2014-01-0249
Published 04/01/2014
Copyright © 2014 SAE International
doi:10.4271/2014-01-0249
saepcelec.saejournals.org
Technical Issues of 100Mbit/s Ethernet Transmission based
on Standard Automotive Wiring Components
Reinhard Felgenhauer and Michael Rucks
Delphi Automotive
ABSTRACT
The presentation describes a technical solution for 100 Mbit/s Ethernet Data transmission cabling. This solution considers
the specific requirements of automotive wiring harness and manufacturing. It bases on standard automotive connectors
and headers.
Currently the development of automotive electronic architecture considers central ECU or data backbone structure for the
upcoming EE architecture (e. g. single ECU for network; SEN). For these structures solid and cost effective data backbone
solutions are essential.
Ethernet, a wide distributed and well-known bus system for office and industry data distribution provide a wide range of
software tools and many physical layer solutions. Several cabling systems are available. Based on this we propose a
solution for automotive application.
CITATION: Felgenhauer, R. and Rucks, M., "Technical Issues of 100Mbit/s Ethernet Transmission based on Standard
Automotive Wiring Components," SAE Int. J. Passeng. Cars – Electron. Electr. Syst. 7(2):2014, doi:10.4271/2014-01-0249.
INTRODUCTION
Several car manufacturers are planning to use data backbone
architectures. All these solutions provide a high speed data
backbone for the upcoming data distribution requirements.
Ethernet is a candidate to enter automotive technology. The
reasons from data transmission software position are obvious.
Automotive industry is on its way to autonomous driving and
the demand of data transmission is rising continuously.
Automotive industry expects to reduce hard and software
development cost due to the synergy with office, industrial and
avionic Ethernet applications. This close relationship with other
Ethernet installations, promise cost reduction and additional
safety aspects for automotive use.
Scalability, a feature of Ethernet, is an additional aspect for
future data transmissions and an essential reason for this
technology.
100 Mbit/s is the current standard for data transmission. A
bitrate of 1Gbit/s is scheduled as a future extension step.
PHYSICAL LAYER FOR ETHERNET IN
AUTOMOBILE
The challenge is, to provide a physical layer (cable, connector,
inline), which fulfill the technical requirements for such a
transmission media combined by low cost and technical
robustness.
The manufacturing of such devices should be possible in the
current chain of automobile wiring harness production.
Special cable and connector with dedicated termination
processes will increase the cost of the transmission media.
This investigation fulfills the technical requirements and base
on standard automotive terminals and automotive connectors
to achieve cost reduction.
An electronic company provides a transmission system chip
set for unshielded twisted pair (UTP) cables as transmission
media. This chipset is designed for a symmetric twisted pair.
Felgenhauer et al / SAE Int. J. Passeng. Cars – Electron. Electr. Syst. / Volume 7, Issue 2 (August 2014)
The technical requirements for twisted pairs are unusual for
automotive wiring harness suppliers. Due to this, the single
wire of the harness becomes an electronic device with new and
specific features.
The transfer functions and other transmission parameters of the
data channel in frequency area are in focus of investigation.
Data channel is a synonym for all the passive devices of the
data transmission link.
The high speed data stream has to be transmitted with low
losses; low reflections and without electromagnetic interference
with other electronic devices inside and outside the automobile.
The electromagnetic interferences are reduced by a symmetric
cable and connector design. Shielding and transmission
requirements will be achieved by a dedicated termination
process.
A suitable way to describe the behavior of the channel in
frequency range is using S-Parameters.
DATA TRANSMISSION
The electronic transmission is calculated by the data
transmission theory. (Fourier transformation) This mathematical
theory based on the transfer calculation from time functions
into functions in the frequency area. For each electrical signal,
a transformed function in the frequency area can be calculated.
The transfer-function of the transmission system is specified in
frequency parameters. Based on this an output signal is
calculated.
S-PARAMETERS
The relevant S-Parameters for transmission behavior are: S21 is
the insertion loss (IL) and S11 the return loss (RL) or reflection.
The insertion loss describes the attenuation of a signal in
respect to the frequency level.
The return loss indicates the reflection of a signal in the
transmission channel in respect to their frequency.
A specific feature of this kind of twisted pair transmission
technique is the conversion mode.
