fundamentals of emccandace suriano, john suriano, “emc war stories: letters from home part...
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FUNDAMENTALS OF EMC
Candace Suriano
John Suriano
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Special Thanks to our Sponsor
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Helpful books on EMC
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Helpful books on Signals
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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
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How to have a bad day
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Overview
•What is EMC and Who Cares about it?
•How Do People Measure EMC?
•Key Elements of EMC
•EMC for Everyone
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Part 1: The stuff that makes EMC
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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?
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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?
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What is EMC? Side 1
Don’t Make Noise
•EMISSIONS
Reduce the noise made by
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What is EMC?
Don’t Blow Up
•IMMUNITY
Preventing malfunction due to EM interference
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Who Cares About EMC?
•Governments (FCC, EU,CCC)
•People on airplanes
•Automobile Manufacturers
•Anyone who gets interference on their radio
•Hospitals
•Lawyers $$$
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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
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What you need to know to work on EMC
•Electromagnetics
•Signal Processing
•Communications
•Analog Electronics
•Digital Electronics
•PCB Layout
•Software
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What is involved in the study of EMC?
• Electromagnetics
• Signal Processing
• Electronics
• Communications
Source: Agilent.com
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Types of EMC Tests
• Emissions• Radiated Emissions
• Conducted Emissions
• Conducted Transients
• Immunity• Radiated Immunity
• Conducted Immunity
• Electrostatic Discharge
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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
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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?
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Measurement FacilitiesReverberation Chamber
Source: www.ets-lindgren.com
Source: www.walmart.com
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Measurement FacilitiesSemianechoic and Anechoic Chambers
Source: www.de.afrl.af.mil
Source: www.epg.army.mil
Source: www.ets-lindgren.com
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EMC Equipment
•Antennas and Probes
•EMI receivers and spectrum analyzers
•Artificial Networks
•Oscilloscopes
•Transient generators
•ESD guns
•Power amplifiers
•Standards, specifications and procedures
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1MHz 10MHz 100MHz 1GHz 10GHz
AM Radio FM Radio Cell Phones Mobile Radios
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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
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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
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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
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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
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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
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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)
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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)
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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
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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
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Narrow Band Signals
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Narrow Band Signal Modulation
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Narrow Band Noise
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Types of broadband noiseSwitching Transitions
RC Transitions
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Square Wave
Fundamental
Harmonics from a signal can produce noise at higher frequencies
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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
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Sine (CW)
Continuous wave signal can produce noise at only one frequency
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Exponential Decay
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How do signals get from one device to another?
•Conduction: ESD and transients
•Capacitive Coupling
•Inductive Coupling (Transformer)
•Radiation
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How to transmit noise
Magnetic coupling(loops)
Electric coupling(plates)
Radiation(wires)
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The Key to EMC?
• Differential Mode Current
-Conducted Emissions and Immunity
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The Key to EMC?
• Common Mode Current
-Radiated Emissions and Immunity
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Common mode = antenna mode
DUT + Wiring can act like an antenna by common mode current
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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
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Part 2: The stuff that fixes EMC
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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
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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)
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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
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Figure 3. Construction of the shielded current probe
(a) (b) (c)
(d) (e) (f)
(g)
Construction of Candlestick Current Probe
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Emissions: Dimmer SwitchBroadband switching circuit
47kžTrigger
0.062µF
14.8µH
0.062µF
Thyristor
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Dimmer Switch DemonstrationChopped 60Hz Sine Wave Acts as Broadband Source
Time
Magnitude of
noise at fixed
frequency
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Emissions: Dimmer Switch
Filtering used in Dimmer switch
47kžTrigger
0.062µF
14.8µH
0.062µF
Thyristor
Low Pass Filter
Low Pass Filter
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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
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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
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Output
DC Supply
Trigger High Voltage Transformer
Rectifier
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USB on normal Wakeup
USB on ESD Wakeup
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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
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Current probe measurementsJust the keyboard
Keyboard with foil
Keyboard with foil+ bead
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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”
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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
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Time (mS)
Cell Phone Signal
f = 1.9GHz
Audio device with analog output
Speaker assembly with integrated amplifier
Cell Phone
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Output of amplifier during cell phone transmission
Output of amplifier during hand radio key-on-off
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P
N
How transistor circuits are susceptible to noise
Injected noise
p-n junction
Rectified noise with DC value
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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
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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
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Amplifier Circuit
Source: UTC TDA2822 datasheet
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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
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n
n
p
p
n
Amplifier Circuit
Fixing the problem by reducing the loop size or eliminating it
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REAL WORLD EFFECTS
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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
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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
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Real inductors and capacitors have
resonant frequency due to parasitics
Impedance
of inductance
only
Impedance of
capacitance
only
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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
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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
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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.