EMC’09/Kyoto
22Q3-4
A New Approach for Measurement of
Common-mode Voltage Fluctuation with WBFC
Yuichi Mabuchii)ii),1, Atsushi Nakamura iii), Takanori Uno iv), Tohlu Matsushima i)v), and Osami Wadai)
i)
Department of Electrical Engineering, Kyoto University
Kyoto Daigaku Katsura, Nishikyo-ku, Kyoto 615-8510, Japan
1
yuichi.mabuchi.wz @hitachi.com
ii)
Hitachi Research Laboratory, Hitachi Ltd.
1-1 Omika-cho 7, Hitachi-shi, Ibaraki, 319-1292, Japan
iii)
Renesas Technology Corp.
5-20-1 Josuihontyo, Kodaira-shi, Tokyo, 187-8588, Japan
iv)
Corporate R & D Department, DENSO CORPORATION
1-1, Showa-cho, Kariya-shi, Aichi-ken, 448-8661, Japan
v)
Graduate School of Natural Science and Technology, Okayama University
3-1-1, Tsushima-naka, Okayama, 700-8530 JAPAN
Spectr um anal yzer
Abstract— Common-mode current can be a main cause of
electromagnetic interference in electronic control units (ECUs).
In this paper, a new approach to measure the common-mode
voltage fluctuation on ECU with workbench Faraday cage
method (WBFC) is proposed. It is verified theoretically and
experimentally that the values of the common-mode voltage
fluctuation obtained from the proposed WBFC method have
correlation with the value of the common-mode current
measurement with the CISPR 25 method.
Key words: common-mode current, electromagnetic
compatibility, electromagnetic interference, printed circuit board
I. INTRODUCTION
In electronic control units (ECUs), electromagnetic
compatibility (EMC) and electromagnetic interference (EMI)
are issues to be solved. In the paper [1], it is shown that the
value of the electromagnetic radiation can be predicted
adequately from the consideration of the amount of the
common-mode current flowing on the conductor pattern of the
PCB. In the paper [2], two mechanisms of common-mode
current generation, which are `voltage-driven type’ and
`current-driven type’ is proposed and it is shown that they
effectively excite the common-mode current for the ECU to
which a wire-harness is attached.
One of the regulations is IEC CISPR 25 for automobile
ECUs [3]. The measurement setup of CISPR 25 is shown in
Fig. 1. In this setup, a wire-harness whose length is about
1500 mm is attached to the equipment under test (EUT). Both
the power and GND lines of the wire-harness are terminated
with line impedance stabilization network (LISN) at the each
end of these lines. There are limits for the common-mode
current and ECUs need to be lower level than these limits.
In the CISPR 25 measurement setup, the wire-harness is
located at 50 mm above the reference GND plane and its
common-mode impedance usually takes about 100 to 150 ohm.
The each end of the power and GND lines of the wire-harness
is terminated with LISN whose impedance is 50 ohm, so the
Reference
GND
Current pr obe
EUT
50mm
50mm
Battery
Wire-Harness
50mm
1500mm
LISN
Fig. 1 The CISPR 25 measurement setup for the common-mode
current on the wire-harness.
common-mode terminal impedance of the wire-harness is 25
ohm. Therefore some amount of the common-mode current is
reflected at the LISN. This causes standing waves and the
value of the common-mode current depends on both of the
measured frequency and the position on the wire-harness. And
the measurement has to be executed in shielded rooms to
avoid the noise from outside.
In this paper, we propose a new measurement approach to
evaluate the common-mode voltage fluctuation on ECUs with
workbench Faraday cage method (WBFC) [4]. This
measurement approach can be executed more easily than that
of CISPR 25 because it does not have to be executed in the
shielded room. In this paper, it is shown that the values of the
common-mode voltage fluctuation evaluated by using our
proposed approach have clear correlations with the values of
the common-mode current evaluated by using the CISPR 25
measurement setup for the very high frequency (VHF: 30 to
300MHz) range that is important for automotive ECUs.
II. A COMMON-MODE VOLTAGE MEASUREMENT TECHNIQUE
BY USING WBFC
First, we consider the measurement setup of the CISPR 25.
In the papers [5][6], the mechanism of the common-mode
current generation is researched for the case of the PCB that
has a signal line and GND line as the return path of the signal.
We expand the considerations in these papers to the case of
the PCB to which a wire-harness is attached. An approximate
Copyright © 2009 IEICE
425
EMC’09/Kyoto
Noise Source x
0
x
PCB (Area I)
(Micro-controller)
Vb0
1
V1I ( x)
2
V2I ( x)
22Q3-4
lI
x
II
b
I
u
I
I
L11
L12
I
LI22 L12
I
C22
C12I
C11I C12I
Vb0
50 ohm
Termination
II
II
L11
L12
II
LII22 L12
§ 1
¨
¨ 1 G II
¨ 1
©
GI
V2I ( x )
I
I
L11
L12
I
LI22 L12
V1II ' ( x )
100Ω
V2II ' ( x)
100Ω
2
VbII ( x), VuII ( x)
I
C22
C12I
C11I C12I
G II
II
II
L11
L12
II
LII22 L12
Spectrum
Analyzer
Hybrid Balun
C22II C12II
C11II C12II
Fig. 3 An approximate equivalent circuit for the proposed WBFC
method. In the same manner in Fig. 1, VI1(x), VI2(x), VII’ 1 (x), and
VII’ 2 (x) mean voltages of each line. VIb (x) and VIIb(x) mean differential
-mode voltage of each area. VIu (x) and VIIu (x) mean common-mode
voltage of each area.
GI · I
¸§V1 ( x) ·
1 G I ¸¨¨ I ¸¸
1 ¸¹©V2 ( x) ¹
.
G II · II
¸§V1 ( x) ·
1 G II ¸¨¨ II ¸¸
1 ¸¹©V2 ( x) ¹
.
2
VbI ( x ), VuI ( x)
II
C22
C12II
C11II C12II
(1)
In the same way, the differential-mode voltage VIIb(x) and
common-mode voltages VIIu(x) in the area II have the relation
with the voltages VII1(x) and VII12(x) as shown in the next
equations:
§VuII ( x) ·
¨ II ¸
¨V ( x) ¸
© b
¹
V1I ( x )
Z cap
equivalent circuit for the power and GND lines of the CISPR
25 measurement setup is shown in Fig.2. When microcontroller is driving, through current is generated in the chip
and it flows on the power and GND lines as the differentialmode current. At the same time, the common-mode current is
generated by the voltage-driven or current-driven mechanisms
[2]. Considering these situations, there are differential and
common-mode voltage sources where micro-controller is
equipped, and they are described as Vb0 and Vu0, respectively.
The power and GND lines of the PCB are driven by the
mixture of these two voltage sources. The PCB is in the area I.
There are the power line numbered by 1 and the GND line
numbered by 2 in this area. The self-inductances and selfcapacitances for unit length of these lines are LI11, LI22, CI11,
and CI22, respectively. And the inductive and capacitive
interactions between the power and GND line are denoted as
LI12, and CI12, respectively. In the same way, the area II
corresponds to the power and GND lines of the wire-harness
and their self-inductances, self-capacitances, and the
interactions between them are described as LII11, LII22, CII11,
CII22, LII12, and CII12, respectively. At the point of x=lI+lII, each
of the power and GND lines of the wire-harness is terminated
with 50 ohm resistance, which means the termination with
LISN. At the point of x=lI, the bypass capacitor whose
impedance is Zcap is equipped. In the area I and II, the
voltages of the power and GND lines at the point of x are
described as VI1(x), VI2(x), VII1(x), and VII2(x), respectively.
The differential-mode voltage VIb(x) and common-mode
voltages VIu(x) in the area I have the relation with the voltages
VI1(x) and VI2(x) as shown in the next equations:
§ 1
¨
¨1 GI
¨ 1
©
Probe (Area II)
1
1
Vu0
G II
Coaxial Cable
lI
II
u
Fig. 2 An approximate equivalent circuit for the CISPR 25
measurementsetup. VI1 (x), VI2 (x), VII1 (x), and VII2(x) mean voltages
of each line. VIb(x) and VIIb (x) mean differential-mode voltage of
each area. VIu(x) and VIIu (x) mean common-mode voltage of each
area.
§VuI ( x) ·
¨ I ¸
¨V ( x) ¸
© b
¹
x
PCB (Area I)
V ( x), V ( x)
V ( x), V ( x)
GI
V2II ( x )
0
(Micro-controller)
V ( x)
1
2
I
b
Inside of the WBFC
x
Noise Source
II
1
Z cap
Vu0
lI lII
Wire-Harness (Area II)
(2)
In the equations (1) and (2), δ I andδ II are the balanceparameters for the PCB and the wire-harness, and they are
defined by the next equations:
GI
I
I
L11
L12
I
LI22 L12
G II
II
II
L11
L12
II
LII22 L12
C22I C12I
C11I C12I ,
C22II C12II
C11II C12II .
(3)
(4)
In Fig. 2, each voltage of the line VI1(lI), VI2(lI) in area I is
equal to the voltage VII1(lI), VII2(lI) in the area II at x=lI, and
from the equation (1), the voltages VI1(lI) and VI2(lI) are
defined with VIb(lI) and VIu(lI) as shown in the next equations:
V1I (lI ) V1II (lI ) VuI (lI ) GI
1 GI
VbI (lI )
,
(5)
1
V (lI ) V (lI ) V (lI ) VbI (lI )
1 GI
.
