How to make use of SFP Connectors in Your PCB Layout
SFP connectors are used to route information into fiber optic transceiver modules, which are usually found in excessive-pace networking equipment. Today, however, I’ve had multiple design requests that contain using fiber transceivers outside of an information center surroundings. Newer methods in sensor fusion, MIMO methods, rugged OpenVPX switches, and a few industrial robotics need to stream big quantities of data again to a workstation or server, with knowledge streams easily exceeding 10 Gbps per lane. Streaming this a lot knowledge from a small embedded machine calls for either a fiber transceiver or a bundled mini coax interconnect. In case you loved this information and you want to receive details with regards to High-density SMT PCB connector connector (related web-site) kindly visit our web site. The latter remains to be a bulky connector High-density PCB connector over copper, so I’m not stunned that engineers are requesting an SFP kind factor for manufacturing grade techniques. As I anticipate to see extra of this going into the longer term, I determined to prepare this temporary guide on the correct usage of SFP connectors and transceiver modules that target these very high information charges. The small type factor pluggable (SFP) connector is designed to connect directly to modules that interface with copper or fiber.
These are generally used with fiber links in the information heart, although these links are actually being found elsewhere as I mentioned above. The connector is designed to provide a hot-swappable interface for transceiver modules just like the Cisco 10G module proven under. The module features a set of contacts alongside the sting that plug into the SFP connector, and the SFP connector will mount to the PCB as a standard SMD component. SFP modules designed for one type of connector aren’t suitable with one other type of connector. Note, nevertheless, that in case your connector vendor is out of inventory, other connectors will be substituted into the PCB. In the format instance I’ll present below, I’m utilizing a normal 20-pin SFP connector for a 25G hyperlink over fiber (up to 100 m size). The same strategy can be used with the other sorts of SFP connectors with higher pin counts listed above, in addition to QSFP connectors for 4-channel modules.
The essential factors within the format are as follows: on the proper, we have an I2C interface and some control indicators. All of those are low velocity and should generally be routed away from the excessive-pace differential pairs coming to the left aspect of the connector. Copper pour was used for balancing in this explicit board, but this is not a requirement for the transceiver to perform properly. Next, the high-velocity alerts enter from the left facet, and they’re surrounded by GND and PWR pins. These strains are passing into the inner layers utilizing differential vias, the vias drop right down to L6 in an 8-layer PCB. Because the outer two dielectrics are skinny (eleven mil whole thickness), the stub size is already minimized on this via transition and backdrilling just isn’t needed. The differential pairs pass via an optimized antipad that units the required differential impedance to 100 Ohms up to a bandwidth of approximately 10 GHz.
At very fast knowledge rates, the place multiple lanes are aggregated into a single QSFP connector, the connector physique itself could change into obvious as the principle issue limiting knowledge fee. Connector manufacturers have made efforts to qualify their elements against target knowledge charges, however in fact these knowledge charge targets may not be hit absolutely when the lines on the PCB are routed into the connector. A transmission line simulation program like Ads or Simbeor can be needed to completely qualify these channels when interfacing with a QSFP connector. It’s essential to remember, optical transceivers are sending out fast pulses into an optical fiber, in order that they perform similar to another excessive-velocity digital component. This means we’ve to worry about power integrity on the facility bus for these connectors. The everyday guidelines for prime-pace digital PDN design apply to SFP connectors as well. In the above instance, the incoming power is handed by means of a low-pass filter based on test information from our companion on the above challenge.
Be careful with this approach as inserting pi filters on a energy pin for a high-pace element can result in excitation of a really strong transient if the filter will not be critically damped. So unless you can show the filter works, consider just utilizing more capacitance to suppress rail noise. The pictures above just show an SFP connector mounted directly to the PCB as a simple connector. The optical transceiver module would then hook up with the board along its edge, and the transceiver would show via the enclosure. This is fine if the enclosure has some method to repair the module into the enclosure so that the module is stable. The connector proven above could also be moved back away from the edge of the board in order that fiber interface is closer to the board edge, as would be the case where the enclosure has a tight match to the board edge. In lots of pieces of networking gear, the SFP connector won’t usually dangle off the edge in this manner.
