Deriving Design Limits Based on Expert System Algorithms · 2012. 5. 28. · PCB Expert System...

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

UMR EMC Consortium Meeting November 14, 2007 2

PCB Expert System Method

Source Model Antenna ModelCoupling Path Model


PCB Expert System Method


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


Algorithms Locate Hard-to-Find Problems


Expert System Algorithms are constantly answering the question,

How bad could it be?


Effect of Extended Cable on Ground

l

1 m


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



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


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= × ×


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)


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


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



factorsizeboardfactorradcableEE ____min

××=



76.220

37____

max

min ×

××=

ohmfactorsizeboardfactorradcable

E

VExpert System Field Calculation

Performed in Reverse


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


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

=

=


IC-Heatsink to Cable Coupling

20cm20cm

100cm

5cm5cm

1cm

Spacing between heatsink and board is 1 cm


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.


Deriving Design Limits Based on Expert System Algorithms · 2012. 5. 28. · PCB Expert System...

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