Automotive Camera Interface Technology Challenges and Solutions

More and more automotive applications are being deployedCamera systems and camera interface technologies are being used to assist drivers and enhance the driving experience. Traditional rear view camera (RVC) systems equipped with only one camera are now being replaced by surround view systems (SVM) equipped with four or more cameras, which have 360° real-time vehicle monitoring capabilities. Driving recorders, blind spot monitoring, night vision, road sign recognition, lane departure monitoring, adaptive cruise control, emergency braking and low-speed collision avoidance systems can all reduce the driver's workload. To enhance the driving experience, cameras are also being introduced in a variety of applications such as driver vital signs monitoring, occupant detection and human-machine interface gesture recognition. Due to the development of camera systems, automakers can even redesign the contours of the car by replacing traditional features such as rearview mirrors.

Figure 1. Cameras are widely used in modern cars.

Many different camera applications work on the same principle as the standard definition (SD) RVC that is now deployed in many cars. For more than a decade, SD cameras have been routinely deployed in automotive applications, expanding from high-end cars to mass-market models to meet regulatory requirements and customer expectations. SD solutions offer many valuable advantages to automotive OEMs: low risk due to the maturity of the technology, which has been proven in the consumer TV industry for many years; low bandwidth requirements, which allows the use of low-cost cables andconnectors while ensuring controlled radiated performance; and a range of sophisticated video encoders and decoders that have been proven to handle unstable video inputs.

Today, ultra-high definition (UHD) displays are widely used in consumerThe rapid adoption of SD video in electronic devices is driving the need for larger, higher-definition displays in all types of vehicles. While SD video solutions may seem fine for small displays, their shortcomings become apparent when used for larger displays (e.g., lack of high-frequency detail due to limited SD video bandwidth, or cross-color artifacts when separating brightness and chrominance signals in the modulated signal). The market trend toward larger displays has challenged automotive OEMs to upgrade their camera architectures to high definition. A key building block to address this challenge is the camera interface technology that transmits the image data from the camera to the receiving unit (e.g., ECU or display).

When selecting a new camera link technology, the first application characteristic to consider is the required bandwidth. Bandwidth requirements for camera systems vary widely. Traditional RVC systems using SD video resolutions require lower bandwidth (e.g., 6 MHz). Surround view systems, which are typically used in low-speed applications, use lower refresh rates (e.g., 30 Hz) to achieve adequate exposure, which may limit the required bandwidth. Side mirror replacement systems need to operate across the vehicle's entire speed range, so higher refresh rates (e.g., 60 Hz or higher) are used to minimize latency, which requires higher bandwidth.Front cameras in autonomous driving applications require very high resolution (e.g. 18+ MPixel), so bandwidth requirements are also very high. There are many camera link technologies available that provide a wide range of bandwidths, and the choice of bandwidth range interacts with many aspects of the camera system and the entire vehicle.

Image Quality

The image quality achieved by the camera link technology is a critical factor in the architecture design. Sending video data through a camera link technology that does not provide sufficient bandwidth may compromise image integrity or cause the image to be lost entirely. Image degradation caused by the camera link technology can be assessed by measuring factors such as image sharpness and dynamic range.

Cable properties

The entire cable assembly or harness of a vehicle is one of its most complex, heaviest, and most difficult components to install. With a typical vehicle having over a kilometer of wiring, its harness requirements require careful consideration. First, applications with high bandwidth requirements (e.g., ultra-high-resolution front-facing cameras for autonomous vehicles) require the use of high-quality, heavy-duty cables. Cable weight has become a topic of increasing concern in recent years as automakers focus on making lighter and more fuel-efficient vehicles in order to increase the range of both combustion engine vehicles and electric vehicles alike. For applications involving complex routing in the vehicle, the bend radius supported by the cable can be very important. For applications where the camera is located in a hinged component (e.g., a door for an SVM system, or a trunk lid for RVC and SVM systems), the cable's robustness during opening and closing cycles is critical. For applications where the cable may be exposed to harsh environments, the cable also needs to be waterproof.

