TECH | FOCUS
Compact Devices Temper Noise in
Electric Cars
T
he trend towards computerization in the car market has been
growing in recent years. It is
expected that the number of
electronic devices incorporated in one
car will rise due to the increasing use of
electric cars and fuel cell cars and enhancements in additional functions, such
as advanced driver assistance system
(ADAS), while the types of electronic
devices will diversify.
Computerization of cars requires incar local area network (LAN) in order to
enable their in-car electronic devices to
exchange information with each other.
In-car LAN needs to be fast enough to
transmit a large amount of information,
and to be highly reliable in terms of
communication quality; therefore, many
interfaces designed for in-car use are
adopted. One of the most widely used
forms of in-car LAN is Controller Area
Network (CAN). CAN is a so-called differential interface with a bit rate of up to
1Mbps and can connect many
Currents identical in phase
nodes to one bus through bus
connection, thereby making it
possible to build a one-to-many communication network.
Because of its high reliability,
CAN is used in a wide range of
applications from car navigation systems to engine control.
In recent years, also, in-car
Currents opposite in phase
Ethernet has been developed
Figure 1: Basic structure of a common mode choke coil in order to allow high-speed
Table 1: Exterior and main characteristics of the DLW43SH Series
Murata PN
DLW43SH110XK2 DLW43SH220XK2
Length
4.5mm
Width
3.2mm
3.2mm
Thickness
2.6mm
2.6mm
Case Size (inch)
4.5mm
1812
1812
360mA
310mA
Insulation Resistance (min.)
10M ohm
10M ohm
DC Resistance (max.)
0.5 ohm
0.6 ohm
11μH +50/-30%
(at 100kHz)
22μH +50/-30%
(at 100kHz)
Rated Current
Common Mode Inductance
Operating Temperature
Range
-40 to +125 degC -40 to +125 degC
transmission of a large amount of information, such as video signals in response
to the increasing use of in-car cameras,
among others. In-car Ethernet is based
on the conventional Ethernet technology used for consumer equipment, and
is a differential interface that is capable
of high-speed communication as fast
as 100Mbps, like 100Base-TX and the
like for consumer use. One of the in-car
Ethernet technologies is BroadR-Reach,
which was established by the standards organization OPEN Alliance SIG.
BroadR-Reach uses a single unshielded twisted pair (UTP) cable to allow
100Mbps bidirectional transmission, and
is expected to be widely used particularly
for in-car camera applications.
Noise Problems with In-Car Devices
An in-car LAN needs to have high reliability in communication quality because
its communication failure could result in
the loss of human lives; the reliability is
particularly affected by so-called electromagnetic noise. In order to solve electromagnetic noise problems, it is necessary
to prevent the occurrence of noise that
can affect wireless communication used
within a car and to ensure high noise resistance so as to protect communication
quality against noise coming from the
surroundings. CAN and in-car Ethernet
apply differential transmission as a communication method to alleviate these
electromagnetic noise problems. Specifically, in differential
transmission, signals
transmitted by
DLW43SH510XK2 DLW43SH101XK2 are
passing currents op4.5mm
4.5mm
posite in phase along
3.2mm
3.2mm
a pair of transmission
2.6mm
2.6mm
routes, so that the mag1812
1812
netic fields around the
230mA
200mA
routes are in the op10M ohm
10M ohm
posite direction and so
1.0 ohm
2.0 ohm
negate each other, pre51μH +50/-30% 100μH +50/-30%
(at 1MHz)
(at 1MHz)
venting the occurrence
of
electromagnetic
-40 to +125 degC -40 to +125 degC
noise in the surroundAEI February 2015
Copyright©2015 Dempa Publications, Inc.
39
TECH | FOCUS
Murata PN
DLW32SH110VK2 DLW32SH220VK2 DLW32SH510VK2 DLW32SH101VK2
The exterior and
main
characterWidth
2.5mm
2.5mm
2.5mm
2.5mm
istics of the DLThickness
2.3mm
2.3mm
2.3mm
2.3mm
W32SH Series are
Case Size (inch)
1210
1210
1210
1210
shown in Table 2.
Rated Current
240mA
200mA
170mA
150mA
The DLW32SH SeInsulation Resistance (min.)
10M ohm
10M ohm
10M ohm
10M ohm
ries has a reduced
DC Resistance (max.)
0.75 ohm
1.0 ohm
1.7 ohm
2.0 ohm
size of 3.2 × 2.5 ×
11μH +50/-30%
22μH +50/-30%
51μH +50/-30%
100μH +50/-30%
Common Mode Inductance
(at 100kHz)
(at 100kHz)
(at 100kHz)
(at 100kHz)
2.3mm while offerOperating Temperature
ing equivalent per-55 to +150 degC -55 to 150 degC
-55 to 150 degC
-55 to 150 degC
Range
formance. Also it
Table 2: Exterior and main characteristics of the DLW32SH Series
has surface mount
metal terminals as
Murata PN
DLW43MH201XK2
have high environa structural feature, which reduces the
Length
4.5mm
mental durability.
influence of thermal expansion and conWidth
3.2mm
traction due to temperature change. As
Thickness
2.6mm
Noise
a result, it has an operating temperature
Case Size (inch)
1812
Suppression
range of -55 to +150ºC.
Rated Current
110mA
Components
Murata Manufacturing is also developInsulated Resistance (min)
10M ohm
Typically, coming the DLW43MH Series as common
DC Resistance (max)
4.0 ohm
mon mode choke
mode choke coils for in-car Ethernet.
Common Mode Inductance typ.200uH (at 100kHz)
coils are used as
The exterior and main characteristics of
noise
suppresthis product are shown in Table 3. DeTable 3: Exterior and main characteristics of the DLW43MH Series
sion components
spite having the same size as the DLing area. Also in differential transmission,
for differential interfaces such as CAN
W43SH Series, 4.5 × 3.2 × 2.6mm, the
noise coming from the surroundings is
and in-car Ethernet. The basic structure
DLW43MH Series has an improved comunlikely to cause communication failures
of a common mode choke coil consists
mon mode inductance of 200μH, allowbecause typically such noise has the same
of two coils wrapped around one maging noise suppression over a wide bandphase and so is unlikely to interfere with
netic core, as shown in Figure 1. When
width. In addition, its special winding
differential transmission signals.
currents opposite in phase flow through
structure allows it to provide improved
these two coils, the magnetic fields
However, even in differential transcharacteristics for modal transformation
around the magnetic core are in the opmission, it is impossible to completely
and more effective noise suppression.
posite direction, and so negate each othsolve noise problems and there are sever; in contrast, when currents identical in
eral factors that can lead to noise. The
Testing of Noise Suppression Effects
phase flow, the magnetic fields are in the
factors include (1) unbalance in output
In order to test the effects of noise
signals, (2) unbalance in substrate wiring
same direction and so high impedance is
suppression by the DLW43SH and
or cables, and (3) combination of noise
obtained. This effect allows the common
DLW32SH Series in a CAN, a CAN evalfrom other circuits in the device. The first
mode choke coil to transmit differential
uation board was used to carry out noise
factor is a case in which signals from a
measurement. For noise measurement, an
signals opposite in phase and suppress
communication IC are not ideal differanechoic chamber of Murata Manufacturcommon mode noise identical in phase.
ential signals and include signal compoing was used and peak detection measureMurata Manufacturing Co., Ltd. has
nents identical in phase, which will be
ment was carried out in a measurement
commercialized the DLW43SH Series as
radiated as noises. The second factor is
environment conforming to CISPR 25, an
noise suppression components for CAN.
emission standard for in-car devices. On
a case in which signals opposite in phase
The exterior and main characteristics
the evaluation board, 250kHz pulse sigare translated into signals identical in
of this series are shown in Table 1. The
nals were input into a TXD terminal for
phase because there is an unbalance in
DLW43SH Series is a set of noise suppresa CAN transceiver, and then CAN sigthe length of substrate wiring or impedsion common mode choke coils for in-car
nals were output and transmitted through
ance. The third factor is a case in which
LAN such as CAN and FlexRay, which
a cable; under the circumstances, noise
noise from other circuits in the device is
are surface-mount components with a size
was measured. The common mode choke
mixed after it is transmitted inside a subof 4.5 × 3.2 × 2.6 mm. It has a common
coils used were DLW43SH510XK2 and
strate or is radiated within the device.
mode inductance of up to 100μH and
DLW32SH510VK2. The measurement
As described above, even in an in-car
a cutoff frequency of about 1000MHz,
results are shown in Figure 2. Figure 2
LAN that applies differential transmiscompatible with high-speed differential
shows that harmonic noise based on a fresion, noise may occur for various reasons,
signals. Due to its operating temperatures
quency of 250kHz, equivalent to the sigand so it is necessary to deal with noise
of -40 to +125ºC, it can be used in a wide
nal frequency, occurred, but it also shows
using noise suppression components.
range of in-car applications.
that the use of common mode choke coils
Noise suppression components used in an
Moreover, the DLW32SH Series is
was able to reduce any noise by up to
in-car LAN need to be compatible with
presently being developed as a miniaturthe in-car environment, and so need to
20dB or so.
ized version of the DLW43SH Series.
Length
40
AEI February 2015
Copyright©2015 Dempa Publications, Inc.
3.2mm
3.2mm
3.2mm
3.2mm
Horizontal
70
No filters
50
40
30
20
No filters
60
DLW43SH510XK2
Noise Level (dBuV/m)
Noise Level (dBuV/m)
60
Vertical
70
10
DLW43SH510XK2
50
40
30
20
10
0
0
㻜㻚㻝
㻝
㻝㻜
㻝㻜㻜
㻝㻜㻜㻜
㻜㻚㻝
㻝
Frequency(MHz)
Horizontal
70
No filters
㻝㻜㻜㻜
No filters
60
DLW32SH510VK2
Noise Level (dBuV/m)
Noise Level (dBuV/m)
㻝㻜㻜
Vertical
70
60
㻝㻜
Frequency(MHz)
50
40
30
20
10
DLW32SH510VK2
50
40
30
20
10
0
0
㻜㻚㻝
㻝
㻝㻜
㻝㻜㻜
㻝㻜㻜㻜
㻜㻚㻝
㻝
Frequency(MHz)
㻝㻜
㻝㻜㻜
㻝㻜㻜㻜
Frequency(MHz)
Figure 2: Effects of noise suppression by the DLW43SH and DLW32SH Series in CAN
Figure 3: Effects of noise suppression by the DLW43MH Series in in-car Ethernet
Next, the results of the evaluation of
noise suppression for in-car Ethernet
are shown. A communication evaluation
board compatible with in-car Ethernet
was used to measure noise radiated during
inter-board communication. A measurement environment conforming to CISPR
25 in the same way as the above environment for CAN was used. The common
mode choke coils used were DLW43MH201XK2. The measurement results are
shown in Figure 3. Figure 3 shows that
when common mode choke coils were
not used, noise occurred at 66MHz and its
harmonic noise also occurred, but it also
shows that the use of DLW43MH201XK2
eliminated noise peaks, reducing noise
over a wide frequency band.
Conclusion
In order to describe Murata Manufacturing’s noise suppression products aimed
at the in-car device market, this document
focuses on the DLW43SH, DLW32SH,
and DLW43MH common mode choke
coil series, along with noise suppression
examples, for CAN and in-car Ethernet.
Murata Manufacturing will contribute to
solving noise problems in the car market where computerization is underway,
by continuing to improve such products
aimed at the in-car device market.
About This Article:
The author, Yasushi Saito, is from the
Application Development Sec., Product
Development Dept. 2, EMI Filter Division, Murata Manufacturing Co., Ltd.
AEI February 2015
Copyright©2015 Dempa Publications, Inc.
41