SFP+ Transceiver Test: TWDPc Measurement

TWDPc, short for transmitter waveform distortion penalty for copper, takes a special algorithm defined by the SFP+ specification. This test is normally thought as a way of measuring the deterministic dispersion penalty because of a specific transmitter with regards to the emulated multimode fiber and a well- characterized receiver.

The TWDPc script (of 802.3aq, Juniper 10GBASE-LRM ) processes a PRBS9 pattern requiring at least 16 samples per unit interval. Out of concern for the large installed base of equivalent-time oscilloscopes with an archive amount of around 4000 samples, the requirement for 16 samples per unit interval was relaxed to seven samples per unit interval.

The relaxation of the necessity from 16 samples per unit interval to simply seven samples per unit interval causes worst-case pessimism of 0.24 dB TWDPc over 30 measurements. For DUTs that curently have a higher TWDPc, 0.24 dB could possibly be the difference between a pass or a fail result.

The TWDPc measurement for SFP+ host transmitter output specifications for copper requires a lot more than 70 Gsamples/s to fully capture at the least seven samples per UI. Real-period oscilloscopes offering higher sampling rates of 100 Gsamples/s or greater have a higher potential for providing accurate results for TWDPc in comparison to scopes that just offer lower sampling-rate options.

Over the board, it is necessary to map the SFP+ 10g copper signal’s data-transfer rate to the correct oscilloscope bandwidth requirements to make sure accuracy in measurement and margin testing. With a 10.3125-Gbyte/s data-transfer rate and minimum rise time of 34 ps, a scope with a bandwidth of 16 GHz or higher must meet up with the minimum requirements for SFP+. As noted, sampling rate can be an essential consideration for the TWDPc measurement.

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