FUNDAMENTALS OF EMC

Candace Suriano

John Suriano

Special Thanks to our Sponsor

Helpful books on EMC

Helpful books on Signals

Articles:

Candace Suriano, John Suriano, Tom Holmes. Qin Yu, “Antenna Fundamentals,” Interference

Technology May 3, 2007.

Candace Suriano, John Suriano, “Christmas Music in the Chamber,” Interference Technology, March

21, 2012.

Candace Suriano, John Suriano, “EMC War Stories: Letters from Home PART 1: MY CELL PHONE

CAN TALK TO ME IN STEREO,” Interference Technology, March 20, 2014.

Candace Suriano, John Suriano, “EMC War Stories: Letters from Home Part 2: It’s hard for my

computer to sleep when I’m doing the laundry” , Interference Technology, April 14, 2015.

Blogs:

Candace Suriano, “If You Don’t Like Modeling with a Computer, Try Using Tape and Foil,” Interference

Technology, April 27, 2018.

Candace Suriano, “Oh How I Hate to Commutate!” Interference Technology, May 18, 2018.

Candace Suriano, “The Übersystem, Automotive Ethernet: An Interview with Stephen

Jackson,” Interference Technology, September 11, 2018.

Much of our material can be found in these articles

How to have a bad day

Overview

•What is EMC and Who Cares about it?

•How Do People Measure EMC?

•Key Elements of EMC

•EMC for Everyone

Part 1: The stuff that makes EMC

What you should learn from Part 1

• What are the two sides of EMC?

• What is the difference between narrowband and broadband?

• Name 2 types of broadband noise

• Name 3 types of narrowband modulation

• How does 60 Hz switching of a light make noise at 1MHz that interferes with AM radio?

• How does a cell phone operating at GHz frequency make an audio frequency noise in a speaker?

• What is the difference between common and differential mode?

• How do we get rid of conducted problems?

• How do we get rid of radiated problems?

• What are three ways to measure or introduce electromagnetic noise?

What is EMC?

EMC is used to insure that electrical devices do

not interfere with other equipment or themselves

and are not affected by other devices.

EMC = Electromagnetic Compatibility

What are the Two Sides of EMC?

What is EMC? Side 1

Don’t Make Noise

•EMISSIONS

Reduce the noise made by

What is EMC?

Don’t Blow Up

•IMMUNITY

Preventing malfunction due to EM interference

Who Cares About EMC?

•Governments (FCC, EU,CCC)

•People on airplanes

•Automobile Manufacturers

•Anyone who gets interference on their radio

•Hospitals

•Lawyers $$$

What Causes EMC Problems?

•Wires for power or communications

•Electronic or mechanical switches

•Circuit board and IC design

•Cycle rate of software

•’70’s Shag carpet

What you need to know to work on EMC

•Electromagnetics

•Signal Processing

•Communications

•Analog Electronics

•Digital Electronics

•PCB Layout

•Software

What is involved in the study of EMC?

• Electromagnetics

• Signal Processing

• Electronics

• Communications

Source: Agilent.com

Types of EMC Tests

• Emissions• Radiated Emissions

• Conducted Emissions

• Conducted Transients

• Immunity• Radiated Immunity

• Conducted Immunity

• Electrostatic Discharge

Emissions Testing

• Conducted transient emissions-Unplugging the blender

• Conducted RF emissions-Running the blender while watching TV

• Radiated RF emissions-Running the blender while listening to Sony Walkman

™(radio)

• Magnetic Field Emissions-Placing speakers next to computer monitor

Immunity Testing

• Conducted immunity-Why you should unplug your computer during a thunder storm

• Radiated immunity-Why you shouldn’t place your iPod™ in a microwave oven

• Current injection and coupling-Why you should not run network cable next to house wiring

• ESD-Do you really have to stay outside your car while re-fueling?