I
2
II
2
I
u
(6)
Substituting the values of VII1(lI) and VII2(lI) which are
determined in the equations (5) and (6) to the equation (2), the
common-mode voltage VIIu(lI) can be derived and it is shown
in the next equation:
G I G II
VuII (lI ) VuI (lI ) VbI (lI )
(1 G I )(1 G II )
.
(7)
Generally the conductors of the power and GND lines in the
wire-harness have same diameter and length each other, so the
self-inductances LII11, LII22 and self-capacitances CII11, CII22 of
the power and GND line take same values each other and the
balance parameter δ II of the wire-harness becomes 1.
Therefore from the equation (7), the common-mode voltage
VIIu(lI) on the harness at x=lI is derived as shown in the next
equation:
G 1 I
VuII (lI ) VuI (lI ) I
Vb (lI )
2(1 G I )
.
(8)
On the wire-harness, the values of common mode current Icm
is proportional to the common mode voltage VIIu(lI) defined in
the equation (8), which is shown in the next equation:
G 1 I
I cm v VuI (lI ) I
Vb (lI )
2(1 G I )
.
(9)
Next, we consider the measurement setup to evaluate the
common-mode voltage fluctuation with the WBFC method.
An approximate equivalent circuit is shown in Fig. 3. Two
measuring probes whose characteristic impedances are both
150 ohm are connected to the PCB instead of the wire-harness.
With these probes, the common-mode voltage fluctuations of
Copyright © 2009 IEICE
426
EMC’09/Kyoto
22Q3-4
p2
p6
p7
TABLE 1
Measurement conditions related to the positions of equipped
bypass capacitors and micro-controller.
Oscillator
Circuit
p10
p1
Package
p4
90 mm
p3
p5
p11
p12
p8
p9
Capacitor for
Voltage
Converter
are positions
of the bypath
capacitors
110 mm
Fig. 4 An image of the evaluation PCB. This PCB has two conductive
layers. Rectangular marks in this image mean the positions where bypass
capacitors are equipped.
the power and GND lines of the PCB are evaluated. Each
probe is connected to the 50 ohm coaxial cable at x=lII and a
100 ohm resistance is inserted between them to avoid the
reflection of the voltage wave. The other ends of the coaxial
cables are connected to the hybrid balun. These two inputted
signals from the coaxial cables are arithmetically averaged in
the hybrid balun and its output signal from the balun is
evaluated by a spectrum analyzer. By doing so, the
differential-mode voltage fluctuation is canceled and only the
common-mode voltage can be evaluated. Theoretical
consideration of the voltage fluctuation of the WBFC method
can be treated in the same way of the former consideration for
the CISPR 25 method. As show in Fig. 2, the voltages on the
probes are denoted as VII’1(x) and VII’2(x), respectively. The
voltage fluctuations of the power and GND lines at the point
of x=lI where the probes are connected to the PCB are defined
as the next equations:
V1II ' (lI ) VuI (lI ) GI
1 GI
VbI (lI )
,
(10)
1
V ' (lI ) V (lI ) VbI (lI )
1 GI
.
II
2
I
u
(11)
These voltages are detected by the probes, and the voltage
Vcom that is evaluated by the spectrum analyzer is proportional
to the arithmetically averaged value of these two voltages,
which is shown in the next equation:
Vcom v VuI (lI ) G I 1 I
Vb (lI )
2(1 G I )
(12)
By comparing the equation (12) to (10), it can be seen that the
common-mode voltage measured by the WBFC method has
clear correlation with the CISPR 25 method.
No.
MicroController
Equipped Bypass
Capacitor(s)
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
NMC
NMC
NMC
NMC
NMC
NMC
NMC
NMC
NMC
NMC
LMC
None
only p1
only p2
only p3
only p4
only p5
p6 and p7
p8 and p9
p4, p5, p10
p4, p5, p8, p9, p10, p11, p12
None
parameter is micro-controller. Two types of the microcontroller whose initial noise levels are different are used and
these micro-controllers are distinguished as follows. One of
them is the normal micro-controller (NMC) ad the other is low
noise micro-controller (LMC). All measurement conditions
are listed in table 1.
The measurement setup of the WBFC method is shown in
Fig. 5.
The WBFC is FC-1000 provided by TOYO
TECHNICA, and the hybrid balun is R&K HYB-3CA. The
outputted signal from the hybrid balun is amplified by
ADVANTEST R146010A and it is measured by
ADVANTEST R3131A spectrum analyzer. The power for the
EUT is supplied from the outside of the WBFC and there is a
ferrite core on the power supplying line within 300 mm from
the EUT to avoid the common-mode current flowing on the
power supplying line. The driving frequency of the microcontroller is 16 MHz, so there are strong peaks in the
measured spectra at the harmonics of 16 MHz. The measured
spectra for all conditions in table 1 at the harmonics of 16
MHz are shown in Fig. 6. Each peak of the voltage fluctuation
differs through the measurement conditions.
