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: email@example.com Mr. Michael Rucks Michael.firstname.lastname@example.org 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) All rights reserved. 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