Some Challenge And Testing Of SFP+ Transceivers Compatible Cisco SFP+

SFP+ is the upgraded version of the SFP, 10G SFP+ transceiver are multi-purpose optical modules for 10Gbit/s data transmission applications at 850nm, 1310nm and 1550nm. The transceivers are ideally suited for datacom and storage area network (SAN/NAS) applications based on the IEEE 802.3ae and Fibre Channel standards, Fiber Channel 10G, 8.5G, 4.25G, 2.125G, 1.0625G, 10GB SFP+ SR/SW/LR/ER, 1000 Base-SX Ethernet. The 10G SFP+ transceivers are fully compliant to the SFP+ MSA and are hot-swap.

While Cisco SFP+ helps to reduce overall system cost, it puts new burdens on the PHY’s design and performance. The SFI between the host board and the SFP+ module presents significant design and test challenges.

One obvious challenge is the increased port density and the testing time required with 48 or more ports per rack. For instance, there are 15 measurements each for the host transmitter tests, and each of those measurements using manual methods can easily take from three to five minutes. This means a test engineer will take more than an hour per port to complete the required tests, multiplied across the number of ports.

Another challenge is moving seamlessly from a compliance environment to a debug environment. If a measurement fails, how can the designer determine which component is causing the failure and debug the issue to arrive at the root cause? Such determinations are especially challenging given the tight physical packaging and compact designs.

Yet another problem that most designers face today relates to connectivity: how to get the signal out from the device under test (DUT) to an oscilloscope. Test fixtures are typically required but questions arise around whether the fixtures have been tested and validated against the specification.

The SFF-8431 SFP+ specification was written with the perspective that most design and test engineers use equivalent-time oscilloscopes. In reality, most designers prefer to use real-time oscilloscopes because it helps them to get into debug mode more easily. Also with oscilloscopes supporting bandwidths of more than 30 GHz with fast sampling rates, rise time and bandwidth is much less of a constraint than it was just a few years ago. However, the challenge is to interpret the specification in the context of a real-time oscilloscope compared to an equivalent-time model.

Another challenge to prepare for is that the SFP+ specification calls out some measurements to be performed using a PRBS31 signal. Some measurements (total jitter and eye-mask hit ratio) have PRBS31 as a recommended pattern. The maximum record length possible for acquisition with popular high-performance real-time oscilloscopes is 200 million samples. At a sampling rate of 50 Gsamples/s, the designer can acquire around 40 million unit intervals (UIs). At a sampling rate of 100 Gsamples/s, the instrument can acquire 20 million UIs. However, a PRBS31 pattern has more than 2 billion UIs. Hence, acquiring an entire pattern presents a challenge.

Additionally, acquiring a record length of 200 million data points demands huge processing power and time. One solution is to treat the PRBS31 waveform as an arbitrary waveform and acquire a modest record length of 2 million to 10 million UIs to recover the clock and compute the results. This provides a good tradeoff between processing power and test-result accuracy.

Because it provides a great amount of detail about the health of an SFP+ design, test engineers must master the TWDPc measurement. TWDPC requires a special algorithm, which the SFP+ specification defines.

This test is defined as a measure of the deterministic dispersion penalty due to a particular transmitter with reference to the emulated multi-mode fibers and a well-characterized receiver. The fiber-optics concept has been extended to quantify the channel performance of high-speed copper links, also known as "10GSFP+Cu." Do you want to know more information about SFP+ transceivers or want to buy some fiber optic products.I think Fiberstore can help you.