Vesa Linja-aho presents information on electromagnetic compatibility (EMC). He discusses how all electric devices should operate without interfering with other devices or being susceptible to normal interference. He covers common sources of electromagnetic interference and techniques to prevent issues, such as proper layout design, filtering of interfaces, and shielding of components. Linja-aho emphasizes that EMC should be considered from the beginning of a design process, not as an afterthought.

1. Electromagnetic Compatibility
Vesa Linja-aho – 2012-07-19

2. Me
 Senior Lecturer in Automotive Electronics at
Metropolia UAS
 Background: M.Sc. in Electromagnetics and
Circuit Theory, Helsinki University of Technology
 Worked as researcher, lecturer and journalist.
 Interested in Open Educational Resources and
Electric Work Safety.
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3. Metropolia UAS
 In Finland, we have two kinds of institutions of
higher education
 University: Bachelor (3 yr), Master (2 yr), PhD
(3-4 yr)
 University of Applied Sciences (UAS): Bachelor
(4 yr) and Master (2 yr)
 Metropolia is the largest UAS in Finland
 Automotive engineering education:
 Formula Student –team
 Electric Raceabout (ERA)
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4. Studying in Finland
 Metropolia unfortunately does not have
automotive engineering degree programmes in
English, unfortunately.
 But we have other interesting programmes:
http://www.metropolia.fi/en/
 In Finland, we do not have tuition fees (some
universities charge a tuition fee from non-EEA
citizens, but not Metropolia).
 The application time is at spring.
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5. EMC = Electromagnetic Compatibility
 All electric and electronic devices should be
designed so that they
 will accept any normal interference
 won’t interfere other devices.
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6. Everyday Examples?
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7. Everyday Examples
 The ”GSM song”
 FM radio crackling when your neighbor drills a
hole on his wall.
 FM radio clicking when fluorescent tubes start.
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8. Not-so-everyday Examples
 Electric wheelchair turns in the water when a
police officer pushes talk button in the police
boat radio.
 Piezoelectric cigarette lighter opens barrier at a
parking lot.
 Starting a welding transformer causes the
central computer to crash (in another building).
 The roof and central locking system react to
cellphone.
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9. Electromagnetic Interference (EMI)
 Natural interference: cosmic radiation and
thunderstorm.
 Technical interference:
 Electrostatic discharge (ESD)
 Digital circuits
 Changes in the mains voltage
 Wireless communication
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10. Coupling Mechanisms
 Conducting
 Capacitive coupling (via electric field)
 Inductive coupling (via magnetic field)
 Electromagnetic waves
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11. Coupling Mechanisms
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12. How to Fight EMI?
 Prevent the emergence of interference
 Cut the path of propagation
 Improve the tolerance for the interference
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13. Countermeasures in Practice
 Layout design and position of the wires
 Symmetrical transmission
 Filtering
 Using digital electronics
 Using optical transmission
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14. Brief Physical Background
 An electric charge creates an electric field.
 Electric current or changing electric field creates
a magnetic field.
 Changing magnetix field induces a voltage into a
wire.
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15. Capacitive coupling = Coupling via Electric
Field
Countermeasures
 Metallic enclosing
 Increasing the distance between wires
 Positioning the wires near the ground plane
 Decreasing the impedance level
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16. Inductive Coupling = Coupling via Magnetic
Field
Countermeasures
 Layout design
 Decreasing the impedance level
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17. EMC is not a Separate Matter
 The risky way: design the product and fix the
EMC issues afterwards.
 The safe way: keep EMC in mind during the
whole design process
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18. Common Mode vs. Differential Signal
 Common mode signal together with the ground
plane causes a large loop between circuits.
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19. Three-level Protection
 Layout design
 Interface filtering
 Metallic enclosing
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20. Do we need protection?
 In simple non-critical devices, the layout design
is often enough.
 Especially, if there are no cables to/from the
device.
 About 90 % of post-design EMC-problems are
