1770 - LatticeECP3: Are there any special considerations to interface the LatticeECP3 SERDES to standard SFP transceiver modules?
Referring to the Small Form-factor Pluggable (SFP) Transceiver MultiSource Agreement (MSA), the LatticeECP3 SERDES inputs and outputs are compatible with the specification. This allows for a very clean interface between the module and the fpga.
The RD-/+ are the differential receiver outputs of the SFP module. They are AC coupled 100 Ω differential lines which should be terminated with 100 Ω (differential) at the user SERDES. The LatticeECP3 receivers include the appropriate on-chip termination. The on-chip 50-ohm input terminations should be used in the Lattice CML input.
AC coupling is done inside the SFP module thus not required on the FPGA SERDES host board. However the Lattice CML input architecture will require the on-chip ac-coupling be enabled. The voltage swing from these differential outputs will be between 370 and 2000 mV differential (185 – 1000 mV single ended) when properly terminated. The LatticeECP3 allows a maximum input swing should not exceed 1760mV single ended into the CML input pins. Therefore the SFP output is within the allowable range of the LatticeECP3 CML input.
TD-/+ are the differential transmitter inputs of the SFP module. They are AC-coupled, differential lines with 100Ω differential termination inside the module. The AC coupling is done inside the module and not required on the FPGA host board. The inputs will accept differential swings of 500 – 2400 mV (250 – 1200 mV single-ended. The LatticeECP3 provided programmable output characteristics that match this requirement without the need for any on-board terminations. The Lattice CML output should use the programmable 50-ohm pullup resistors to VCCOB.
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