C2B: A New Car Camera Link for Automotive Applications
By Fionn Hurley, Analog Devices, Inc.
Introduction
As autonomous vehicles become more prevalent, the demand for automotive sensors, particularly cameras, is rapidly increasing. Camera applications are expanding from premium vehicles to standard vehicle markets, driving growth in the automotive camera market.
Figure 1 illustrates the automotive camera market's rapid growth, showing projected unit growth from 2015 to 2025. The market is expected to continue its upward trend beyond 2025, with vehicles potentially supporting up to 20 cameras.
This growth is accompanied by a need for higher camera resolutions, driven by the requirements of Advanced Driver-Assistance Systems (ADAS) and consumer demand for high-quality visual displays comparable to smartphones. Automobile manufacturers must ensure their display systems remain relevant throughout a vehicle's lifespan, which is significantly longer than that of a smartphone.
Original equipment manufacturers (OEMs) are increasing display size and resolution, necessitating higher resolution cameras. Standard definition (SD) cameras provide a poor user experience on these displays, exhibiting artifacts like dot crawl and color leakage. High definition (HD) cameras are therefore required for a better customer experience.
The integration of more cameras increases costs, not only for sensors and image processing but also for data transfer via copper wiring in the vehicle harness. The wiring harness is a significant cost and weight factor in a car. With the increasing number of sensors and the drive towards electric vehicles (where weight impacts range), reducing cable harness weight and cost is crucial for OEMs.
To address these challenges, Analog Devices, Inc. (ADI) developed Car Camera Bus (C2B™), a technology optimized for car camera links. C2B offers three key advantages:
- • Offering the easiest upgrade path to HD by reusing existing SD unshielded twisted pair (UTP) cable and connector infrastructure.
- • Supporting high definition video with excellent visual quality using this infrastructure.
- • Meeting all automotive EMI/EMC requirements using this infrastructure.
Technical Details and Advantages
Figure 2 outlines the advantages of C2B for camera systems. It highlights the use of lightweight, unshielded twisted pair cables and cost-effective sideband communication for HD cameras and ECUs. Key features include frozen frame detection, extensive video/cable diagnostics (up to 30 meters), and superior cable compensation performance.
Cameras are high-bandwidth sensors. Existing SD camera link solutions utilize lower-bandwidth infrastructures like unshielded twisted pair (UTP) cables and connectors, which support SD transmission standards like NTSC using multilevel signaling. In contrast, solutions like SERDES (LVDS) require higher-bandwidth cables such as coaxial or shielded twisted pair (STP) due to non-return to zero (NRZ) signaling. These higher-performance cables increase cost and weight.
C2B enables HD video transmission over existing SD UTP cable and connector infrastructure by employing multilevel signaling to reduce bandwidth requirements. This provides a cost-effective and resourceful solution for OEMs, allowing an easy upgrade from SD to HD cameras without changing the existing infrastructure.
An additional benefit of reusing UTP cabling is its compatibility with free pins on multipurpose block connectors in head units and camera ECUs, avoiding the need for dedicated connectors required by SERDES technologies, thus saving space and cost.
The C2B transmission format was chosen for its robustness in automotive applications. Its signaling scheme reduces cable bandwidth requirements by 10x compared to other solutions. Reusing existing infrastructure simplifies HD camera upgrades, as the infrastructure is already field-proven. C2B technology also supports longer cable lengths (up to 30 meters), offering OEMs flexibility in infrastructure design.
The data format for C2B transmission was selected for excellent video quality and superior EMI/EMC performance. HD video quality is maintained over lower-bandwidth infrastructure, preserving high-frequency visual detail for an excellent video experience, verified by extensive testing.
While multilevel signaling allows for high-resolution cameras over low-cost cables, it presents challenges. The lack of shielding in UTP requires critical transceiver design for low emissions and high immunity to meet stringent automotive EMI/EMC requirements. C2B was designed from the outset for the automotive industry, proving robust for these requirements.
Figure 3 illustrates the C2B signal chain. It shows data flow from a camera module, including an Image Sensor, ISP, and C2B TX, to a Camera ECU containing a C2B RX and SOC. Various channels are depicted: Video Channel (Downstream), Control Channel, GPIO (Upstream/Downstream), I2C (Bidirectional), Interrupt (Downstream), and Status (Downstream).
Additional Features and Products
C2B supports additional features like sideband control communication over the UTP cable, enabling remote configuration of camera modules and simplifying camera design. It also includes frozen frame detection, a key requirement for many OEMs.
Figure 4 showcases C2B integrated circuits, including Analog Devices' ADV7990, ADV7991, ADV7380, and ADV7381, which are currently in production.
C2B offers an optimized solution for upgrading from NTSC to HD cameras using existing infrastructure, delivering excellent video quality and robust EMI/EMC performance. This technology provides numerous advantages, enabling an optimal system solution to address the growing need for connecting multiple cameras within a vehicle.
References
- 1 "Automotive Ethernet: An Overview." Ixia, May 2014.
About the Author
Fionn Hurley is marketing manager with the Automotive Cabin Electronics Group at Analog Devices, Inc. (Limerick, Ireland). Fionn joined Analog Devices in 2007, previously working as an RF design engineer. He holds a bachelor's degree in electrical and electronic engineering from University College Cork, Ireland. He can be reached at fionn.hurley@analog.com.
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