I have seen so many debates around the technical merits of CoaXPress and Camera Link HS that I sometimes feel we may have overlooked what I would say is nearly as important – when a product is reliable and performs adequately for its purpose, the next important criterion for consideration must be cost.
I was recently discussing the new camera interfaces and their impact with my lead frame grabber designer. Our discussion quickly moved to the BOM cost. (BOM stands for Bill of Materials and represents the total cost of the components used to manufacture the product – that is, before the profit margin that any for-profit company would apply before selling it to you). Market pressure constantly forces us all to minimize BOM costs and this is no different with CoaXPress or Camera Link HS frame grabbers. This is where the unique implementation aspects of these 2 technologies diverge.
CoaXPress is based on a breakthrough technology from EqcoLogic: an asymmetrical transceiver chip offering bidirectional transfer over a coaxial cable. This enables 6.25 Gbps per port from camera to frame grabber and an uplink of 21 Mbps for camera control. Obviously an extremely attractive solution since one can bundle a small number of coax cables to scale the transmission bandwidth. But there is a hidden cost to that: the integrated transceiver is only available from EqcoLogic with low volume pricing of $38 according to their news release. For a typical four port CoaXPress frame grabber, this represents $152 directly added to the BOM cost. And you can easily figure out the camera will also need four of these chips, increasing the total system cost by the same amount! As a point of reference, the National Semiconductor chip used by Camera Link has a budgetary price of $5.25 and three such chips are required to support Camera Link FULL: fora total less than $16. You obviously don’t get the same transmission performance: CoaXPress gets you to 2500 MB/s (after 8B/10B encoding) versus the 850 MB/s of Camera Link FULL 10-tap. But a 3-fold bandwidth increase for a 9-fold cost increase! Really?? Not a typical ratio for technology where performance is expected to increase with a decline in price. Even assuming volume pricing for the CoaXPress transceiver, it is hard to turn such a ratio around.
This is where my friendly frame grabber designer reminded me of the cost advantage of Camera Link HS, the other camera interface to offer more than 2 GB/s of transfer bandwidth. Gone is the expensive single source transceiver chip. It is simply replaced by the SERDES (serializer/deserializer) integrated in today’s mainstream FPGAs augmented by appropriate buffers (about $20 added to the BOM). This brings the overall frame grabber BOM cost down by $130, and keeps my product manager happy :-). A win-win situation for me. And for you as a system integrator if product cost is your topmost criterion!
Till next time!