbox covers the basics of 5G technology plus a story about how engineers designed and built a prototype DSL router mostly from old cellphone parts. Download this first 5G/wired/wireless communications Tech Toolbox to learn more!

EE LEARNING CENTER

EE Learning Center
“analog
EXPAND YOUR KNOWLEDGE AND STAY CONNECTED
Get the latest info on technologies, tools and strategies for EE professionals.

EE ENGINEERING TRAINING DAYS

engineering

RSS Current EDABoard.com discussions

  • Diode recovery test Irrm timing.
  • Battery Deep Discharge – IC Workarounds?
  • The Analog Gods Hate Me
  • Safe Current and Power Density Limits in PCB Copper(in A/m² and W/m³) simulation
  • Why so few Phase shift full bridge controllers?

RSS Current Electro-Tech-Online.com Discussions

  • Wideband matching an electrically short bowtie antenna; 50 ohm, 434 MHz
  • The Analog Gods Hate Me
  • Simple LED Analog Clock Idea
  • PIC KIT 3 not able to program dsPIC
  • Parts required for a personal project
“bills

Design Fast

Component Selection Made Simple.

Try it Today
design fast globle

Footer

Analog IC Tips

EE WORLD ONLINE NETWORK

  • 5G Technology World
  • EE World Online
  • Engineers Garage
  • Battery Power Tips
  • Connector Tips
  • DesignFast
  • EDA Board Forums
  • Electro Tech Online Forums
  • EV Engineering
  • Microcontroller Tips
  • Power Electronic Tips
  • Sensor Tips
  • Test and Measurement Tips

ANALOG IC TIPS

  • Subscribe to our newsletter
  • Advertise with us
  • Contact us
  • About us

Copyright © 2025 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy