デンソーテクニカルレビュー Vol.10
No.２ 2005
特集 EMI Analysis of a PCB for Automotive Equipment
Using an LSI Power Current Model＊
市川浩司
鵜生高徳
宮本雅規
稲垣正史
Kouji ICHIKAWA
Takanori UNO
Masaki MIYAMOTO
Masashi INAGAKI
櫻井礼彦
Yukihiko SAKURAI
We studied an LSI’s noise source model, which is used as a power source, for noise simulation of power lines in
electronic control units in vehicles. Consequently, we have concluded that a multiple power source model is more
effective than conventional models for the power source. Next, we created an IC noise source model using the
proposed method, and tested its utility through verification of its accuracies in the VHF band.
Key words : LSI’s noise source model, EMI analysis, PCB, LSI power current model, Automotive ECU
１．INTRODUCTION
(1) Logic processing via high-speed signal carried out on a
An EMI model comprising separate models for each
single microcomputer chip placed on the PCB. The
current source within a microcomputer was used to analyze
microcomputer is the primary source of noise on a PCB.
conducted emission noise in a power circuit of a product
Therefore, measures controlling microcomputer noise
board, in order to examine the PCB power circuit system
equate to those controlling automotive ECU noise.
(elements, pattern, and circuit) in an automotive electronic
(2) PCBs for automotive ECUs use fewer layers than those
control unit (ECU) with a double-sided board. Utility of the
used in other fields as one means of controlling cost.
analysis was verified in the VHF band.
Single and double-sided boards are common, and the
ground potential for the power connection on boards is
２．BACKGROUND
unstable.
The trend toward electronic control of devices in modern
Given these characteristics, when choosing an LSI design
vehicles is advancing at a remarkable rate, as is the pace at
with low noise and considering LSI noise, the PCB design
which the capability of these devices is being improved.
issue thus becomes how to realize low cost and shorter
Thus, shorter product development cycles are required to
product development cycle times. One of the most effective
improve competitiveness. From the perspective of EMI
ways to design an automotive ECU is to define an LSI
analysis, these conditions have resulted in greater noise
noise model and simulate the circuit path and PCB noise of
propagation. Given current market conditions, however,
the design. This necessitates a model incorporating LSI
additional costs for EMI reduction cannot be justified.
noise characteristics.
Therefore, new technology enabling more efficient designs
is needed to lower EMI. To realize such new technology,
EMI performance of products must be considered from the
initial design phase. One way to accomplish this is by
analyzing noise propagation through a simulation, a method
1)
４．LSI NOISE MODEL AND METHOD OF
ANALYSIS
Many LSI noise models have been suggested
3)-9)
(Fig. 1).
The common characteristic of these models is some sort of
noise generated between the current source and ground pin,
now much in demand.
and chip, wire, and lead frame impedance components.
３．AUTOMOTIVE ECU AND
Noise results from the massive amount of device switching
CHARACTERISTICS OF GENERATED
within the LSI, which must be reproduced in the model.
NOISE
Each method of configuring these current sources has its
The primary characteristics of the automotive ECU
own set of characteristics. We reproduced these
characteristics with a current source for each frequency,
examined here are as follows.
th
＊Reprinted from“Proceedings of the 4 International Workshop on Electromagnetic Compatibility of Integrated Circuits, 2004,
Angers, France”
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特 集
Double-sided PCB
which allows the model to possess the following
Noise level (dBµV)
characteristics.
(1) The frequency range of the model is widened and the
accuracy improved because the model is built based on
the evaluation results in the frequency domain.
@80MHz
40
Board B
30
Board B
20
10
Board A
Board A
Board B
0
-10
(2) It is possible to analyze a specific frequency range
-20
using a simulation, and simulation time is reduced.
Moreover, the above characteristics are essential
Measured
Computed
Fig. 2 Analysis example using a single-current source
conditions if, when the PCB designer uses a simulation, the
problematic frequency ranges are to be quickly estimated
and the problem areas corrected.
To solve the problem point in this type of model, an LSI
model comprising separate models for each power pin,
referred to as an LSI model with separate models for each
current source, was analyzed. This model consists of the
LSI
Z2
Current
source
Power pin
current sources, which determine the amount of noise on
each power pin, as well as the internal impedance of the
Z3
LSI (Fig. 3).
