Mouser Electronics White Paper

Understanding EMC Compliance

An introduction to the challenges, regulations,
and solutions for achieving EMC compliance

By Stuart Cording
 Mouser Electronics White Paper

The sheer number of electrical devices in the home these days

is tremendous. And, increasingly, these are fitted with complex
switching electronics to meet stringent efficiency requirements. For Electromagnetic Compatibility (EMC)
example, older electrical cooking hobs control the temperature using
a simple thermostat, switching the heating element on and off.
Emissions Immunity
Today, for energy efficiency, you’d select an induction hob
(Figure 1). Considering the power levels used when switching
from around 25 kHz to 100 kHz, you wouldn’t be surprised Conducted Radiated Conducted Radiated ESD EMP
if such an appliance caused issues with the operation of
touch interfaces, mobile phone operation, or caused an
audible disturbance on your radio. But it doesn’t.

Figure 2: EMC is broken down into emissions and immunity,

conducted and radiated, ESD, and EMP.

EMC regulations are defined by government bodies that

Resonant
Network
On/Off
specify the EMC standards to be fulfilled before electronic
Temp.
Control goods can be sold in their country or customs union. The
Knob
standards range from generic to specific, such as:
Heater

Hob
Bi-Metallic
Strip
Switch

• IEC 61000: Covers general considerations, definitions,

IGBT

and emissions and immunity testing guidelines.

“Simmerstat”

• IEC 61000-6-3: Generic EMC emissions standard

for residential/commercial environments.
Figure 1: Thermostat switching for an electric hob (left) and a
switching quasi-resonant circuit used in an induction hob (right). • IEC 61000-6-4: EMC emissions standard for industrial.

That’s because, since the introduction of radio communications • IEC 61851-21: Product standard for electric
in the 20th century, regulations have progressively road vehicles and charging systems.
developed to ensure our devices fulfill standards of good
interoperability in our electronics-filled world. • EN 55011/CISPR 11: Applicable to industrial,
scientific, and medical (ISM) equipment.
Electromagnetic Compatibility, or EMC, is the overarching term
used (Figure 2), but there are many potential issues behind these One of the misnomers for new developers is that EMC is a
three letters. These can be broken down into four areas: series of tests that must be passed before their product can
go to market. However, it’s a topic that should involve both
• Emissions – signals an electronic device emits through hardware and, to some extent, software developers from
radiation or conduction and is commonly described the moment the design concept starts to take shape.
as Electromagnetic Interference or EMI.

• Immunity – the ability of the electronic device to Test House Day

continue operating correctly despite subjection
to radiated or conducted emissions. While some testing can be undertaken in your laboratory, you’ll need
to take your product to an official EMC testing facility before selling
• Electrostatic Discharge (ESD) – the ability of a device to it. It makes sense to reach out to such facilities as early as possible in
continue correct operation despite subjection to ESD. the development process so they can advise which standards apply
and indicate the testing effort. Perhaps more important is finding out
• Electro-Magnetic Pulse (EMP) – a disturbance type what their availability will likely be at the later stages of your project.
of concern for defense and military equipment.
Something else that may come as a surprise is the need to
provide all operational instructions, peripherals, cables, power
supplies, and other optional equipment. For example, if your
 Mouser Electronics White Paper

device can save measurement results to a USB stick, you’ll would be a standard capability. However, it isn’t, probably
need one on test day. You should be sure that any attached due to the immense complexity of the math behind the
items are also EMC compliant, as a rogue USB drive could analysis and the processor performance required.
cause an otherwise compliant device to fail testing.
Thus, the best way forward remains to start with sound circuit layout
Your software team should also be involved in EMC because they design principles . It’s best to use approaches that deliver good power
may need to add extra software features to support testing. For and signal integrity, as these also minimise the issues that lead to
example, some modes of operation may only occur under certain troublesome radiated emissions. For example, use zoning to partition
operational conditions. Dedicated software can cycle through your design into functional blocks (supply, power, RF, analog, and
these without having to follow complex setup procedures. digital) and route high-frequency clocks close to the ground. Stubs
can also be problematic, such as short traces used as test points with
You may also need to pack some warm clothes for test no current path, as these may act as small antennas . Within a team
day, especially for emissions testing. Some facilities use an or organisation, it’s worth building up a library of “EMC Learnings,”
Open Area Test Site (OATS), an area of land free of reflective recording issues that arise and successful mitigation techniques.
structures with a ground plane between the Equipment Under
Test (EUT) and the antenna (Figure 3). This is a setup that Coupling between signals on the board can also be the source
you may be able to replicate to some degree yourself. of problems later on. A switching data line running parallel to a
trace that links to the outside world via a connector may result
in emissions issues when the external cable is attached (Figure
4). Such problems can be caught in an internal design review but
Equipment
Under Test
may be challenging to spot as complexity and board size grows.
(EUT) Antenna