Measurement FacilitiesReverberation Chamber

Source: www.ets-lindgren.com

Source: www.walmart.com

Measurement FacilitiesSemianechoic and Anechoic Chambers

Source: www.de.afrl.af.mil

Source: www.epg.army.mil

Source: www.ets-lindgren.com

EMC Equipment

•Antennas and Probes

•EMI receivers and spectrum analyzers

•Artificial Networks

•Oscilloscopes

•Transient generators

•ESD guns

•Power amplifiers

•Standards, specifications and procedures

1MHz 10MHz 100MHz 1GHz 10GHz

AM Radio FM Radio Cell Phones Mobile Radios

Time domain vs. Frequency domain

• We live in the “time domain” everything we observe starts, stops, and changes as a function of time

• Signals in the time domain can be broken up into components in the “frequency domain” showing the relative occurrence of repetitive portions of the signal

Types of signals that cause noise• Continuous

• 60 Hz power lines• Someone using a signal generator

• Modulated• All radio, TV and communications transmissions• Cell phones• Radar

• Digital

• Transient• Electrostatic discharge• Inductive switching

• Random• Thermal noise from the universe

Types of EMC Noise

•Broadband Noise

•Narrow Band NoiseFrequency

Signal

Frequency

Signal

DC Motors

Switching Circuits

Mechanical Relays

Thermal noise

Radio Stations

Communications

Microprocessor Clocks

Terminology of spectrum measurement• Resolution Bandwidth

• Video Bandwidth

• Dynamic Range

• Attenuation

• Reference Level

• Preamplifier

• Preselector

• Impulse Response

• Time Domain Scan, Fast Fourier Transform

• IEC CISPR 16

dB is for everyone (but not for everyzero)

• The use of logarithms allows us to view signal details over many orders of magnitude.

• Small differences of small signals and big differences of big signals can be observed

• dB of voltage 20*log10(V/Vref) where Vref is a reference voltage• Ex: 1V→ 20*log10(1e6uV/1mV) = 120dBmV

• dB of power 10* log10(P/Pref) • Ex: 1W →10* log10(1000mW/1mW)=30dBm

• a 20dB increase in voltage (X10) is also a 20dB increase in power (X100) because power is proportional to V2

Types of Broad Band noise•Coherent broadband noise is made up of noise spikes that simultaneously occur and are regularly spaced

• The signal strength is constant (sort of) over frequency (amplitude increases linearly with bandwidth, power increases by square of bandwidth)

• Incoherent broadband noise is made up of noise spikes that randomly occur and are not regularly spaced

• The power density is constant over frequency (amplitude increases by square root of bandwidth, power increases linearly with bandwidth)

Bandwidth is not a measure of the waist size of the percussion section

Resolution bandwidth

A

Bandwidth is the frequency width of a filter: The filter is a “funnel” which accumulates signals within the bandwidth and spits them out as a single value (i.e. it integrates the signal to give a value of the strength at a given frequency)

Bandwidth for one is not bandwidth for other

3dB

6dB

RBW

RBW

A 3dB bandwidth is used by MIL-STD

A 6dB bandwidth is used by CISPR

Modulation of Narrow Band Signals• Narrow band signal of one frequency is Continuous Wave (CW)

• Communication signals are attached to a signal of one frequency called the carrier frequency

• Sometimes the carrier frequency is continuously altered. This is known as “spread spectrum”

• Communication signals are attached by modulation• Amplitude modulation changes the amplitude of the carrier according to

the signal

• Frequency modulation changes the frequency of the carrier according to the signal

• Pulse modulation turns the carrier on and off according to a digital signal

Narrow Band Signals

Narrow Band Signal Modulation

Narrow Band Noise

Types of broadband noiseSwitching Transitions

RC Transitions

Square Wave

Fundamental

Harmonics from a signal can produce noise at higher frequencies

Chart Title

Pulse Modulation

Pulse frequencyCarrier frequency

Modulation of a signal can produce noise at lower frequencies

Note: this can be the result of software cycling

Sine (CW)

Continuous wave signal can produce noise at only one frequency

Exponential Decay

How do signals get from one device to another?

•Conduction: ESD and transients

•Capacitive Coupling

•Inductive Coupling (Transformer)

•Radiation

How to transmit noise

Magnetic coupling(loops)

Electric coupling(plates)

Radiation(wires)

The Key to EMC?

• Differential Mode Current

-Conducted Emissions and Immunity

The Key to EMC?

