The explosion of Ethernet in-vehicle nodes, and the test of multiple buses side by side faces four challenges

Comparing the cars of the past, present, and future, there is a clear trend: cars have become data centers on wheels. Inside every car, the flow of data from safety systems, onboard sensors, navigation systems, and more, and the reliance on that data, is growing rapidly. In the next few years, we expect to see more than 100 ECUs in every car, with connected in-vehicle networks carrying several terabytes of data per day.


Comparing the cars of the past, present, and future, there is a clear trend: cars have become data centers on wheels. Inside every car, the flow of data from safety systems, onboard sensors, navigation systems, and more, and the reliance on that data, is growing rapidly. In the next few years, we expect to see more than 100 ECUs in every car, with connected in-vehicle networks carrying several terabytes of data per day.

Figure 1. The increasing number of sensors and ECUs requires faster data rates and wider bandwidths

As sensors grow in number and sensitivity, they generate enormous amounts of data. It is conceivable that 10~20 cameras provide a 360-degree panoramic view, and all cameras send 1080p (now) or 4K (in the future) HD data streams, and the pixel depth is increased from 16-bit to 20-bit or even 24-bit. The numbers are quickly adding up: a 4K camera that supports 24-bit pixel depth produces 199 Mb of data per frame at 10-30 frames per second. While 1 Gbps rates may be sufficient now, 10Gbps will soon be required.

Currently, IVNs employ preprocessing hardware to perform data reduction on the sensor. Unfortunately, this affects response time, while also degrading image quality, limiting the available detection distance. An emerging solution is to deliver raw data at 2 – 8 Gbps to centralized system-on-chips (SoCs) or general-purpose processing units (GPUs), which can compress incoming real-time data. IVNs are moving from a flat structure to a domain controller structure, where sensors send raw data to a central processing unit.

As speeds reach 10 Gbps, Automotive Ethernet will play an increasing role in carrying high-speed data communications, including:

• IEEE 802.3cg, 10BASE-T1, 10 Mbps;
• IEEE 802.3bw, 100BASE-T1, 100 Mbps;
• IEEE 802.3bp, 1000BASE-T1, 1 Gbps;
• IEEE 802.3ch, 10GBASE-T1, 2.5/5/10 Gbps.

Given the increasing data rates available and the demand for these capabilities, along with the need to reduce cable weight, many industry observers are optimistic about the growth of automotive Ethernet and the number of connected in-vehicle nodes.

The concept of Automotive Ethernet was proposed by the OPEN Alliance SIG, also known as IEEE 802.3bw (formerly BroadR-Reach), an Ethernet physical layer standard designed for automotive networking applications, such as advanced safety features, comfort and infotainment features . With Automotive Ethernet, multiple in-vehicle systems can access information simultaneously over a single unshielded single-pair cable. For automakers, the technology reduces networking costs and cable weight while increasing signal bandwidth.

To achieve higher signal bandwidth, automotive Ethernet uses a full-duplex communication link over twisted-pair cables, supporting simultaneous transceiver functions and PAM3 signaling. Full duplex communication with PAM3 can complicate viewing of automotive Ethernet traffic and signal integrity testing.

The OPEN Alliance develops automotive Ethernet test specifications for components, channels, and interoperability. The test system incorporates an Electronic control unit (ECU), connectors and untwisted pair cables. The test requires the system to work under the harsh environmental and noise conditions inside the vehicle. To do this, users must be able to characterize and view signal integrity and traffic at the system level in order to perform reliability testing.

Examples of applications where customers require signal integrity testing at the system level include:

• TC8 Signal Quality Test
• ECU component characterization and testing
• Characterization and testing of automotive Ethernet cables, connectors, cable lengths and routing
• Electromagnetic noise or Gaussian noise testing
• High current injection test
• Production unit tests
• Impact of Automotive Systems on Automotive Ethernet Performance – DC Motor On/Off – Engine On/Off
• Automotive Ethernet system debugging

It is recommended to perform signal integrity testing during the design phase to identify potential problems before system integration.