Next, the measurement of the common-mode current is
shown. The same setup in Fig. 1 is used for these
measurements. The current probe is ETS LINDGREN
L94111-1L and a Rhode & Schwarz FSP30 spectrum analyzer
is used. In the same way of the WBFC measurements, the
spectra of the all conditions in table 1 are shown in Fig. 7. We
see that each peak value of the common-mode currents also
differ through the measured conditions.
These measured spectra of the common-mode voltage and
current are compared and their correlation is evaluated. For
example, the compared results for 160 MHz and 288 MHz are
shown in Fig. 8. From these results, we see that each peak
value of the spectra of the common-mode voltage and current
III. MEASUREMENTS
The EUT that is used for the both measurements is shown
in Fig. 4. The size of this PCB is 110 mm × 90 mm, and it
has two conductive layers. The thickness of the PCB is 1.6
mm. This PCB is designed like a real product but there only
power and GND patterns. The rectangular marks in the Fig. 4
mean the positions where the bypass capacitors are equipped.
One of the measurement parameters is the number of the
capacitors equipped on the PCB. The other measurement
Copyright © 2009 IEICE
427
WBFC
EUT
Power Supplying
Cable
Spectrum Analyzer
Measuring
Probe
Ferrite
Core
DC cut
Filter
Hybrid
Balun
Fig. 5 An image of the measurement setup of the proposed WBFC
method.
EMC’09/Kyoto
22Q3-4
0
160 MHz
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
N.F.
40
30
20
10
0
-20
10
-30
0
-40
-10
120
170
Frequency [MHz]
220
0
-10
-20
-30
-40
220
(10)
(11)
WBFC
CISPR 25
40
-5
30
-15
20
-25
10
-35
-45
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(b)
Fig. 8 The comparison of the measured spectra of the commonmode voltage and the common-mode current for each measurement
conditions. (a) is the result of 160 MHz and (b) is that of 288 MHz.
varies similarly according to the measurement conditions.
Under 300 MHz, evaluated coefficients of correlation for the
harmonics of 16 MHz between the common-mode voltage and
current are summarized in table 2. From this table, about 76%
of the coefficients of correlation show over 0.7. Therefore
there is good correlation between the measurements of the
WBFC and the CISPR 25 methods.
IV. CONCLUSION
In this paper, a new approach to measure the commonmode voltage fluctuation on the ECU with the WBFC is
proposed. From the theoretical consideration, it is shown that
the value of the common-mode voltage fluctuation obtained
from the proposed WBFC method is proportional to the value
of the common-mode current on the wire-harness in the
CISPR 25 measurement setup. With the proposed WBFC
Coefficient of Correlation
0.9070
0.9965
0.9126
0.9871
0.5465
0.9962
-0.6014
0.5714
0.9755
0.9886
0.8662
-0.0711
0.9951
0.9201
0.8112
0.7808
0.9359
(9)
Measurement Condition
Fig. 7 The measured spectra of the common-mode current
with the CISPR 25 measurement setup at the harmonics of
16 MHz for all conditions in table 1.
Frequency
32 MHz
48 MHz
64 MHz
80 MHz
96 MHz
112 MHz
128 MHz
144 MHz
160 MHz
176 MHz
192 MHz
208 MHz
224 MHz
240 MHz
256 MHz
272 MHz
288 MHz
(8)
5
(1)
270
TABLE 2
The coefficients of the correlation for each measured frequency.
(7)
0
-50
170
Frequency [MHz]
(6)
288 MHz
Voltage Fluctuation [dBuV]
10
(5)
(a)
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
N.F.
120
(4)
50
20
70
(3)
Measurement Condition
30
20
(2)
270
Fig. 6 The measured spectra of the common-mode voltage
fluctuation with the proposed WBFC method at the harmonics
of 16 MHz for all conditions in table 1.
Voltage Fluctuation [dBuA]
-50
(1)
70
-10
20
-10
20
WBFC
CISPR 25
30
Common-mode Current [dBuA]
50
Voltage Fluctuation [dBuV]
Voltage Fluctuation [dBuV]
60
Common-mode Current [dBuA]
40
70
method, the common-mode voltage fluctuation on the
evaluation PCB is measured and its values are compared with
the measured values of the common-mode current obtained by
using CISPR 25 setup. From the comparison, it is shown that
the results obtained from these two measuring methods show
strong correlation.
ACKNOWLEDGMENTS
The authors would like to thank Dr. Ichikawa and Mr.
Mizuno with DENSO CORPORATION and Ms. Ohmae with
Production Engineering Research Laboratory, Hitachi, Ltd.
for their valuable support for this research.
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[3]
[4]
[5]
[6]
Copyright © 2009 IEICE
428
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