caused by poor layout design!
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21. Good layout design
 Split the system in parts
 Think the ground plane as a large current
conducting path.
 Choose grounding points well and minimize the
grounding impedance.
 Remember that every conducting part can carry
interfering currents!
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22. Splitting the system in parts
 Decide which parts are critical vs. non-critical.
 Place the parts which are neither sensitive nor
sources for interference, into separate locations
even on their own circuit boards.
 For example, linear power supplies, non-clocked
logic circuits and power amplifiers are usually
immune to interference.
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23. Grounding
 The ground plane is non-ideal. The correct
grounding style depends on the circuit.
 Single-point grounding is common in switching-
mode power supplies. It prevents interfering
voltages caused by currents through common
impedances.
 But: on large frequencies, the wires act as
transmission lines!
 Multi-point grounding. Works well on large
frequencies. Each circuit has its own ground,
and the grounds are interconnected with short
wires.
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24. Rule of thumb for grounding
 < 1 MHz: Single-point grounding
 > 10 MHz: Multi-point grounding
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25. Using a ground plane
 If you use a multilayer PCB, using a ground
plane is possible and recommended.
 With RF circuits and fast digital circuits using the
ground plane is practically mandatory.
 What is the purpose of the large ground plane?
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26. The purpose of the ground plane
 The main purpose is to provide low grounding
impedance.
 The secondary purpose is to act as a shield.
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27. Crosstalk
 Two wires on the PCB are – unfortunately –
connected to each other capacitively and
inductively.
 In practice, there is no cross-talk if the distance
between wires is larger than 1 cm.
 Dropping the impedance and using the ground
plane will reduce crosstalk.
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28. Design Checklist
 Avoid long wires on the PCB board.
 Sensitive and interfering components should not
be placed near each other.
 Do not place sensitive parts near the edges of
the ground plane.
 Split the circuit in parts very carefully.
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29. Interfaces and filtering
 Most devices are interconnected to other devices
via a cable.
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30. Ferrite chokes
 Very common in data cables.
 Adds series inductance to cable.
 Effective on frequencies 1-1000 MHz
(approximately).
 Disadvantage: relatively low attenuation (10-20
dB).
 Advantage: easy to add afterwards.
 Ferrite choke attenuates also fast transients
caused by ESD.
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32. Mains filtering
 Example: an electric shock from computer
chassis.
 Maximum leak current 0,5 mA. (EN 60601-1-1)
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33. Cables
 Coaxial cable
 Twisted pair
 Shielded twisted pair
 The shield should be connected evenly – avoid
the pig tail mistake!
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34. Switches
Switches cause disturbance in two ways:
 Arcing
 Bouncing
  Use RC snubber
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35. Relays
 RC snubber + protective diode
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36. Electric motors
 Motors cause strong magnetic fields.
 If the motor has commutator or brushes, the
arcing causes wide-spectrum RF interference.
 Inverter-driven permanent magnet machines are
more EMC-safe.
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37. ESD protection
 Have you ever destroyed anything with ESD.
 What precautions you should take when handling
and installing an expensive graphics card to your
computer?
 MOSFET components are the most sensitive part
to ESD.
 The main method for ESD protection is
protective diodes.
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38. Legislation and Standards
 Harmonized by European Union
 EMC-directive 2004/108/EY
 Radio and telecommunications equipment
1999/5/EC
 Automotive EMC-directive 2004/104/EC.
 European standards and national laws.
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39. There are Plenty of Standards
 Many device types have their own standard.
 If there is no standard available, the general
standard is to be applied.
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40. EMC Testing
 EMI immunity
 EMI emissions
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41. EMC Testing Case Example: Electric Raceabout

42. Name surname 42

43. Thank you!
www.metropolia.fi/en/
www.facebook.com/MetropoliaAMK
firstname.surname@metropolia.fi