GND pin
Z12
Fig. 1 LSI noise model
GND pin
Impedance
Z13
Z1
Power pin
J
Z11
The latest LSI have many power and ground pins. These
Z22
Power pin
Z23
GND pin
J1
LSIs aim to lower the impedance of the power bus on the
J2
Z21
chip and separate the power bus in order to lower its
J3
influence on peripheral circuit blocks. However, the
Z31
Z33
Z32
GND pin
Power pin
resistance of the wiring on the chip is higher than that on the
PCB, which means that variation in the power and ground
potential of the chip cannot be ignored. Additionally, power
consumption changes as performance changes; thus, it can
easily be surmised that current running through the power
Fig. 3 LSI model with multiple current sources
bus in the chip varies according to location. (This
phenomenon can be verified by measuring the magnetic
field strengths around the LSI package.)
While not shown in this figure, for the circuit in the model
Therefore, with a multi-pin power system the amount of
it is necessary to also connect each individual model
noise leakage differs by pin. In designing a PCB, taking
according to the coupling level between each of the pins. For
into account these various characteristics is particularly
the current source we configured the model such that current
effective when trying to make automotive ECUs without
was set at a specific value for each frequency analyzed.
multiple layers, as costs must be kept down. This
Using a model configured in this way mitigates loss of
necessitates the production of a simulation that makes this
precision when carrying out AC analysis in the necessary
possible. Figure 2 shows the results of modeling an LSI
frequency ranges. It also allows the necessary frequency
with a single power source with multiple power pins. We
ranges to be estimated in a short time, and makes it possible
were, however, not able to analyze the difference in the
to optimize the wiring pattern of a PCB with few layers, such
amount of noise generated in the two types of double-sided
as those used for ECUs in automobiles and elsewhere.
PCBs used.
Moreover, it can also be used by the PCB designer during the
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デンソーテクニカルレビュー Vol.10
product design process. Below are methods for producing
No.２ 2005
1000
and verifying the results of the present model, as well as
５．PRODUCTION OF THE MODEL
The specifications for the automotive single-chip
Impedance (Ω)
VCC_5A-GND_B
application examples for automotive ECUs.
100
VCC_5B-GND_C
VCC_3-GND_A
10
microcomputer modeled here.
・Operating frequency: 16MHz
1
1
・Package: QFP (80 pins)
10
100
1000
Frequency (MHz)
・Power (5V) supply pins: VCC_5A, VCC_5B
・Power (3.3V) supply pins: VCC_3
・Ground pins: 4, GND_A–GND_D
Fig. 6 Impedance between power supply pin and
ground pin
VCC_5A and GND_A are listed as current sources
The computed impedance value between ground pins
for analog circuits in their specification sheet. Also,
(GND_A, GND_C, and GND_D) in the model was found to
voltage has been stepped down for VCC_3 in the LSI.
be about 1 Ω +15 nH from measurement. In this impedance,
the inductance from the IC package can be estimated at about
The results of measuring the impedance between pins by
6 nH based on the structure (i.e., the shape and material),
network analyzer (Agilent model No. 8753ES) are shown in
which indicates that the resistance component dominates
Figs. 4 and 6.
impedance in the chip. In addition, impedance was found to
be several tens of ohms higher in (analog) GND_B than in
the other ground pins. Since as indicated impedance was
Impedance (Ω)
1000
computed high even between ground connections, the
GND_A-GND_B
GND_B-GND_C
GND_B-GND_D
100
authors analogized that GND_B and the other ground
connections were not wired into the chip. Capacitive
impedance was found between the pins when impedance in
10
the power pins was measured, indicating that the power pins
GND_A-GND_C
GND_A-GND_D
GND_C-GND_D
were not connected to each other. In addition, it was
predicted that about 200 ohms impedance would be found
1
1
10
100
1000
between VCC_5B and VCC_3 when considering direct
Frequency (MHz)
voltage run through the circuit through a 5 V to 3.3 V stepFig. 4 Impedance between ground pins
down internal regulator, and impedance between power pins
was measured via the ground side connection in the chip.
1000
From these results, in this IC it appears that the analog
circuit is, along with the power and ground pins, separate
Impedance (Ω)
VCC_3-VCC_5A
VCC_5A-VCC_5B
from the other circuits. An impedance model that
100
appropriately reflects these characteristics follows.
Next, the values for the current sources (J1, J2, and J3) of
10
the present model were estimated. To estimate these values,
the amount of current (I) flowing from the LSI was
VCC_3-VCC_5B
measured by the magnetic probe method specified in
1
1
10
100
1000
IEC61967-6. From the impedance value (Zp) of the
Frequency (MHz)
evaluation board used for measurement and from the
Fig. 5 Impedance between power supply pins
above-mentioned impedance (Z1, Z2, Z3) within the IC, the
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特 集
equivalent current for each pin was determined.