The differential signal on the twisted wires is transferred into a
common signal on both wires by asymmetry mechanical and
electrical properties. This effect is tested by the S-Parameters
“Transverse Conversation Loss” (TCL) and “Equal Level
Transverse Conversation Mode” (ELTCTL)
DATA CABLE TRANSMISSION
REQUIREMENTS
We considered coated and uncoated twisted pair cable with
2× 0.35 mm2 (AWG 22) with an impedance of (100 ± 5) Ω.
Coated cables have better impedance stability than uncoated
designs.
Figure 1. path of mathematical calculation
After this, the function is recalculated into the time function.
(see: Figure.1)
PVC cables have high attenuation and a worst temperature
stability of the data transmission parameters. The reason is the
bipolar characteristics of the insulation material PVC.
This is the basics of the data transmission calculation. Several
parameters in this frequency parameter area are defined to
verify the technical features of data transmission channel.
(see: Figure.2)
The well-known PVC isolation material is not suitable for data
cable, because PVC has a significant change at its relative
permittivity (Ɛr) in the automotive temperature range of −40 …
+105°C.
(Change from 2 … 6).
PVC cables do not meet the impedance requirement of (100 ±
5) Ω in the specified temperature range.
PP or similar materials are appropriate for isolation materials.
Figure 2. Electrical Transmission System
Due to this, the focus of interest changes from time range to
frequency range.
Felgenhauer et al / SAE Int. J. Passeng. Cars – Electron. Electr. Syst. / Volume 7, Issue 2 (August 2014)
CONNECTOR TRANSMISSION
REQUIREMENTS
The conventional automotive connectors design for 0,64mm
terminals provide, more or less by accident, sufficient
impedance characteristics. The connector array meets the
requirements for data transmission and reflection.
Investigations in detail show room for improvements on header
side. Figure 3 shows the impedance range along the
transmission path.
A constant value of impedance along the transmission path
indicates good results in transmission (insertion loss) and
return loss.
Figure 5. Assembly area without IMP
The impedance could be matched by re-twisting of wires, or
putting “something” around the wires to hold the wires close
together.
We call this “something” impedance matching part (IMP).
An investigation of several solutions of impedance matching
devices has shown several positive solutions.
One solution does also meet the requirements of
manufacturability of automotive wiring harness production.
(see: Figure 6)
Figure 3. Impedance Measurement
Figure 6. Assembly area with IMP
DATA TRANSMISSION SYSTEM
REQUIREMENTS
Figure 4. Connector/Header/Cable Combination
DATA CABLE ASSEMBLY REQUIREMENTS
A challenge is the assembly of coated twisted pair cable to the
terminals and the assembly of the terminated cable ends into
the connector cavities. This process is usually a manual
process.
For this, the cable is unjacketed and untwisted on a length of
50 mm.
The terminals are crimped onto the individual wires. After this
the single terminals are locked into the cavities of the
connector body.
The 50mm open wire end has unacceptable impedance values
and significant effects in case of shielding, emission and data
transmission.
This data transmission, based on one single unshielded twisted
pair, is in focus due to low cost installation cost, small volume
and low manufacturing expenses. The manufacturing cost
could be reduced by well-known automotive standard terminals
and connectors.
The focus of this investigation was, to check this standard
connector for the 100 Mbit/s data transmission applications.
The insertion loss and the return loss test result demonstrate
the quality and stability of the proposed solution. (see: Figure 7
& 8)
Investigation of termination technique achieves a robust
termination process for twisted pair wires which meets the
requirements of the 100 Mbit/s Open Alliance Specification.
The impedance matching part is an essential device to meet
these specifications.
Delphi could achieve a solution within its wiring harness
manufacturing capabilities and could demonstrate the technical
accomplishments.
Felgenhauer et al / SAE Int. J. Passeng. Cars – Electron. Electr. Syst. / Volume 7, Issue 2 (August 2014)
CROSS TALK AND SHIELDING
REQUIREMENTS
The shielding and cross talk parameters of these cabling
solutions are specified by the S-Parameters “Near end Cross
Talk” (NEXT), “Power-Sum Near End Cross Talk” (PS-NEXT),
“Attenuation to Cross talk Ratio at Near End” (ACR-N) and
“Power Sum Attenuation to Cross talk Ratio at Near End”
(PS-ACR-N).
These parameters define the different cross talk features of the
data transmission channel.