Figure 2. Automotive Ethernet full-duplex communication chain

Challenge: Test multiple buses side by side

Testing in-vehicle networks requires reliability checks throughout the vehicle, including interoperability, immunity to interference, crosstalk, and sources of interference. Verification of operational functionality and communication reliability will cover a bus-connected system managed by each ECU inside the car (below). As vehicles become increasingly data-intensive, testing becomes critical to ensure safe and reliable operation at all stages of the lifecycle, including development, validation, production, maintenance and servicing.

Figure 3. Example of in-vehicle network structure

Test Challenge #1: Debug Bus Issues

In-vehicle communications can still be affected by noise, circuit board routing, and startup/shutdown timing, resulting in problems such as excessive bus errors and lockups. Multiple buses running simultaneously in the enclosed space of an automobile can generate EMI, resulting in poor signal quality. Pre-compliance testing can help you isolate and identify the cause of signal quality issues and bus performance issues, plus improve your ability to pass formal EMI and Electromagnetic Compatibility (EMC) testing against relevant standards such as CISPR 12, CISPR 25, EN 55013 , EN 55022 (replaced by EN 55032) and CFR Title 47, Part 15.

Test Challenge #2: Verify Electrical Conformance

Ensuring reliable low-latency data flow between and within vehicles is critical to the safe operation of the entire system. Automotive Ethernet has a complex set of compliance tests specified by the IEEE and the OPEN consortium, including various electrical requirements, to ensure compliance with the standard. These tests are typically performed during design, verification, and production. In automotive Ethernet, physical (PHY) layer electrical testing covers several key metrics of transmitter/receiver (transceiver) performance, as shown in the table below. The specific goal of these measurements is to test the consistency of the physical media attachment (PMA) against various electrical parameter data.

Figure 4. 100/1000BASE-T1 Electrical Test List

Test Challenge #3: Verify Protocol Compliance and System Performance

Automotive Ethernet uses a technology called tri-level PAM or PAM3 to achieve higher data rates at the same clock frequency. In PAM3, each level must operate within a specific voltage and relatively tight tolerances. These signals can be quite complex, but oscilloscope-based eye-diagram measurements can be a useful way to visually determine signal performance relative to signal encoding requirements (i.e. protocol testing). The key metrics for an eye diagram are eye height, eye width, linearity, and thickness (below). Taken together, these metrics provide practical information on how accurately and reliably the signal can provide encoded information.

Figure 5. Cumulative eye diagrams provide an efficient way to view and characterize multilevel signals over one or more cycles

It’s also worth pointing out that Automotive Ethernet operates at full duplex, so the two linked devices can send and receive data at the same time. This provides three related advantages over traditional shared networks: first, two devices can send and receive data at once instead of taking turns sending and receiving data; second, the overall bandwidth of the system is greater; third, full duplex can Implement multiple sessions simultaneously between different pairs of devices such as master and slave. In addition to these complexities, automotive engineers face another challenge: using PAM3 signaling for full-duplex communication makes it difficult to view automotive Ethernet traffic before fully characterizing signal integrity. To perform signal integrity analysis on a link and decode the protocol in a real system environment (using an oscilloscope), the designer must view each link separately, which requires signal isolation before analysis can be performed.

Figure 6. The actual vehicle Ethernet signal, the master and slave signals cannot be separated

Reliable communication between nodes is critical to vehicle operation. Because of this, we strongly recommend testing signal integrity and protocol at the system level under a variety of environmental conditions, including varying cable lengths, injected noise, and more.

