Know-How: what is FPD-Link III and how to test it?​

Flat Panel Display Link, better known as FPD-Link™, is a high-speed digital video interface created in 1996 by Texas Instruments – TI (formerly National Semiconductor), now used in many Automotive applications to transport video from point to point, like Navigation Systems, In-car Entertainment, and backup cameras, as well as other Advanced Driver-Assistance Systems (ADAS). The automotive environment is known to be one of the harshest for electronic equipment due to inherent extreme temperatures and electrical transients. 

FPD-Link™ III was introduced in 2010, specifically to meet automotive application requirements and to embed a bidirectional communication channel on the same differential pair, over a low-cost cable, either twisted pair or coax. This bidirectional channel transfers control signals between source and destination in addition to the clock and streaming high-definition digital video data. Therefore, FPD-Link III even further reduces cable cost by eliminating cables for control channels such as I2C and CAN bus.

FPD-Link III serializers and deserializers (SerDes) have been optimized either for the link between a processor and a display, or between the processor and a camera. Not long ago, cameras were a novel feature in an automobile, mostly used in larger vehicles to aid in seeing behind the vehicle while backing up. Today, backup cameras are included even in low-cost, sub-compact cars. As automobiles develop, there will be more and more applications for cameras in the vehicle, and the cameras will become more and more sophisticated. Furthermore, automotive vision systems industry is moving from single camera system, such as a backup camera, to multiple camera-systems.  With multiple cameras, images and synchronization becomes an important feature for next-generation systems.

In many areas, adding more capabilities to an existing technology has made the interconnects more complicated and more expensive. For example, adding copy protection to the link from your home DVD player to your video monitor requires changing from an analog coax cable to an HDMI cable. The new connection method gives better quality video, along with the copy protection. But this is at the cost of a much more expensive cable/connector ecosystem, and there is also the difficulty of supporting longer cable runs. When confronted with a similar issue within the automobile, FPD-Link III was extended to allow the same twisted-pair cable to carry copy-protected content from a Blu-ray™ player or server to a back-seat entertainment screen. In these devices, the same information that was carried over separate conductors is now encoded and carried along the FPD-Link III – sharing the same conductors that carry the video content. Getting video out of a camera and to the processor, or from a Blu-ray player to a screen, is not enough. In both cases, control signals going in the opposite direction are also required. In the case of the camera, the processor needs to configure the imager. In the case of the back-seat entertainment panel, the user interface is often a touch screen, and touch commands must be sent back from the screen to the processor. FPD-Link III handles this with an integrated return channel, which allows the same piece of coax or twisted pair to carry video in one direction, and to have an independent, bidirectional control channel sharing the same conductor. This allows the cable to remain thin, flexible and inexpensive. 

Testing of FPD-Link III displays

In automotive applications, automotive infotainment displays based on FPD-Link III chipsets, or multi-camera driver assistance systems, as well as automotive RADAR & LIDAR modules are subject to thorough V&V and manufacturing test. Testing of these devices typically includes the generation and transmission of multimedia digital stream to the corresponding receiver, and in this use case a programmable multimedia stream generator compatible with the Device Under Test (DUT) receiver is required.