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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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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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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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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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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