FPD-Link III Cameras – Working Principle and Applications in Embedded Vision
Embedded vision is rapidly changing. The days of running minimal tasks and operations with cameras are far gone. Modern-day vision applications demand the camera to be able to transmit high-bandwidth data over long distances without compromising the quality of the image or video.
While MIPI and USB cameras have done a great job at handling heavy data, they come with serious limitations when it comes to the distance of transmission. MIPI and USB can transmit data to a distance of 30 cm and 5 meters respectively (though in USB there are variants that can go beyond 5 meters, you either have to trade off quality or bandwidth in most cases. Also, the most popular USB interfaces like USB 3.1 Gen 1 work best within 5 meters).
This is where a technique called SerDes (Serializer Deserializer) made a revolution. Of the few SerDes interfaces, FPD-Link III from Texas Instruments (TI) is one of the most popular. Though TI positions FPD-Link III primarily for automotive, in embedded vision, it can be used for a wide variety of applications including robotics, precision agriculture, autonomous vehicles, etc.
What is FPD-Link III?
FPD-Link III (Flat Panel Display Link III) is a SerDes interface that is used in embedded vision and automotive systems to transmit image and video data using a twisted pair or coaxial cable. This is how TI – the designers of FPD-Link III – defines it:
“Flat panel display link III, better known as FPD-Link III, is an interface used in many automotive applications to transport video from point to point.”
In addition to digital video, FPD-Link III can also transfer bidirectional control data and power between the processor and a sensing device or a display. The interface is capable of doing it using the same twisted pair or coaxial cable. To transmit power, FPD-Link III uses the POC (Power Over Coax) technology.
In this case, the parallel data from the host is converted into the serial mode and transmitted to the display side where the data is converted back to parallel.
FPD-Link III Cameras and Their Working Principle
As the term suggests, an FPD-Link III camera uses the FPD-Link III interface to transmit video as well as control data between a camera module and the processor.
In a camera system, the sensor or camera module is the transmitter, and the processor is the receiver. The serializer at the MIPI CSI-2 camera end converts the data into a serial stream and the deserializer on the host side converts the serial data back. FPD-Link III is a full duplex interface which essentially means that the data conversion process can happen in both directions at the same time.
The key features of FPD-Link III cameras that are key in embedded vision are:
- A maximum bandwidth of 4 Gbps and beyond (with Shielded Twisted Pair, Shielded Twisted Quad, or Coax)
- The ability to transmit video, power, and control data over the same cable.
- A maximum distance of transmission of 15m.
- Automotive grade, thereby making it suitable for most industrial and commercial applications.
FPD-Link III is an interface designed to withstand shocks and vibrations. Depending on the connector you use, the degree of ruggedness might vary. But given the interface is optimized for automotive systems, FPD-Link III cameras work well with robots, trucks, mining vehicles, and forklifts.
Camera Sensor Aggregation
Many applications require two or more embedded cameras and also require the video streams of these cameras to be analyzed by the same host processing system. Examples of these applications include surround view cameras, robotic SLAM (simultaneous localization and mapping) navigation systems, and automatic license plate recognition systems (ALPRs).
Many host processors feature a limited number of MIPI-CSI2 camera interfaces, but many support a feature called MIPI Virtual Channels (VCs). VCs allow a single MIPI-CSI2 interface to carry many independent video streams as virtual channels. The host processor captures these VCs and can operate on them as separate video streams.
The only problem with using MIPI VCs is that you need a specialized device (a MIPI-CSI2 hub) to aggregate and synchronize the MIPI-CSI2 streams from independent cameras into a single channelized MIPI-CSI2 interface to the host processor.
Typical Application Schematic (Source: Texas Instruments)
Fortunately, as part of the FPDLink III family of devices, TI offers devices like the DS90UB962, which is both a 4-channel FPDLink III deserializer and a MIPI-CSI2 hub. This means that it can transmit up to 4 independent camera video streams into the host processor over the MIPI-CSI2 interface as virtual channels. The processor can then have 4x more cameras connected to it. A processor like the TI TDA4VM SOC, which has 2 MIPI-CSI2 interfaces, can receive and operate on as many as 8 low-latency, high bandwidth camera streams simultaneously. The output interface is only limited by the maximum frequency of the deserializer’s MIPI-CSI2 interface.
The picture here shows a block diagram of camera sensor aggregation. It should have 4 cameras on the left side, facing the left. There should be a bidirectional arrow connecting each camera to a 4-input FPDLink III chip labeled DS90UB962. On the other side of the DS90UB962, there should be a MIPI-CSI2 block connecting to a generic “Host processor” block
When do You Need an FPD-Link III Camera?
To put it in one sentence, FPD-Link III cameras are required when data must be transmitted over a long distance while still maintaining the highest possible quality and the lowest latency. This can be a winner in many embedded vision applications where quick decision-making is required. FPD-Link III cameras are also suitable for industrial applications where the embedded vision system needs to withstand mechanical shocks, water intrusion, or high temperatures.
