How do car camera bus and FPD Link compare?

Car camera bus (C2B) and flat panel display (FPD) Link are both technologies used in automotive vision systems, but they differ in their use cases, performance, and cost. Automotive high-definition link (AHL) is another choice for video connectivity, as is automotive Ethernet, a general-purpose networking technology.

This article briefly compares FPD Link, C2B, and AHL.

FPD-Link is an open standard that can be used without a license. It was originally developed by National Semiconductor, which Texas Instruments acquired. FPD-Link IV, the latest version, is a high-speed serializer/deserializer (SerDes) that enables high-bandwidth video transfer and audio support in vehicles.

FPD-Link IV can drive multiple displays from a single serializer device, with each deserializer connected by a coax cable. It can support high-bandwidth automotive processors for displays up to 8K UHD resolutions. Its high bandwidth and low latency make it suitable for surround-view camera systems, LiDAR, radar, etc.

Some cameras in advanced driver assistance systems (ADAS) must be synchronized so frames captured by different cameras can be aligned in time. Hardware triggers or software synchronization through FPD-Link IV can achieve this.

FPD Link uses coax cables that can carry 13 gigabits per second (Gbps) of data and control signals and enable video bandwidth of more than 25 Gbps over two cables. FPD-Link IV technology also supports daisy chaining and splitting to drive multiple displays with one SoC interface (Figure 1).

Figure 1. FPD Link can support the infotainment and ADAS systems. (Image: *Texas Instruments*)

Where does C2B fit?

C2B was designed by Analog Devices to provide HD performance at a low cost by using an unshielded twisted pair (UTP) cable instead of a more expensive coax. Typical applications include automotive ADAS, surveillance cameras on buses, and general-purpose video transfers. One focus of C2B is the use of existing low-cost UTP cabling to upgrade from standard-definition cameras to HD without changing the wiring.

The combination of multilevel signaling, internal filtering, and optimized video encoding delivers immunity to electromagnetic interference and reliable performance. It also includes a high-speed backchannel for remote camera control. The signaling results in an order-of-magnitude reduction in cable bandwidth requirements, enabling UTP cabling.

Figure 2. Connectivity and exemplary features of a C2B implementation. (Image: *Analog Devices*)

What about the AHL?

Like C2B, AHL is designed to transport HD video over UTP cabling. Both are used for similar applications. Renesas Electronics developed AHL and uses efficient video compression algorithms to transmit high-quality video data over the lower-bandwidth cable while minimizing latency.

The ability to send control signals to the camera simultaneously over the same UTP cable that carries the video data boosts the performance of an AHL system and keeps costs low. The always-available control channel operates independently from the video stream and can be used to initialize camera settings at start-up and send I2C, GPIO, and interrupt commands to the camera during active video transmission (Figure 3).

Figure 3. Simplified representation of an AHL signal highlighting the I2C control channel. (Image: *Renesas Electronics*)

Summary

FPD Link, C2B, and AHL are all viable options for automotive vision systems, but they differ in their use cases, performance, and cost. To determine the best choice for a specific application, designers need to weigh the tradeoffs between latency, control signals, image quality, wiring simplicity, the ability to support daisy chaining and splitting, and other factors.