Radiated Emission from Signal
Traces Changing Reference Planes
Marcel van Doorn
Philips Innovation Services – EMC Center
September 2014
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EMC Europe 2014 Gothenburg, 1-4 September
Outline
Radiated Emission from Signal Traces Changing Reference Planes
• Introduction
• Modeling approach
• Simulation results and design guidelines
– Crossing 0, 1, and 2 planes
– Number of vias
– Via distance
– Plane distance
– Stitching vias at board edges
– Copper and dielectric losses
• Concluding remarks
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EMC Europe 2014 Gothenburg, 1-4 September
Introduction
Trends and needs
• Trends
– Faster components  bandwidth Increase
– Shifting statutory emission requirements (CISPR 32)  from 1 to 6
GHz; to protect GHz communication bands
• Needs
– Designers need new high-speed design insights and guidelines to
make the right choices on PCB technology, cable & connector
technology, and shielding design
This paper focuses on new quantitative design guidelines for printed
circuit boards to control radiated emission of signal traces changing
reference planes.
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EMC Europe 2014 Gothenburg, 1-4 September
Introduction
Signal trace changing reference planes
Source: Howard Johnson, “High-Speed Signal Propagation: more
black magic” Chapter 5.5.5.1 Through-hole Via Induction
• Return current path when a signal trace changes reference planes
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EMC Europe 2014 Gothenburg, 1-4 September
Modeling approach
Board and via dimensions (in mm)
Board and via dimensions (in mm)
0.7
160
PCB
Hole
Cu pad
50 Ω source
10
50
via
Anti-pad
100
0.2
50
10
5
50 Ω load
EMC Europe 2014 Gothenburg, 1-4 September
0.45
0.125
Modeling approach
Source model
Rs
Es
Ii
Vs
Z0
Rl
Ltrans
Transmission line on PCB (microstrip):
Es = 1 V (100 MHz – 6 GHz)
Rs = Rl = Z0 = 50 Ω
Trace height h = 0.1 mm
Trace width W = 0.16 mm
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W
r = 4.7
h
Modeling approach
Simulation cases
S
S
S
Gnd
Gnd
Gnd
S
no plane crossing
1 plane crossing
Signal
via
Gnd return
via
S
• 2 planes crossing
• number of vias
• via distance
• plane distance
CST model of cross section with 1
signal via and 4 return vias (3 visible)
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Modeling approach
Simulation output: maximum radiation
Max E-field (dBuV/m)
60
50
40
CISPR 32
30
20
E-field
10
0
10
Radiation pattern at 1 GHz
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100
1000
Frequency f (MHz)
10000
Max E-field on sphere with radius 10 m as a
function of frequency
Simulation results and design guidelines
Crossing 0, 1, and 2 planes
S
100
Emax (dBuV/m)
80
b
a
60
Gnd
S
b
Gnd
S
40
S
20
1 plane, no via
1 plane, 1 via
2 planes, 1 via
0
-20
100M
9
a
c
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1G
f (Hz)
c
Gnd
Signal
via
Gnd
S
• Plane distance = 1 mm
10G • No return via
Simulation results and design guidelines
Emax (dBuV/m)
Number of vias
100
S
80
Signal
via
60
S
• Return via(s) at 0.7 mm
distance from signal via
• Plane distance = 1mm
40
20
1 return via
2 return vias
4 return vias
no return via
0
-20
100M
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Gnd
1 return
via
Gnd
1G
f (Hz)
10G
Simulation results and design guidelines
Via distance
S
100
Signal
via
Emax (dBuV/m)
80
60
• 1 return via at d = 0.5, 1
and 10 mm distance
from signal via
• Plane distance = 1mm
20
-20
100M
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S
40
0
EMC Europe 2014 Gothenburg, 1-4 September
Gnd
1 return
via
Gnd
return via @ 0.5 mm
return via @ 1 mm
return via @ 10 mm
1G
f (Hz)
10G
Simulation results and design guidelines
Emax (dBuV/m)
Plane distance
100
S
80
Signal
via
60
S
• 1 return via at 0.7 mm
distance from signal via
• Plane distance h = 1, 0.5
and 0.1 mm
40
20
0
-20
100M
12
h
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Gnd
1 return
via
Gnd
plane distance 1 mm
plane distance 0.5 mm
plane distance 0.1 mm
1G
f (Hz)
10G
Simulation results and design guidelines
Stitching vias at board edges
100
• Plane distance = 1 mm
Emax (dBuV/m)
80
60
20
0
-20
100M
13
• 4 vias at board corners
40
no return via
vias at board corners
vias @ 5 mm around edges
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1G
f (Hz)
• vias at 5 mm around
10G board edges
Simulation results and design guidelines
Emax (dBuV/m)
Copper and dielectric losses
100
S
80
Signal
via
60
• Return via at 0.7 mm
distance from signal via
• Plane distance = 1mm
• Dielectric loss: tan δ = 0.02
20
-20
100M
14
S
40
0
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Gnd
1 return
via
Gnd
lossfree
Cu lossy
Cu lossy + FR4 lossy
1G
f (Hz)
10G
Concluding remarks
• Signal frequencies are increasing and statutory radiated
emission requirements are shifting to higher frequencies.
• The design community needs new HF EMC design guidelines.
• In this paper design guidelines are presented to reduce the
radiated emission of signals changing reference planes on PCBs
up to 6 GHz.
• Earlier papers* contain more quantitative EMC design guidelines
at board, cable and enclosure level (based on same modeling approach)
*
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1. Van Doorn, “EMC Expert System for Architecture Design”, EMC Korea Jeju Island 2011
2. Van Doorn, “EMC Design Guidelines for Electrical Architectures”, EMC Europe Brugge 2013
EMC Europe 2014 Gothenburg, 1-4 September
Acknowledgement
This work is supported by the Eniac Joint Undertaking project
Enlight: Energy efficient and intelligent lighting systems
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