R√3
MCU Tx Signal

2R
R = Typically 3 m to 10 m High-Speed

Connector
Data Signal
Memory

Transceiver
Figure 3: Setup of an Open Area Test Site (OATS) with typical dimensions.

If weatherproofing is available at the OATS location, it is constructed

of RF transparent material. Such sites are selected for low ambient
noise and any continuous emissions measured should be limited Figure 4: A high-speed signal running parallel to a trace linked to the outside
to identifiable frequencies (e.g., radio or television transmissions). world (here, via a connector) could result in radiated emission issues.
Emissions measurements are made at a distance of between 1
m and 30 m as defined in the application-relevant standard.
Circuit and Software Approaches to
Alternatively, testing may take place in an Absorber-Lined
Shielded Enclosure (ALSE) or Semi-Anechoic Chamber (SAC). Minimize Electromagnetic Radiation
These have the advantage of blocking external emissions
that interfere with measurements and avoiding poor weather Simple resistor-capacitor (RC) filters can limit the bandwidth
but are more costly to build. Testing methods and procedures of a signal at its point of origin before it is routed. Ferrite beads
for radiated emissions are provided in CISPR 16-2-3 . are another option, effectively reducing the trace length that
would otherwise act as an antenna. In switched power converter
applications, filters can be inserted between a controller’s
Designing PCBs to Pass output pin and a MOSFET device to control the rise time. It
should be noted, however, that this may only reduce the peaks
Radiated Emissions of harmonic output and not that of the fundamental frequency .
Furthermore, such a change impacts system performance,
With the wealth of online design tools available today, you’d such as reducing the power converter’s efficiency.
think that radiated emission simulation to help designers
 Mouser Electronics White Paper

Before the After the

Alternatively, microcontrollers (MCUs) or switch-mode regulator DLP11TB filter DLP11TB filter
is inserted is inserted
devices may offer spread spectrum frequency modulation
(SSFM). By increasing and decreasing a switching signal
around its fundamental, the energy in the frequency domain is
spread, resulting in a drop in the harmonic peaks. This can be
implemented using a modulation signal, such as a triangular wave, No problems in
waveforms
but pseudo-random modulation is more effective at flattening
the peak. Enabling this feature may require a pin setting or, in the Figure 6: Common mode chokes, such as the DLP Series from Murata (left),
case of an MCU, software configuration of a control register. offer good attenuation without impacting the differential signal (right).

Perhaps surprisingly, an MCU’s general purpose input/ Earlier versions of USB aren’t devoid of their challenges either.
output (GPIO) pin can also cause issues if not used in USB 2.0 uses a signalling rate of 480 Mbit/s, a frequency in
the design. GPIO should be configured as inputs and the extremities of many engineers’ design experience. Würth
connected to the ground via as short a path as possible. Elektronik provides the WE-EPLE USB 2.0 Jack with an integrated
EMC Filter , which avoids designing the filter and handling the
surface mount components yourself (Figure 7). A filter and ESD
Specifics: The Challenges of USB protection are integrated into the USB A jack housing, providing
a simple USB 2.0-tested and approved EMC solution.
For some, USB 3.0 has been an exasperating addition to
products like laptops and routers. Users reported issues using
their wireless peripherals or Wi-Fi when a USB 3 hard drive was
also operating . With its 5 Gbit/s signalling rate, the spectrum
of a data transfer looks like a sinc function (Figure 5), resulting
in significant noise at the 2.4 GHz frequency of operation
for Bluetooth, Wi-Fi, and other ISM band devices. Mitigation
approaches include better shielding for USB peripherals, improved
USB Jack Filter USB Jack with integrated filter
connector shielding within the device, and optimising placement
of radio transceivers in relation to USB 3 functionality.
Figure 7: The WE-EPLE from Würth Elektronik integrates tested
and approved EMI and ESD protection into a USB type A jack.
ISM Band