Figure 11 and Table 1 show the values calculated by
the model, as well as other evaluated results and the current
LSI
values measured at the power pins in the 3.3 V system from
I
Fig. 10.
Z2
J
Zp
Z1
10000
Z3
Z1
Calculated current (J)
Current (uA)
J=
Z1 + Z2 + Z3 + Zp
1000
Evaluation
board
I
Fig. 7 LSI’s current (I: measured, J: calculated)
100
Measured
current (I)
10
1
Figure 9 shows the impedance measured between the LSI
0.1
power and GND pins in the current evaluation board (Fig. 8)
0
160
320
480
640
800
960
Frequency (MHz)
used here (with LSI not installed). While all of the pins had
Fig. 10 Calculated current values
(J1 : for the 3.3V power system)
equivalent external impedance, the highest frequency that
could be modeled in the present evaluation board was 1 GHz
because of resonance from the pattern length of the
VCC_3
measurement board in the vicinity of 1 GHz. Consequently,
VCC_5B
VCC_5A
modeling was performed within this frequency range.
R4
C4
C1
C2
J2
J1
R1
C3
J3
R2
R3
R5
GND_A GND_D GND_C
GND_B
Fig. 11 Model structure for LSI noise model
Table 1 Model impedance
Fig. 8 Evaluation board
Impedance (Ω)
1000
VCC_3-GND_A
VCC_5A-GND_B
VCC_5B-GND_C
100
10
1
3.3V
Power system
C1=6.0 (nF)
R1=2.3 (Ω)
5.0V
Power system
C2=3.9 (nF)
R2=2.5 (Ω)
5.0V Analog
power system
C3=0.1 (nF)
R3=3.5 (Ω)
other
(R4=170 (Ω))
R5=25 (Ω)
C4=0.1 (nF)
６．VERIFICATION OF MODEL
In order to verify the accuracy of the present model, a
0.1
1
10
100
1000
10000
Frequency (MHz)
different evaluation system (evaluation board / circuit /
measurement method) was used so that the factors used
Fig. 9 Impedance in the evaluation board
during modeling would not interfere with the results. The
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デンソーテクニカルレビュー Vol.10
No.２ 2005
evaluation board and measurement method were evaluated
both analytical and measured values to again be in good
using the PCB and 1-ohm method specified in IE61967-4.
agreement. These results show that analysis with this model
The simulation values were calculated by SPICE after PCB
is fully satisfactory at the ECU product level. Figure 14
impedance was determined by the PEEC method using the
shows noise-current distribution on the PCB as an example
EMI simulator RPATH (Applied Simulation Tech, Inc.).
of the analytical results. This analysis was carried out on the
Figure 12 shows the evaluated and simulated results. A
Spice and FEM.
comparison between the present multi-current source model
and a similarly produced single-current model shows the
80
Computed
Multi-current source model
Current (dBuA)
60
-40
Noise level
at ECU connector (dBm)
values for both to be in good agreement.
Single-current source model
Measured
Computed
-60
-80
-100
-120
0
40
50
100
150
200
250
300
Frequency (MHz)
20
Fig. 13 Connector noise and current levels
Measured
0
20
70
120
170
Frequency (MHz)
Fig. 12 Verification of LSI EMC model
７．UTILITY OF EMI ANALYSIS OF AN ECU
USING THE MULTI-CURRENT SOURCE
MODEL
Next, EMI analysis in an automotive ECU using the
2.4
present multi-current source model was conducted. The
2.2
analyzed ECU was a double-sided PCB measuring 110 x
2.0
92.5 mm. The analysis was performed after selecting a +B
(battery,12-V) line for the automotive ECU and a 5-V power
1.8
dBuA/mm2
bus for the microcomputer. The reason for selecting these
was because noise generation in this ECU is concentrated in
these lines, as mentioned above. The resistance, capacitors,
Fig. 14 Results of noise-current analysis of
automotive ECU
regulator, and other elements within the range of the present
analysis were modeled under the operating voltage and
current in the target ECU. The present model was also
produced by connecting the line impedance stabilization
network specified in CISPR25 to the ECU external circuit.
８．EXAMINATION OF DESIGN METHOD
UTILIZING A SIMULATION
The utility of the present modeling method has been
presented by showing the structure and accuracy of the
The analysis results using the models was as follows
model and the results of its use in an automotive ECU.