• Common Mode Current

-Radiated Emissions and Immunity

Common mode = antenna mode

DUT + Wiring can act like an antenna by common mode current

What you should learn from Part 1

• What are the two sides of EMC? Emissions & Immunity

• What is the difference between narrowband and broadband? Broadband noise is ~ constant over large frequency, narrowband is at 1 frequency

• Name 2 types of broadband noise Coherent & Incoherent

• Name 3 types of narrowband modulation AM, FM, Pulse

• How does 60 Hz switching of a light make noise at 1MHz that interferes with AM radio? Harmonics in AM band repeating at 60Hz

• How does a cell phone operating at GHz frequency make an audio frequency noise in a speaker? Pulse modulation of carrier

• What is the difference between common and differential mode? Common mode is same current on both wires, differential is opposite current on both wires

• How do we get rid of conducted problems? Reduce differential mode

• How do we get rid of radiated problems? Reduce common mode

• What are three ways to measure or introduce electromagnetic noise? Direct conduction, current injection, capacitive coupling, radiation

Part 2: The stuff that fixes EMC

What you should learn from Part 2

• What are two methods to reduce radiated emissions?

• Why do we care if a DC signal is produced in an electronic circuit?

• What are two ways electrostatic discharge can affect electronics

• What are two ways that electromagnetic noise can be introduced into circuits

• How does a radio transmitter making signals at hundreds of MHz make a DC signal in an electronic circuit?

• What basic electronic structure leads to EMC problems?

• What limits the effectiveness of a capacitor, an inductor

• What are three ways to influence EMC of electronic circuits

Mitigating Emissions

• Add FiltersInductors (chokes), capacitors, resistors

• Add ShieldingEnclosed metal box, ground plane, conductive coating

• Add transient suppressionVaristors, rectifier diode, Zener diode (Transorb® / TVS)

• Add RF absorber material(B2 stealth bomber)

Elements of Basic Current Probe

Rogowski Coil With Ferrite Core Shielded Current Probe (Similar to

CISPR 25/CISPR 16 Probe)

Conductive Shield

Ferrite Core Coil Grounding Point

(a) (b)

Plastic Hinge

Conductive Shield

Ferrite Core Coil Grounding Point

(a) (b)

Plastic Hinge

Figure 3. Construction of the shielded current probe

(a) (b) (c)

(d) (e) (f)

(g)

Construction of Candlestick Current Probe

Emissions: Dimmer SwitchBroadband switching circuit

47kžTrigger

0.062µF

14.8µH

0.062µF

Thyristor

Dimmer Switch DemonstrationChopped 60Hz Sine Wave Acts as Broadband Source

Time

Magnitude of

noise at fixed

frequency

Emissions: Dimmer Switch

Filtering used in Dimmer switch

47kžTrigger

0.062µF

14.8µH

0.062µF

Thyristor

Low Pass Filter

Low Pass Filter

Emissions: Dimmer Switch

Filtering used in Dimmer switch

Low Pass Filter

Broadband NoiseFiltered Noise (high frequency removed)

Filter inputFilter output

Light dimmer filter is intended to prevent noise

from going back out onto power lines

Improving Immunity(see list for mitigating emissions)

• Add FiltersInductors (chokes), capacitors, resistors

• Add ShieldingEnclosed metal box, ground plane, conductive coating

• Add transient suppressionVaristors, rectifier diode, Zener diode (Transorb® / TVS)

• Add RF absorber material(B2 stealth bomber)+

• Go DigitalGet MP3’s and HD radio

Output

DC Supply

Trigger High Voltage Transformer

Rectifier

USB on normal Wakeup

USB on ESD Wakeup

Common mode current on keyboard cable

Current on Row and column circuits

Pulsed Radiation from ESD

Parasitic capacitance to harness

Impinging electromagnetic pulse

Conductive surface

Induced current reacting to wavefront

Magnetic coupling into keyboard loop

Common mode excitation

Fix with shielding Fix with bead

Current probe measurementsJust the keyboard

Keyboard with foil

Keyboard with foil+ bead

How to immunize the keyboard

Number of

ESD trigger

clicks

Beads and

Torroid on

Keyboard

Cable?

Foil Under

Keyboard?

