A new car camera and video link for automotive applications

As the adoption of autonomous vehicles increases, the need for more automotive sensors becomes more apparent. Cameras are one of the key sensors driving the development of autonomous vehicles. The number of cameras in vehicles is increasing rapidly as new applications continue to emerge. In addition, the adoption rate of cameras continues to rise as the application of cameras moves from the lower-volume premium cars to the larger mainstream car market. Figure 1 shows the rapid growth of the automotive camera market.

Figure 1. Automotive camera market

This growth trend is expected to continue beyond 2025. In the near future, cars equipped with up to 20 cameras will become a reality.

As the number of cameras increases, the need for higher resolution also emerges. The increase in resolution is driven by two main factors. The first factor is the need to support more ADAS features, as higher resolution is required to achieve more powerful and accurate visual detection functions. The second factor is the need to display higher quality images, as consumers demand image quality from automotive cameras comparable to the high-resolution displays of smartphones.

Therein lies the problem; the lifecycle of a smartphone is significantly shorter than that of a car, so carmakers need to ensure that new models are launched with the latest display technology to keep their display systems future-proof for as long as possible.

Automotive OEMs continue to increase the size and resolution of in-vehicle displays. Therefore, displaying camera images on these larger, higher-resolution displays requires higher-resolution cameras, and using existing standard-definition (SD) cameras results in a very poor user experience (very low-resolution images). Video quality from low-resolution cameras is poor. In addition, these displays exhibit many distracting visual artifacts, such as dot patterns and color leakage - so it is no longer feasible to drive these displays with SD cameras. To provide a better customer experience, high-definition (HD) cameras are required.

Adding these cameras comes with additional costs. Not only the cost of the additional sensors and image processing, but also the cost of transmitting the video data from the camera to the processing unit through the vehicle wiring harness. The additional cables required for the camera link may not seem like a big deal, but considering that the vehicle wiring harness is the third most expensive component in the car (behind the engine and chassis), the choice of cables and connectors is critical for automotive OEMs. The wiring harness can only be designed one at a time and consumes 50% of the labor cost of the entire vehicle. The wiring harness is also the third heaviest component in the car (behind the chassis and engine). As these wiring harnesses are added to the vehicle, the vehicle production line becomes more and more problematic, and any additional production steps will further increase costs. It is also necessary to avoid adding additional weight to the vehicle, because as electric vehicles become more popular, additional weight will directly affect the vehicle's range. This problem will be further exacerbated with the introduction of many new sensors and the forecast that there will be as many as 22 billion sensors in vehicles by 2020. Any technology that can reduce the weight and cost of the wiring harness will be welcomed and very attractive to automotive OEMs.

To address this, Analog Devices has developed a new automotive camera link technology called the Car Camera and Video Bus (C²B™), which is the only technology optimized for automotive camera links and can address these issues. C²B covers three main solution-defining standards:

• Reuses existing SD unshielded twisted pair (UTP) cables and connectors to provide the simplest HD camera link upgrade.

• Use this link to transmit high-definition video with excellent picture quality.

• Use this link to meet automotive-grade EMI/EMC requirements.

Figure 2. C²B offers many benefits to camera systems

Cameras are among the highest data bandwidth sensors in the car. With the adoption of higher resolution cameras, bandwidth is further increasing. Existing SD automotive camera link solutions use low bandwidth cables, such as unshielded twisted pair and unshielded connectors. This is possible because SD cameras have lower bandwidth requirements than HD, and SD transmission standards (such as NTSC) use a multi-level transmission scheme to further reduce the bandwidth of cables and connectors. Solutions such as SERDES (also known as LVDS) require cables and connectors with much higher bandwidth than UTP, such as coaxial or shielded twisted pair (STP). This is because current SERDES solutions use non-return to zero (NRZ) signaling instead of multi-level signaling, which requires higher cable and connector bandwidth. These higher performance and bandwidth cables and connectors increase the cost and weight of the wiring harness.

C²B supports the transmission of HD resolution video over existing SD UTP cable and connector links. C²B allows for easy upgrade from SD cameras to HD cameras without changing existing cable and connector links, making it an important, cost-effective and versatile solution for OEMs.

Another advantage of reusing unshielded twisted pair is that it can use the unused pins of the existing plug-in connectors on the host and camera electronic control units (ECUs). This avoids the use of dedicated separate connectors required for SERDES technology, does not take up limited and valuable PCB space in the host and camera ECU modules, and does not increase the cost of the system solution.

C²B transmission was chosen to provide the highest robustness for this automotive application. The signaling scheme can reduce the cable bandwidth requirements by 10 times compared to other solutions. Existing links have been proven in real field applications, so there is no need to evaluate and qualify new links, which greatly simplifies the upgrade of HD cameras. In addition, because C²B technology uses an optimized transmission scheme and supports longer cable lengths (up to 30 meters), it allows OEMs to freely determine their link design and avoid some of the limitations brought by other technologies.

This C²B transmission was chosen to provide excellent video quality and EMI/EMC performance over existing cable and connector links. HD video quality is ensured over links that support lower bandwidths, especially maintaining all high-frequency video details and providing a truly outstanding video experience. Extensive video quality testing has been performed to the latest standards and the excellent video quality has been verified.

While C²B technology can support high-resolution cameras with low-cost cables and connectors, it also has its challenges. Since the link is not shielded, does not provide noise immunity, and does not directly attenuate emissions, the design of the transceiver is critical to ensure low emissions and high noise immunity to meet stringent automotive EMI/EMC requirements. From the beginning, C²B was defined and designed to meet this requirement of the automotive industry and has proven to be robust and able to meet automotive EMI/EMC requirements.

Figure 3. C²B signal chain

C²B supports many other features, including sideband control communication over the same unshielded twisted pair, enabling remote configuration of the camera module, further simplifying camera design. C²B also provides frozen frame detection, a key requirement for many OEMs.

Figure 4. C²B integrated circuit

C²B products include the ADV7990, ADV7991, ADV7380, and ADV7381, which are currently in production.

C²B provides an optimized solution that allows easy upgrade from NTSC to HD cameras using existing video links while providing excellent video quality and robust EMI/EMC performance. This exciting new technology offers many advantages and provides an optimal system solution to the increasingly complex problem of connecting multiple cameras in the car.