Deriving Design Limits using the Expert System Algorithms
Todd H. HubingMichelin Professor of Vehicular ElectronicsClemson University
Printed Circuit Board Layout
Automotive EMC
System-Level Extensions
EMC Expert Systems
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PCB Expert System Method
Source Model Antenna ModelCoupling Path Model
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PCB Expert System Method
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Differential-Mode Radiation
Coupling to I/O Radiation
Voltage-Driven Common-Mode Radiation
Current-Driven Common-Mode Radiation
Power Bus Radiation
PCB Expert System Emissions Models
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Algorithms Locate Hard-to-Find Problems
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Expert System Algorithms are constantly answering the question,
How bad could it be?
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Effect of Extended Cable on Ground
l
1 m
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NCMS Board Analysis using Expert System Algorithms
• 8 clock buffers
• 28 load capacitors
• 32 decoupling capacitors
• Clocked at 50 MHz
• No heatsink
• Size: 3” by 2”, 6 layers
• Powered with one cable
U7U2
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Measurement vs. Calculation: 1-nF Load
x
y
z
h
a
b
Ms
Ms
Ms
Ms
120 ( )min( , )
i
r
I hE Q fa b rε
= ⋅ ⋅
11 1 1( )
d c comp
Q fQ Q Q
−⎛ ⎞
= + +⎜ ⎟⎜ ⎟⎝ ⎠
H. Shim and T. Hubing, “Estimating radiated emissions from the power planes in a populated printed circuit board,” IEEE Trans. on Electromagnetic Compatibility, vol. 48, no. 1, Feb. 2006.
Power Bus Radiation Model
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x
y
z
h
a
b
Ms
Ms
Ms
Ms
Maximum Power Bus Radiation
( )( , , , , , , , ) 0,0rE f r h L W Vθ ϕ ε ω= ×
2sin_ _ 4
1.0
boardboard
l when lboard size factor
otherwise
λπλ
⎧ ⎛ ⎞ ≤⎜ ⎟⎪≡ ⎝ ⎠⎨⎪⎩
( )maxmax0,0 _ _E f V board size factor= × ×
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Maximum Power Bus Radiation( )maxmax0,0 _ _E f V board size factor= × ×
Max E-field at 3 m, (10 cm X 10 cm, V(0,0)=1 volts)
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Minimum Power Bus Voltage
( )minmax
0.0_ _FCC
EV
f board size factor=
×
Minimum voltage required to generate fields exceeding the FCC Class B limit
Expert System Field Calculation Performed in Reverse
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Minimum Power Bus Voltage (Board w/Cable)
( ) ( ) 76.237
)0,0(20,20 maxmax0 ××=××=
ohmV
kfIE θ
⎪⎩
⎪⎨⎧ ≤⎟
⎠⎞⎜
⎝⎛
≡otherwise
lwhenlfactorradcable cable
cable
0.14
2sin__
λλ
π
2sin_ _ 4
1.0
boardboard
l when lboard size factor
otherwise
λπλ
⎧ ⎛ ⎞ ≤⎜ ⎟⎪≡ ⎝ ⎠⎨⎪⎩
factorsizeboardfactorradcableEE ____min
××=
Cable To Floor
V(0,0) Power Bus Noise voltage
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Minimum Power Bus Voltage (Board w/Cable)
factorsizeboardfactorradcableEE ____min
××=
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Minimum Power Bus Voltage (Board w/Cable)
76.220
37____
max
min ×
××=
ohmfactorsizeboardfactorradcable
E
VExpert System Field Calculation
Performed in Reverse
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IC-Heatsink to Cable Coupling
~
CableEquivalent voltage
VCM
sinheat kCM DM
board
CV VC
=max
sin
0.2234 boardDM
heat k board cable
C rV EC F F
= × ×To Floor
To Floor
~VDM Noise voltage
Heatsink
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IC-Heatsink to Cable Coupling20cm
20cm
100cm
5cm5cm
1cm
Spacing between heatsink and board is 1 cm
sin 0.43 5.14
heat k
board
C pFC pF
=
=
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IC-Heatsink to Cable Coupling
20cm20cm
100cm
5cm5cm
1cm
Spacing between heatsink and board is 1 cm
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Conclusion
Many of the EMC expert system algorithms canbe solved “manually” in reverse to relatemaximum allowable emissions to maximumallowable voltages or currents on a printed circuitboard.
This can be a useful for trouble shooting circuitboards because voltages and currents measuredon the board can be related to possible emissionssources.
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