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More about the Samtec FireFly multi-Gbps optical interconnect system for high-speed backplanes in FPGA-based systems

Xilinx Employee
Xilinx Employee
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Yesterday, I wrote a blog post that included information on the Samtec FireFly Micro Flyover System for high-speed, multi-Gbps backplane communications. This system is used for optical backplane interconnect in the Pentek Flexor 5973 3U OpenVPX FMC carrier board. (See “Pentek OpenVPX board points the way to multi-Gbps optical backplanes using VITA 66.4 optical interconnect.”) Samtec just sent me some additional information on the company’s FireFly system and the material merits a full blog post of its own because it answers a real system-design question: How do I want to use all of those multi-Gbps SerDes links in Xilinx FPGAs?


Here’s a more detailed photo of Pentek’s answer to that question:



 Pentek Flexor 5973 3U OpenVPX FMC Carrier Photo.jpg


Pentek Flexor 5973 3U OpenVPX FMC Carrier Board


You can see the separate 12-channel Samtec ECUO FireFly Tx and Rx Active Optical Micro Flyover Cable Assemblies in the center of the above image—they’re capped with finned aluminum heat sinks and they’re plugged into Samtec UEC5 FireFly card sockets. You can also see 12-fiber multicolor ribbon cables exiting each FireFly optical assembly, running over the top of the board’s Xilinx Virtex-7 FPGA, and terminating in the VITA 66.4 dual 12x MT optical connector, which forms part of the board’s VPX backplane connector array. Each ECUO Tx and Rx channel can reportedly handle 14Gbps. The Xilinx Virtex-7 GTH SerDes channels directly driving the Samtec optical assemblies are rated for maximum operating rates of 13.1Gbps, but I have seen them overclocked to 14.06Gbps. (See “3rd-Generation Bandwidth Engine from MoSys (Bigger, Better, Faster) needs sixteen 28Gbps lanes to strut its stuff.”)


One of the very cool aspects of the Samtec Firefly interconnect design is that the optical modules plug into the Pentek board using special connectors that accept high-speed ECUE copper-interconnect cables as an alternative to the ECUO optical assemblies. The choice between optical and copper interconnect gives system designers interesting alternatives. If I am reading the Samtec ECUE technical note properly, the FireFly ECUE copper interconnect will support 14Gbps operation for channel lengths of 23 to 30 inches and 28Gbps operation for channel lengths of 8 to 15.5 inches. Perhaps that’s not long enough for a backplane-based system but it’s plenty long enough for a direct board-to-board connection.


Here’s a 3-minute Samtec video illustrating the FireFly concept:




FireFly™ Micro Flyover System from Samtec



The GTH SerDes ports on the Virtex-7 VX330T and VX690T FPGAs used on the Pentek Flexor 5973 3U OpenVPX FMC carrier board top out at 13.1Gbps but Xilinx does offer 28Gbps GTZ SerDes transceivers on the Virtex-7 H580T and H870T 3D FPGAs. In addition, you can get 32.75Gbps GTY SerDes transceivers in the new Xilinx 20nm Virtex UltraScale FPGAs and 16Gbps SerDes transceivers in the new 20nm Kintex UltraScale FPGAs.


You’ll find more information on the Samtec FireFly ultra-high-bandwidth interconnect system here.