Figure 7. Insertion Loss
These parameters are defined on system level. We have
tested the proposed twisted pair solution according these
limits. For this, we twisted a jacketed twisted pair sample (PESDK 0030) to a round cable be using the symmetrical structure
1+6. (see: Figure 11)
Figure 8. Return Loss
The test results of TCL and ELTCTL, (see in Figure 9 & 10),
demonstrate this achievement in signal mode conversation.
Figure 11. Setup for Cross Talk Testing
For this structure we could present results for the cross talk
testing (see: Figure 12).
The test procedure is not defined finally. Due to this, these
results are first hints for the quality of the proposed solution.
Figure 9. Scd11 TCL
Figure 12. Cross Talk Measurement
IMPLEMENTATION OF DATA WIRES INTO
WIRING HARNESS
Figure 10. Scd21 ELTCTL
These new parameters for cables and connectors create new
challenges for automotive wire and harness suppliers. The
cable for data transmission becomes an electronic device with
electronic requirements (S-Parameter).
Felgenhauer et al / SAE Int. J. Passeng. Cars – Electron. Electr. Syst. / Volume 7, Issue 2 (August 2014)
Data transmission requires more technical features than the
simple electrical connectivity which require resistance and
insulation properties for automotive wires.
Ongoing investigation will focus on cost saving and optimized
manufacturing and improved quality. A quality check has to be
defined for mass production.
We could demonstrate an engineering solution for 100 Mbit/s
single twisted pair data transmission. This engineering solution
has to be transferred into production.
One possible improvement is the wire size reduction down to
0.13 mm2 (AWG 26).
The implementation of data links into the wiring harness and in
the automotive environment may create additional challenges.
The current status is a jacketed twisted pair copper cable with
a wire size of 0.35 mm2 (AWG 22)/(see: Figure 13)
The upcoming technology step is the connector size reduction
down to 0.50mm pins associated with the connector body size
reduction.
This cable design gives also room for improvement. We expect
smaller wires, smaller terminals and improved twisted pair
technologies. The connector design could improve the data
transmission features.
REFERENCES
Figure 13. Cable
We use the connector size of 0.64mm pin size. These pins are
plugged into standard connector housing. The pinning in the
connector housing has to consider special requirements in
respect to the cross talk limits. This item is content of ongoing
investigations. (see: Figure 14)
Schwab A. J.; Kürner W.; Elektromagnetische Verträglichkeit, 6.
Auflage; Springer Verlag
Simony K.; Theoretische Elektrotechnik; 7.Auflage; VEB Deutscher
Verlag der Wissenschaft Berlin 1979
Wikipedia; Fourier-Transformation
Wikipedia; Fourier-Analysis
Wikipedia; Laplace-Transformation
Definition for Communication Channel; Open Alliance, Oct. 2013
CONTACT INFORMATION
Mr. Reinhard Felgenhauer:
reinhard.felgenhauer@delphi.com
Mr. Michael Rucks
Michael.rucks@delphi.com
ABBREVIATIONS
ECU - Electronic Control Unit
Figure 14. Connector
A spiral tube achieve for the impedance matching (IMP). This
device is mounted around the wires of the twisted pair at the
unjacketed area, after the two data wires are plugged into the
connector cavities. (see: Figure 15)
EU - Europe
EE architecture - Electric/Electronic Architecture
IMP - Impedance Matching Part
IL - Insertion Loss
RL - Return Loss or reflection
TCL - Transverse Conversation Loss
ELTCTL - Equal Level Transverse Conversation Mode
NEXT - Near end Cross Talk
PS-NEXT - Power-Sum - Near End Cross Talk
PES-DK 0030 - Internal numbering system for data cable
samples (here: No: 0030, Flexray Cable)
Figure 15. Assembled Cable with IMP
FUTURE OUTLOOK
The future application will increase the bitrate up to 1GBit/s.
Associated with this are increased requirements for all
technical S-Parameters. Some of them are not finally fixed.
ACR-N - Attenuation to Cross talk Ratio at Near End
PS-ACR-N - Power Sum Attenuation to Cross talk Ratio at
Near End
AWG - American Wire Gauge
Felgenhauer et al / SAE Int. J. Passeng. Cars – Electron. Electr. Syst. / Volume 7, Issue 2 (August 2014)
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