(Fig. 13). In the ECU connector, the analytical voltage was
However, from the point of view of the ECU designer, after
-3.4 dBuV while the measured voltage was 7.3 dBuV (at 80
the CAD design is finished it is difficult and time
MHz), showing comparatively good agreement at the
consuming to make any changes found to be necessary
product board level. Moreover, the variance in impedance
when testing the design in a simulation. Thus, this is not a
with/without anti-noise devices installed on the PCB showed
practical application of the simulation in trying to meet the
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特 集
simulation will be examined in more detail in the future.
designer’s desire to promptly move into production after
the design is finished. Rather, the simulation must be used
in design or used as a tool to make a preliminary design
REFERENCES
strategy. It is from this standpoint that we examined design
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17th EMC-Noise technology symposium (Apr. 2003)
methods utilizing a simulation. As mentioned in Section 3,
the LSI is a primary source of noise in the automotive ECU,
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and LSI noise levels depend on the design of peripheral
technology in IC’s”, Union of Japanese Scientists and
circuits and PCB, as shown in Fig. 15. We have closely
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examined designs peripheral to LSIs using simulations, and
1998)
formed circuit blocks based on the results. Many ECU
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designs use the same LSI, and by developing such blocks
technology symposium (April. 2001)
an improvement in design efficiency can be effected. If the
5) Ichikawa K., “Noise reduction for LSI”, 17th EMC-Noise
accuracy of the analytical results obtained here are
compared with those in Fig. 2, an improvement can be seen
technology symposium (Apr. 2003)
but an approximately 10 dB margin of error is still present.
6) Uno T., Miyamoto M., Ichikawa K., Nakamura T.,
Therefore, in the future we will examine how to incorporate
Nakamura K., Matsui T., Mabuchi Y., Mishima A.,
simulations into the design process while also improving
Kobayashi K., Nakamura A., Hayashi T., “Analysis of a
the accuracy of the simulation results.
PCB for Automotive Equipment Using a LSI Power
Current Model”, IEICE Technical Report, EMCJ2003-
Double-sided PCB
121 ( Dec. 2003), pp.55-60.
@80MHz
20
Noise level (dB µV)
Board B
Board A
7) Uno T., Miyamoto M., Ichikawa K., Nakamura T.,
Board B
10
Nakamura K., Matsui T., Mabuchi Y., Mishima A.,
Board A
Kobayashi K., Hayashi T., Fukumoto E., “Analysis of
Board A
automobile PCBs using an LSI power source terminal
0
current model”, The 17th conference of JIEP, 12C-16
(Dec. 2003), pp.103-104.
-10
Measured
Computed
8) Mabuchi Y., Mishima A., Kobayashi K., Nakamura A.,
Fig. 15 Analysis example using the multi-current
source model
Hayashi T., Fukumoto E., Uno T., Ichikawa K.,
Nakamura K., Nakamura T., Matsui T., “EMC evaluation
technology for automobile electronics components by
９．CONCLUSION
electromagnetic field simulation”, The 17th conference of
JIEP, 12C-06 (Dec. 2003), pp.83-84.
An LSI model constructed with multiple current sources
to optimize the circuits and PCB pattern peripheral to the
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LSI was introduced. The utility of the model was made
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clear by demonstrating its accuracy.
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present model was conducted. A comparison of the
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measured and computed values for noise in the PCB
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connects showed that even when the analyzed range was
10) Yukihiro Fukumoto, Osamu Shibata, Keisuke
large, accuracy could be analyzed sufficiently at the ECU
Takayama, Tomohiro Kinoshita, Zhi Liang Wang,
product level.
Yoshitaka Toyota, Osami Wada, Ryuji Koga, “Radiated
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Emission Analysis of Power Bus Noise by Using a
examined and the effectiveness of the simulation for actual
Power Current Model of an LSI”, 2002 IEEE Int.
automotive ECUs was tested. Design methods utilizing this
Sympo. on EMC (August 2002), pp.1037-1042.
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デンソーテクニカルレビュー Vol.10
No.２ 2005
11) Ogawa M., Wafuka H., Toya H., “Descriptive method
13) International Electro-technical Commission “IEC
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(1999)
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＜著 者＞
市川 浩司
鵜生 高徳
（いちかわ こうじ）
（うのう たかのり）
統合システム開発部
統合システム開発部
EMC技術開発に従事
EMCメカニズムの研究に従事
宮本 雅規
稲垣 正史
（みやもと まさき）
（いながき まさし）
統合システム開発部
統合システム開発部
EMCシミュレーション研究に従事
工学博士
EMC設計ツール開発に従事
櫻井 礼彦
（さくらい ゆきひこ）
統合システム開発部
EMCメカニズムの研究に従事
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