Regardless of the camera connection technology and cable type chosen, every centimeter of cable has a cost, and when all costs of the wiring harness are calculated, it can be seen that the wiring harness is one of the three most expensive components.

Due to its low bandwidth requirements, traditional SD video solutions can use lightweight and cost-effective cables. In many cases, SD video solutions use unshielded twisted pair (UTP) cables, similar to those commonly used for low-speed control links such as CAN.

Connector

Another key element of the wiring harness and the modules it connects to is the connector. In addition to connecting the harness to the control module, sensor or motor, the connector is also used to connect different parts of the same cable within the harness (in-line connectors). In-line connectors are widely used in the automotive industry to simplify the construction, installation and use of wiring harnesses. For example: using an in-line connector very close to a camera means that if the camera is damaged, it can be replaced without noticeable impact on the rest of the vehicle's wiring harness.

As with the cable selection described above, connector selection is an important determinant of the total cost of a camera system. High-resolution systems typically require connectors that support higher bandwidths and therefore cost more.

Other connector considerations include the size of the connector on the PCB and ECU, whether the connector must be sealed or unsealed, and whether color coding/keying is required.

Traditional SD video solutions allow the use of cost-effective connector solutions on the camera and ECU or multimedia host (HU). For example, the video signals of SD video RVC systems are usually connected to the ECU or HU together with other signals (such as control networks and required power signals) on a multi-pin connector; digital links usually require the use of dedicated connectors, which limits the ECU to PCB and packaging constraints.

Vehicle Architecture

Vehicle architecture has a number of impacts on the selection of the appropriate camera link technology. Cable lengths in standard vehicles can often be several meters, and as consumers begin to gravitate toward larger sport utility vehicles, cable lengths are increasing. Some vehicle architectures have additional features, such as a parking assist feature to support parking reverse and maneuvering, which may also require longer cables. Commercial vehicles present another architectural challenge. In this vehicle architecture, the camera system needs to extend the cable to the maximum length. Most camera link technologies support these vehicle architectures and features, but some may require the use of additional modules, such as repeaters or relay transmitters, to support the longer cable lengths.

EMC

The electromagnetic radiation suppression and interference immunity of the cable solution is another key factor in camera link technology, as the cable may become an antenna inside the vehicle, which may have an adverse effect. The prevalence of electronic and electrical systems in vehicles has led to an increasing reliance on these systems to coexist in a compatible manner. It is unacceptable for one system (for example: RVC system) to affect or be affected by another system (for example: electric vehicle traction motor or electric seat mechanism) when the system is activated. For this reason, its radiation and interference immunity must be considered before selecting the interface technology solution.

To ensure that internal or external interference does not affect the systems within the vehicle, automakers test all systems according to their specific EMC standards. These tests are first performed on system-level components (for example, rear-view cameras or surround-view cameras). This type of testing is costly, time-consuming, and challenging, but it ensures that each module is highly robust before integration into the vehicle. After successfully completing system-level testing, automakers must also test the system's ability to operate when continuously exposed to high-power radiated signals (radiated RF electromagnetic field immunity) to verify the operation and performance of the system in the vehicle. Manufacturers also need to measure the receive frequency bands of all antennas in the vehicle (for example, FM, GPS, mobile phone, Wi-Fi, etc.) to ensure that no interfering signals are present. Solving EMC issues in vehicles is time-consuming and costly.

other request

In addition to the above requirements, the selection of camera link technology needs to meet many other requirements, such as control channel availability, pixel accuracy and functional safety level.

summary

When designing a camera system, the choice of camera link technology is influenced by many factors. In addition, the choice of camera link technology will have many impacts on the vehicle in which it is integrated. Traditional RVC systems are based on SD video technology, which provides automotive OEMs with a very reliable and cost-effective method to achieve video transmission within the vehicle. However, consumer product trends in recent years have made SD video less and less suitable for large display sizes. At the same time, the number of cameras in each new car continues to increase due to legislative developments and consumer expectations.