How to use SFP Connectors in Your PCB Layout

SFP connectors are used to route data into fiber optic transceiver modules, which are normally found in high-pace networking gear. Today, nonetheless, I’ve had multiple design requests that involve using fiber transceivers exterior of a knowledge middle setting. Newer systems in sensor fusion, MIMO methods, rugged OpenVPX switches, and a few industrial robotics need to stream large amounts of data again to a workstation or server, with data streams easily exceeding 10 Gbps per lane. Streaming this a lot data from a small embedded gadget calls for either a fiber transceiver or a bundled mini coax interconnect. The latter remains to be a bulky connector over copper, so I’m not shocked that engineers are requesting an SFP kind factor for production grade techniques. As I count on to see more of this going into the long run, I decided to arrange this brief information on the correct usage of SFP connectors and transceiver modules that concentrate on these very excessive information charges. The small type issue pluggable (SFP) connector is designed to connect directly to modules that interface with copper or fiber.

These are generally used with fiber hyperlinks in the information middle, although these links at the moment are being discovered elsewhere as I mentioned above. The connector is designed to offer a hot-swappable interface for transceiver modules just like the Cisco 10G module proven beneath. The module features a set of contacts alongside the edge that plug into the SFP connector, and the SFP connector will mount to the PCB as an ordinary SMD part. SFP modules designed for one type of connector should not suitable with another type of connector. Note, nevertheless, that in case your connector vendor is out of inventory, different connectors might be substituted into the PCB header connector. Within the format example I’ll show under, I’m utilizing an ordinary 20-pin SFP connector for a 25G hyperlink over fiber (as much as a hundred m length). The same technique can be used with the opposite types of SFP connectors with increased pin counts listed above, in addition to QSFP connectors for 4-channel modules.

The important points in the structure are as follows: High-density PCB connector on the right, we’ve got an I2C interface and a few control alerts. All of these are low pace and may usually be routed away from the high-speed differential pairs coming to the left aspect of the connector. In case you loved this short article and you would like to receive more information concerning High-speed PCB connector please visit the internet site. Copper pour was used for balancing in this explicit board, however this is not a requirement for the transceiver to operate correctly. Next, the excessive-velocity indicators enter from the left side, and they’re surrounded by GND and PWR pins. These lines are passing into the inside layers using differential vias, the vias drop down to L6 in an 8-layer PCB. Because the outer two dielectrics are thin (11 mil complete thickness), the stub size is already minimized on this via transition and backdrilling shouldn’t be wanted. The differential pairs cross through an optimized antipad that units the required differential impedance to 100 Ohms up to a bandwidth of approximately 10 GHz.

At very fast data charges, where multiple lanes are aggregated right into a single QSFP connector, the connector physique itself might grow to be apparent as the main issue limiting knowledge charge. Connector manufacturers have made efforts to qualify their elements in opposition to goal information rates, but of course these data price targets may not be hit totally when the traces on the PCB are routed into the connector. A transmission line simulation program like Ads or Simbeor could be wanted to fully qualify these channels when interfacing with a QSFP connector. It’s necessary to remember, optical transceivers are sending out fast pulses into an optical fiber, so that they operate identical to every other excessive-speed digital part. This means we have to fret about energy integrity on the facility bus for these connectors. The everyday tips for prime-pace digital PDN design apply to SFP connectors as well. Within the above instance, the incoming energy is passed through a low-go filter based on test information from our companion on the above project.

Watch out with this method as inserting pi filters on a energy pin for a excessive-speed part may end up in excitation of a really robust transient if the filter just isn’t critically damped. So until you may prove the filter works, consider just utilizing extra capacitance to suppress rail noise. The pictures above just present an SFP connector mounted on to the PCB as a simple connector. The optical transceiver module would then connect to the board alongside its edge, and the transceiver would present through the enclosure. This is fine if the enclosure has some technique to fix the module into the enclosure in order that the module is stable. The connector proven above could also be moved again away from the sting of the board in order that fiber interface is closer to the board edge, as could be the case the place the enclosure has a tight fit to the board edge. In many pieces of networking tools, the SFP connector won’t often grasp off the sting in this fashion.