Applications of FPD-Link III Cameras
Neither MIPI nor USB interfaces were designed to support long-distance transmission. Ethernet cameras are also an option, but the interface comes with bandwidth limitations. For these reasons, embedded systems engineers have had to turn to SerDes cameras. FPD-Link III is one of the most popular SerDes camera interfaces.
A few notable applications where FPD-Link III cameras can be used include robotics, smart traffic devices, surround view systems, parking lot management systems, autonomous shopping devices, and drones.
Robotics is huge and finds application in almost every industry or domain. They are used in warehouses, retail stores, hospitals, factory floors, agricultural lands, etc. In certain robotic applications, cameras are at a distance beyond 3 meters from the host system, which makes it impossible to use USB or MIPI cameras. In such a scenario, an FPD-Link III camera can be an excellent choice – because it can transmit data up to a distance of 15m without losing any data.
Here are a few robotic applications where FPD-Link III cameras can be preferred over their alternatives:
- Large agricultural robots and tractors
- Robotic cranes and forklifts
- Telemedicine and telepresence robots
- Cleaning robots
- Companion robots
- Delivery robots
- Collaborative robots (also known as Cobots)
Smart Traffic Devices
In most cases, smart traffic devices use pole-mounted cameras to monitor traffic junctions and tolls. If the design of the smart traffic device is such that the camera is beyond 2 to 3 meters from the processor, an FPD-Link III camera is a great choice. They are excellent for capturing video data with very low latency.
Given that these devices are placed outdoors, an enclosure that can protect them from external environmental factors like water and dust would be a great addition (TechNexion’s FPD-Link III cameras come with IP68 enclosures and utilize waterproof FAKRA connectors).
Surround View Systems
Surround view systems use a minimum of 4 cameras that are mostly placed on the outside of the vehicle – whether it’s a truck, crane, construction equipment, robot, or mining vehicle. The larger the vehicle, the farther the cameras are from each other and the host processor. For example, in a trailer truck, this distance can be as long as 10 to 12 meters. This demands a long-distance interface like FPD-Link III to be used.
Parking Lot Management
Parking lot management and smart traffic devices have similar requirements when it comes to the camera. Cameras in parking lot management systems are used for ALPR (Automatic License Plate Recognition) of vehicles moving in and out of parking lots. They also help in identifying empty spots for an incoming vehicle to easily find a space to park.
Irrespective of whether it’s an open or closed parking lot, camera modules are usually mounted at a height with the processor close to the ground. To enhance visibility, the poles where cameras are mounted could very well be more than 3 to 4 meters in height. FPD-Link III cameras fit perfectly for such a use case.
Autonomous Shopping Systems
With Amazon Go and a few others redefining the way shopping is done, autonomous shopping systems have risen in popularity. They enable automated product identification and checkout with the help of cameras and computer vision algorithms. For better results, these devices use multiple cameras to capture the image of the products in the shopping cart from multiple angles or the checkout counter. Depending on the design of the cart, the cameras might or might not be placed far from the processors. FPD-Link III cameras suit well in cases where cameras are placed more than 30 cm from the host processor, and the FPD Link III hub capability allows lower-cost processors to handle multiple cameras over a single MIPI-CSI2 interface.
While many drones are small, consumer devices, many drones for commercial use are quite large. Examples include delivery drones, autonomous protection drones, firefighting drones, and drones used for military purposes.
Such drones may use multiple cameras for navigational and obstacle avoidance purposes, especially in GPS-denied environments.
Given that some cameras are placed at the apex of their arms, these drones need a vision system that can transmit data over long distances without fail. Withstanding jerks and vibrations are also key criteria to consider.
FPD-Link III cameras are suitable here, as long as you get the right combination of other features such as resolution, frame rate, lens, shutter type, and dynamic range.
FPD-Link III Cameras from TechNexion
TechNexion’s FPD-Link III cameras are compliant with the ISO 20860-1, ISO 20860-2, and USCAR 18 standards. All of them come with an IP68 enclosure making them water and dustproof.
In addition, they use the FAKRA connector – offering greater resistance to shocks and vibrations. To make implementation easy for embedded engineers, we have designed these cameras to be compatible with platforms such as NVIDIA Jetson Xavier NX, NVIDIA Orin, and the NXP i.MX8 family, TI Jacinto TDA4VM/VA/VH, and Intel/AMD (x86 systems).
Visit the FPD-Link III cameras page to go through our products.
TechNexion’s FPD-Link III cameras are compliant with the ISO 20860-1, ISO 20860-2, and USCAR 18 standards. All of them come with an IP68 enclosure making them water and dustproof. In addition, they use the FAKRA connector – offering greater resistance to shocks and vibrations. To make implementation easy for embedded engineers, we have designed these cameras to be compatible with platforms such as NVIDIA Jetson Xavier NX, NVIDIA Orin, and the NXP i.MX8 family, TI Jacinto TDA4VM/VA/VH, and Intel/AMD (x86 systems).
Visit the FPD-Link III cameras page to go through our products.
As we discussed, FPD-Link III cameras are best suited for applications that need reliable long-distance transmission with good transfer rates. So, every embedded vision system doesn’t need them. Given that they are more expensive than MIPI or USB cameras, you need to be wise with your choice.
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