Test Challenge #4: Get the information you need to troubleshoot and debug

Whether the issue is bus performance, EMI, electrical conformance, or protocol conformance, there are two fundamental metrics that determine signal quality and, in turn, data performance, amplitude and timing. The accurate operation of these two indicators is essential to ensure the successful transmission of digital information through the bus. This is also becoming more and more difficult due to faster bus speeds and more complex signal modulation techniques (such as PAM3). When starting to debug, there are six common problems, the root causes of which are usually well known:

• Amplitude issues: ringing, dip, runt
• Edge Distortion: Board routing problems, improper termination, circuit problems
• Reflections: Board routing issues, improper termination
• Crosstalk: Signal coupling, EMI
• Ground bounce: Excessive current draw, internal resistance of power and ground loops
• Jitter: noise, crosstalk, timing instability

Oscilloscopes are the measurement tool of choice, but without adequate frequency coverage, channel count, accessories, and on-screen analysis capabilities, troubleshooting and debugging can become tedious and time-consuming.

Tektronix Automotive Ethernet Solutions

Standardized Conformance Testing

Tektronix is ​​committed to leading-edge standards work and conformance testing for in-vehicle networking. Actively participate in and provide industry-leading solutions in standard organizations such as IEEE, Open Alliance, HD-BASE Alliance and MIPI A-PHY. The following table provides a conformance test cheat sheet:

Table 1 Automotive Ethernet Conformance Test Cheat Sheet

System-Level Signal Integrity: See the Real Signal

There are two ways to separate automotive Ethernet master and slave signals over a single twisted pair:

1. Directional coupler method

The user is required to disconnect or cut the automotive Ethernet cable and insert a directional coupler to separate and test the signal. This approach is inherently flawed in achieving accurate testing with minimal disturbance. Cutting cables at the system level is not an easy task, so this method is not suitable for system level testing. With this method, the user can view the master and slave signals, but it introduces insertion and return loss, making it difficult to determine whether the error is caused by the system or by adding hardware. Also, while we may be able to remove the effects of directional couplers, de-embedding may amplify noise in the system, affecting measurement and characterization accuracy.

Until recently, the directional coupler method was the default test method for automotive Ethernet because Tektronix’ software-based signal separation test method was not available.

Figure 7. Automotive Ethernet Directional Coupler Signal Separation Method

Figure 8. Automotive Ethernet Tektronix Signal Separation Method

2. Tektronix Signal Separation Method

The Tektronix Signal Separation method, introduced in July 2019, separates full-duplex signals by viewing voltage and current waveforms from both the master and slave test points, and uses a proprietary software algorithm to provide the separated signal. The Tektronix Signal Separation Method is a software-based solution that allows the user to see the real signal without cutting the automotive Ethernet cable. One of the advantages of this method is that it can Display the master and slave signals without the added insertion and return loss and de-embedding effects of the directional coupler method.

Figure 9. Comparison of Two Signal Separation Methods for Automotive Ethernet

As shown in the figure above, in the actual signal example, if the Tektronix signal separation method is used, since the actual connection and the embedded directional coupler are not destroyed, the peak-to-peak value of the obtained PAM3 signal is about 2V, which is relative to the embedded directional coupler. At 200mV peak-to-peak, the PAM3 eye diagram obtained by the Tektronix signal separation method has a much higher amplitude and a better signal-to-noise ratio. With this new approach to automotive Ethernet testing, users can characterize signals with greater accuracy and in less time without the added expense and measurement challenges. Users can use this method to perform signal integrity testing at the system level, performing all the tests available in the application environment.

Figure 10. Flexible PAM3 Signal Separation and Protocol Decoding

At the same time, Tektronix oscilloscope also provides comprehensive advanced analysis functions of in-vehicle Ethernet PAM3 signals and bus protocol decoding functions. You can refer to the following table to find the required solution:

Tektronix and its solution partners have created a unified approach to in-vehicle network testing. Across all major IVNs and throughout the vehicle lifecycle, we can help you and your team bring new designs to production faster, accelerate validation testing, enhance compliance testing, optimize production testing, and simplify service and post-repair testing. The end result, can greatly enhance your ability to meet costs and timelines.

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