EMC Basics concepts

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EMC Basics concepts
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Summary
1. Basic Principles 2. Specific Units 3. Fourier
Transform 4. Emission Spectrum 5. Susceptibility
Threshold 6. Notion of margin 7. Impedance 8.
Conclusion
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EMC environment
The EMC way of thinking
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Specific units
Amplitude in dB vs. Frequency in Log
Time domain measurement
Oscilloscope
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Specific units
Emission and susceptibility level units
Voltage Units
Wide dynamic range of signals in EMC ? use of dB
(decibel)
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Specific units
Emission and susceptibility level units
Power Units
The most common power unit is the dBm (dB
milli-Watt)
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Specific units
Fourier transform
Why Frequency domain is so important ?
Time domain
Frequency domain
Only high level harmonics contribution appears
Contribution of each harmonic appears
Low level harmonics contribution
Users specification
FFT
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Emission spectrum
Emission level has to be lower than customer
specification
EMC compatible
Parasitic emission (dBµV)
Specification for an IC emission
80
70
Aggressor IC
60
50
Measured emission
40
30
20
10
Radiated emission
0
-10
1
10
100
1000
Frequency (MHz)
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Emission spectrum
Low parasitic emission is a key commercial
argument
FM
GSM
RF
100
dBµV
Supplier A
80
60
Supplier B
40
20
0
10
100
1000
Frequency(MHz)
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Emission spectrum
Examples of Conducted and Radiated emission levels
dBµV
80
Class 4
70
60
Class 5
50
40
3M
30M
30K
300K
Conducted emission level (CISPR25)
CISPR 25 Radio disturbance characteristics for
the protection of receivers used on board
vehicles, boats, and on devices Limits and
methods of measurement
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Susceptibility spectrum
Immunity level has to be higher than customer
specification
Immunity level (dBmA)
Specification for board immunity
Current injection limit
50
40
30
Measured immunity
20
Victim IC
10
0
-10
A very low energy produces a fault
-20
-30
-40
1
10
100
1000
Frequency (MHz)
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Notion of margin
What is a margin ?

• To ensure low parasitic emission ICs supplier has
  to adopt margins

• Margin depends on the application domain

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Notion of margin
Auto-compatibility issue ?
EMC Level (dB)
Susceptibility level
50
High risk of interference
40
Aggressor IC
30
Safe interference margin
20
Unsafe margin
10
0
-10
Victim IC
-20
Sum of perturbations
-30
-40
1
10
100
1000
Frequency (MHz)
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Impedance
R,L,C vs. frequency
Impedance profile of

• 50 ohms resistor

• 100pF capacitor

• 10nH inductor

• a real 100 pF SMD capacitor

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Impedance real models
R, L, C components Examples
Ceramic capacitor
Inductor
Carbon resistor
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Impedance
Conductor impedance or Characteristic Impedance
Z0
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Impedance
Impedance matching
Why impedance matching is fundamental ?
Not adapted the line suffers ringing, insertion
losses
Adapted the line is transparent
Voltage
Voltage
time
time
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Impedance
Characteristic Impedance Z0
What is the optimum characteristic impedance for
a coaxial cable ?
Or ?
Ideal values

• Maximum power Z0 ___?

• Minimum loss Z0 ___ ?

Cable examples

• EMC cable (compromise between power and loss)
  Z0 ___ ?
• TV cable Z0 ___ ?
• Base station cable Z0 ___ ?

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Impedance
50 ohm adapted systems
Spectrum analyzer
Tem cell
Waveform generator
Amplifier
Gtem
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Conclusion

• Key words of EMC for integrated circuits have
  been presented
• The origin of parasitic emission in Ics has been
  illustrated
• The trend to decrease supply voltages increase
  the IC susceptibility
• Specific units used in EMC have been detailed
• The Fourier Transform is a very important tool
  for the characterization of EM signals
• The notion of impedance has been introduced