Distance to wake

up computer

1 N N 12” to 15”

1 Y N 6” to 9”

3 to 5 Y Y <3”

1 N Y 0 to 3”

Communications transmissions as a source of noise

•How does a 1.9GHz cell phone signal contain audio information at 0-20kHz?

•We need to transmit 0-20kHz audio data in some means other than yelling from the top of our house. However an antenna to transmit 20kHz would be 3.75km long.

Time (mS)

Cell Phone Signal

f = 1.9GHz

Signal Strength at 1.9GHz

Time (mS)

Pulse Modulation

Time (mS)

Cell Phone Signal

f = 1.9GHz

Audio device with analog output

Speaker assembly with integrated amplifier

Cell Phone

Output of amplifier during cell phone transmission

Output of amplifier during hand radio key-on-off

P

N

How transistor circuits are susceptible to noise

Injected noise

p-n junction

Rectified noise with DC value

P

N

N

n

n

p

n

n

p

Follow the p-n junctions to find possible loops p-n-p-n-p-n… or n-p-n-p-n-p…

Inductive coupling of magnetic field can produce loop bias current with dc value due to p-n junction

Common mode current can be induced by radiation and will produce a bias current due to p-n junction

N

P

P

n

n

p

p

p

n

P

N

N

n

n

p

n

n

p

Transistors are likely to be biased

Inductive coupling of magnetic field can produce loop bias current with dc value due to p-n junction

Common mode current can be induced by radiation and will produce a bias current due to p-n junction

Amplifier Circuit

Source: UTC TDA2822 datasheet

n p

p

n

np

n

pp

n

pn

np

n

pn

n

n

pn

p

pn

n

np

pn

pn

np

p

pn

p

np

Possible loop for injection of noise

Amplifier Circuit

n

n

p

p

n

Amplifier Circuit

Fixing the problem by reducing the loop size or eliminating it

REAL WORLD EFFECTS

Component Terminology

• Parasitics: unintentional capacitance or inductance

• ESR: Equivalent Series Resistance of a capacitor

• Dielectric: the material in a capacitor which polarizes when charge is applied

• Dielectric Leakage: conduction current through a dielectric

• Ferrite: the material in an inductor through which magnetic flux flows

• Ferrite Beads: typical surface mount inductor components

What happens when real components are used for a filter?

Inductor or resistor Capacitor

“Parasitic” capacitance between the

turns of an inductor shunt current

around the inductor and thus counters

the high impedance of the inductor

Inductance of the capacitor leads

counters the low impedance of the

capacitor

Above some frequency expected filter

characteristics break down because of

these effects

Real inductors and capacitors have

resonant frequency due to parasitics

Impedance

of inductance

only

Impedance of

capacitance

only

1

10

100

1000

10000

1.E+06 1.E+07 1.E+08 1.E+09

Frequency (Hz)

Imp

ed

an

ce

(O

hm

s)

-180.00

-135.00

-90.00

-45.00

0.00

45.00

90.00

135.00

180.00

Ph

ase

An

gle

(D

eg

)

|Z|

/_ Z

ResonancePhase of Inductance

Phase of Capacitance

Phase angle of impedance reveals dominant characteristic

Above the resonant frequency, an inductor behaves as a

capacitor and a capacitor behaves as an inductor

Typical inductor characteristic

Inductor Capacitor

Resistive component is frequency and temperature dependent.

Power losses in the dielectric of the capacitor or the ferrite of the

inductor change with frequency and temperature.

ESR

Other real world effects

What you should learn from Part 2

• What are two methods to reduce radiated emissions? Shielding, filters

• Why do we care if a DC signal is produced in an electronic circuit? Many circuits use DC signals to accomplish their task

• What are two ways electrostatic discharge can affect electronics can blow them up or cause them to react improperly

• What are two ways that electromagnetic noise can be introduced into circuits by loops and by common mode current

• How does a radio transmitter making signals at hundreds of MHz make a DC signal in an electronic circuit? By rectification at p-n junctions

• What basic electronic structure leads to EMC problems? p-n junctions

• What limits the effectiveness of a capacitor, an inductor parasitic inductance and capacitance

• What are three ways to influence EMC of electronic circuits reduce loops, add filters, add shielding, watch out for p-n junctions.