Automotive serializer deserializer SerDes: to achieve a better ADAS camera

Whether it is a mobile phone or an ultra-high-definition TV screen, the high dynamic range image (HDR) camera is no longer limited to providing popular visual effects. More and more high-performance cameras support advanced driver assistance systems (ADAS) and autonomous vehicle (AV) applications. Take Waymo as an example. At least 29 cameras are installed on its fifth-generation self-driving car, in addition to 5 lidars and 6 radars.

Whether it is a mobile phone or an ultra-high-definition TV screen, the high dynamic range image (HDR) camera is no longer limited to providing popular visual effects. More and more high-performance cameras support advanced driver assistance systems (ADAS) and autonomous vehicle (AV) applications. Take Waymo as an example. At least 29 cameras are installed on its fifth-generation self-driving car, in addition to 5 lidars and 6 radars.

Future self-driving cars will need to support a total bandwidth of 3 to 40 GBit/s (approximately 1.4 to 19 TB/h), of which the camera generates the most data.

Automotive serializer deserializer SerDes: to achieve a better ADAS camera
Figure 1: Among ADAS and AV sensors, the camera generates the largest amount of data per second. Data source: Lucid Motors

In-vehicle network-sub-domain architecture

These different types of sensors use different data rates in the bottom plate. One of the challenges facing automotive engineers is how to reduce the complexity of the in-car network through a domain-specific architecture.

Automotive serializer deserializer SerDes: to achieve a better ADAS camera
Figure 2: Conceptual diagram of domain-based in-vehicle network architecture

Figure 2 is a simplified Display of the partition architecture: different types of sensors are aggregated into different partitions, and the automotive Ethernet serves as the interconnection between the partitions or domains.

The role of automobile SerDes is becoming more and more important

ADAS’s camera sensors require high data rates and transmission speeds to operate as designed. Developers are increasingly turning to serializer/deserializer (SerDes) connections to connect these cameras to the vehicle’s image processing Electronic control unit (ECU), as shown in the light orange interconnection in Figure 2. This SerDes connection converts parallel data to serial data (and vice versa), enabling faster communication between devices using lower-cost cables and connectors.

Currently, SerDes solutions are delivered by vendors using closed proprietary standards, but this situation is about to change. The industry recognizes that transparent and unified standards and test requirements will prompt chip suppliers, automotive Tier 1 suppliers, and automakers to speed up development cycles, reduce costs, and improve interoperability with other commercial equipment.

The industry is already solving some of the urgent challenges that SerDes faces in terms of vehicle networking, such as verifying:

• Interoperability between different media related interface (MDI) cables and connectors
• Integrity of transmitter, interconnect and receiver performance
• The robustness of the system to various electromagnetic interference (EMI)
• Network security from the physical layer to the entire protocol stack

Interoperability is a real problem. Transceivers are sensitive devices and must be carefully tested to ensure they can work in severe automotive environments, including high temperature, vibration, electrostatic discharge, and electromagnetic interference. Let’s look at some examples of transceiver testing.

Transmitter test

As far as the transmitter is concerned, it is necessary to ensure that the characteristics of the transmitted signal are good.

Automotive serializer deserializer SerDes: to achieve a better ADAS camera
Figure 3: Rear-view ADAS security camera with packet loss

Figure 3 is an example of a car reversing camera view with horizontal lines. These lines are packet loss caused by transmission gaps. The driver may still be able to see the image with a few missing data packets, but if a child suddenly appears behind the reversing vehicle and the transmission flashes black, it will be catastrophic!

There are multiple suppliers involved in the realization of this safety function: camera manufacturers, cable suppliers, and switch suppliers that send signals, as well as GPUs or ECUs that process data, and brakes that are ultimately used to park. We can see why overall interoperability is crucial.

Channel test

Link or channel testing is essential to ensure the signal integrity between the transmitter and receiver. In view of the cable length used in the harsh automotive environment, looking at the relationship between impedance and frequency is also an important part of predicting the channel’s performance in the car.

The link part includes cables and inline connectors, as well as matching connectors at both ends. Ultimately, the wiring harness is responsible for transmitting control and payload data, as well as providing DC power for remote sensors.

The channel characteristics of the SerDes link include time domain and frequency domain analysis. This requires looking at the wiring system, media-related interface (MDI), and fixture and test setup requirements.

Automotive serializer deserializer SerDes: to achieve a better ADAS camera
Figure 4: Example of a media-related interface (MDI) connector with H-MTD and SMA

The actual MDI connector is not standard, but there are some strict specifications to help ensure that unnecessary interaction between the MDI and the cable is minimized. For example, Figure 4 provides an example of an H-MTD connector for multi-Gig automotive Ethernet, which can also be used for the emerging SerDes standard.

In the channel test, we need to find errors, such as:

• Impedance mismatch
• Signal distortion or defect
• Crosstalk between cables

Receiver test

The receiver is responsible for understanding the data sent through the link and then passing it to the ECU or Display device for further processing. Errors in the receiver will result in the loss or damage of data from safety-critical sensors such as cameras, radars, and lidars.

A veritable receiver function becomes increasingly difficult, especially when transmitting over a long channel exposed to multiple simultaneous noise sources. To describe the capabilities of the receiver, the error level in the presence of multiple noise sources must be measured, including:

•Narrowband interference
•High current injection
• Instant transient
• Crosstalk of alien cable bundles

The measurement device can include noise sources, amplifiers, and coupling circuits, which lead to precise levels of noise into the active SerDes link. Then query the signal quality register of the device under test (DUT) to verify that the receiver can correctly interpret the signal in the presence of noise. The focus of receiver testing is to put pressure on the receiver to ensure that it can still maintain the bit error rate.

In-car network testing becomes critical

According to MarketsandMarkets data, the global automotive camera and integrated radar and camera market is expected to grow from US$6.1 billion in 2021 to US$10.1 billion in 2026.

Due to the need for more cameras and other sensors to ensure higher safety and promote autonomous driving, in-vehicle network testing has become a non-negligible link. Only by ensuring interoperability and meeting the performance standards of its mission-critical functions can it be better promoted Autopilot.

The Links:   LM150X08-TL04 G104V1-T01

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