1
Exploring Emission
|A|
Sources in Your Lab
Exploring potential EMC radiation issues yourself is possible before
testing at an external laboratory. A spectrum analyser is required
0 but before selecting one, it’s worth checking that it supports the
2.5 GHZ 5 GHZ 7.5 GHZ input filter configuration defined in CISPR 16-1. Usually, the input
resolution bandwidth (RBW) is defined by a Gaussian filter with a
roll-off of 3 dB per decade. However, EMI measurements require a
Figure 5: ISM band laid over the data signal spectrum narrower filter roll-off of 6 dB per decade with 200 Hz, 9 kHz, 120
of USB 3.0 “SuperSpeed USB.” kHz, and 1 MHz bandwidths. You’ll also need a quasi-peak setting.
This weights the signal according to its repetition rate, unlike
Common mode chokes help suppress interference from parasitic averaging, which delivers the amplitude based on its period.
coupling around USB, HDMI, IEEE 1394, and LVDS circuitry.
Devices such as the DLP SMD Common Mode Chokes from Teledyne LeCroy’s T3SA3200 Spectrum Analyzer provides
Murata and Coilcraft 0603 USB 3.0 Common Mode Chokes a 9 kHz to 3.2 GHz range and can be upgraded with an EMI
are designed to offer good attenuation to unwanted signals option for the necessary filters and quasi-peak setting (Figure
without impacting the wanted differential signal (Figure 6). 8). Since an in-house test setup will have inaccuracies, ensuring
a margin of around 6 dB to the test limits is advised.
 Mouser Electronics White Paper

Summary
EMC is something that needs to be considered from day one of
designing your product. Many corrective actions for radiated
emissions require changes to the PCB design and the addition
of components, which can even have knock-on effects on the
mechanical design, such as the housing, connector placement,
or even heatsinks. With the growth in high-speed wired and
Figure 8: A spectrum analyser for radiated EMI measurements should high-frequency wireless connectivity in even the most basic
include a 6 dB roll-off filter setting and quasi-peak measurement. of applications, it’s worth building up EMC competency in-
house, investing in training and test equipment, and compiling a
If issues are found, exploring where they emanate from is eased database of issues and their resolution for use in future projects.
with near-field probes such as the T3SA3000-NFP . These can
be attached directly to the Spectrum Analyzer via its internal
preamplifier or an external wideband amplifier. Such probes
provide comparative measurements of magnetic fields ranging
from 30 MHz to 3 GHz (Figure 9). The larger circular probe
helps explore magnetic fields at a distance of up to 10 cm, while
the smaller probe suits localised measurements at up to 3
cm. Tipped probes, designed for analysis of cables, wires, and
PCB traces, are also included. The kit includes an SMB to SMA
cable and an SMA to N-type adapter. If you pair the probes with
your oscilloscope, an SMA to BNC adapter will be required.

Figure 9: Near-field probes provide comparative

measurements of PCB traces and components.

1
https://incompliancemag.com/article/basic-parameters-of-the-normalized-site-attenuation-nsa-method-for-open-area-test-sites-oats-and-
semi-anechoic-chambers-sac-in-cispr-16%E2%80%911%E2%80%914/
2
https://interferencetechnology.com/emc-radiated-emission-measurements-1351030-meters/
3
https://webstore.iec.ch/publication/653574
4
https://emcfastpass.com/wp-content/uploads/2017/04/Intel_guidelines.pdf
5
https://emcfastpass.com/rightfirsttime/
6
https://www.ti.com/seclit/ml/slup269/slup269.pdf
7
https://uk.pcmag.com/networking/13179/wireless-witch-the-truth-about-usb-30-and-wi-fi-interference
8
https://www.usb.org/sites/default/files/327216.pdf
9
https://eu.mouser.com/new/murata/muratadlp/
10
https://eu.mouser.com/new/coilcraft/coilcraft-0603-choke/
11
https://eu.mouser.com/new/wurth-elektronik/wurth-we-eple-usb-jack/
12
https://eu.mouser.com/new/teledyne-lecroy/teledyne-lecroy-t3sa-spectrum-analyzers/
13
https://eu.mouser.com/ProductDetail/Teledyne-LeCroy/T3SA3000-NFP?qs=%252BEew9%252B0nqrCaN1hwZ%2F8avg%3D%3D
14
https://eu.mouser.com/ProductDetail/Molex/73386-0031?qs=KpdAywxU013bD2%252Bk0%2F3fIQ%3D%3D