EMC Basics concepts. Summary. Basic Principles Specific Units LC Resonance Radiating element Emission Spectrum Susceptibility Spectrum Notion of margin Impedance Conclusion. Basic principles. CONDUCTED AND RADIATED EMI. Conducted mode. Radiated mode.
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EMC Basics concepts
Basic principles
CONDUCTED AND RADIATED EMI
Conducted mode
Radiated mode
The VDD supply propagates parasits
The EM wave propagates through the air
Power Integrity (PI)
Electromagnetic Interference (EMI)
THE “EMC” WAY OF THINKING
Specificunits
Distinguish contributions of small harmonics
dB
Volt
Freq (Log)
Time
Cover very large bandwidth
Frequency measurement
Fourier transform
Spectrum analyser
AMPLITUDE IN DB VS. FREQUENCY IN LOG
Time domain measurement
Oscilloscope
Specific units
Milli
Volt
Volt
dBV
dBµV
100
1
10
0.1
For example dBV, dBA :
1
0.01
0.1
0.001
Extensive use of dBµV
0.01
0.0001
0.001
0.00001
EMISSION AND SUSCEPTIBILITY LEVEL UNITS
Voltage Units
Wide dynamic range of signals in EMC → use of dB (decibel)
Power
(Watt)
Power
(dBm)
1 MW
1 KW
1 W
1 mW
Exercise: Specific units
1 µW
1 mV = ___ dBµV
1 W = ___ dBm
1 nW
EMISSION AND SUSCEPTIBILITY LEVEL UNITS
Power Units
The most common power unit is the “dBm” (dB milli-Watt)
IC-EMC: 0dbm in 50
Tools > dB/Unit converter
LC Resonance
THE CHIP IS A LC RESONATOR
f= ___
Impedance (Ω)
Tools > LC resonance
Eurodots > z11-dspic-vdd_10-vss_9.z
Impedance measurement between Vdd and Vss
Frequency (Hz)
Radiating Element
RADIATED EMISSION
h
Radiating Element
NEAR FIELD/FAR FIELD
Near-field region
Far-field region
100 MHz : Rlimit =____
LC Resonance
THE BOARD IS A RESONATOR
Impedance (Ω)
Eurodots > z11-board-d21on.z
Frequency (Hz)
EMISSION LEVEL VS. CUSTOMER SPECIFICATION
EMC compatible
Specification example for an IC emission
Parasitic emission (dBµV)
80
70
60
50
Measured emission
40
30
20
10
0
-10
1
10
100
1000
Frequency (MHz)
Not EMC compliant
Customer's specified limit
EMC compliant
LOW PARASITIC EMISSION IS A KEY COMMERCIAL ARGUMENT
Emission
FM
GSM
RF
100
dBµV
Supplier
A
80
60
Supplier
B
40
20
0
10
100
1000
Frequency(MHz)
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
10
0
-10
A very low energy produces a fault
-20
-30
-40
1
10
100
1000
Frequency (MHz)
Notion of margin
Parasitic emission (dBµV)
Nominal Level
Design Objective
WHY A MARGIN ?
Notion of margin
INFLUENT PARAMETERS ON IC EMC
Std deviation = 1.7 dB
K. P. Slattery et al., “Modeling the radiated emissions from microprocessors and other VLSI devices”, IEEE Symp. on EMC, 2000.
H. Huang and A. Boyer (LAAS-CNRS)
Notion of margin
INFLUENT PARAMETERS ON IC EMC
Ioff/Ion MOS
32-nm
PhD A. C. Ndoye, INSA, 2010
Immunity vs. ageing (LTOL)
R,L,C VS. FREQUENCY
Impedance profile of:
Schematic diagram:
R,L,C VS. FREQUENCY
Impedance profile of:
Schematic diagram:
R,L,C VS. FREQUENCY
Impedance profile of:
Schematic diagram:
Characteristic Impedance
Coaxial line
Microstrip line
Link to conductor geometry and material properties
lossless
conductor
Equivalent electrical schematic
CONDUCTOR IMPEDANCE OR CHARACTERISTIC IMPEDANCE Z0:
Characteristic Impedance
IMPEDANCE MATCHING
Why impedance matching is fundamental ?
IC-EMC
Impedance>
impedance_mismatch.sch
Not adapted:
Adapted:
Voltage
Voltage
time
time
Characteristic Impedance
Small conductor
Large conductor
CHARACTERISTIC IMPEDANCE Z0:
What is the optimum characteristic impedance for a coaxial cable ?
Or ?
Ideal values:
Cable examples:
Characteristic Impedance
50 OHM ADAPTED SYSTEMS
Spectrum analyzer
Tem cell
Waveform generator
Amplifier
Tools > Interconnect parameters