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SFP+ and QSFP media converter/repeater

Petr Czepiec
Prodigy 10 points
Other Parts Discussed in Thread: DS125BR820, DS100DF410, DS100KR800, DS110DF410

Hi,

I design SFP+ host to QSFP host media converter/repeater. Simply, the board where is four SFP+ cages on one side and one QSFP cage on other side, each SFP+ host connected to one channel in QSFP host (crossover RX -> TX and vice versa). Hosts must meet the condition SFF-8431 (or SFF-8436) hi-speed interface specification.

Primary, in SFP+ cages will be various optical modules and in QSFP cage will be copper twinax cable (up to 5m), but solution must meet the requirements for combination of copper cable or optical modules in each host. I expetimentaly try only passive solution and it (experimentaly) works with DELL optical modules in SFP+ hosts and max 0,5m copper cable in QSFP host.

I am thinking about simply design for solution with active components, place between SFP+ hosts and one QSFP host channels some repeaters (4+4 channels together). So, my question is, what is better to use as these repeaters, redrivers or retimers? I understand the difference, how both of them theoretically works, but I need advice for application usage. I am looking for TI products, e.g. DS125BR820 from redrivers or DS100DF410 family from retimers.

Thanks!

  • 0
    TI__Mastermind 19135 points

    Hi,

    Both the DS125BR820 and DS100DF410 can be considered for QSFP+-to-SFP+ media conversion application, but the standard and link requirements for your application need to first be examined. Additionally, TI has the DS100KR800 repeater which is suitable for backplane applications such as 10G-KR, but can also be considered for SFP+/QSFP+ front port. A couple of factors to evaluate when determining whether to use a repeater like DS125BR820 vs a retimer like the DS100DF410 are the max insertion loss to be supported (e.g. adding loss from PCB traces, module connectors and copper cable) as well as the need for link training support.

    • For 40GE side, 40G-CR4 physical media requires support of Rx-Tx link training.  The DS125BR820 and DS100KR800 work to extend the reach possible by using active linear equalization to the channel, boosting attenuated signals so that they can be more easily recovered at the Rx. The repeater outputs are specially designed to be transparent to Tx FIR signaling in order to pass information critical for optimal link training to the Rx. The DS100DF410 retimer on the other hand does not have a fully linear data path option and thus link training information is not passed through. Thus the DS100DF410 may be used for SR4/LR4 applications but not CR4.
    • The DS125BR810 implements a continuous time linear equalizer (CTLE) that is programmable from 3dB  to 10 dB at 6 GHz. The DS100KR800 provides receive equalization up to 36 dB at 5 GHz.
    • The retimer provides more advance signal conditioning. Specifically, in addition to a very high performance Rx CTLE it also has decision feedback equalization (DFE) for compensation of effects from reflection and crosstalk. The retimer implements clock and data recovery, and thus allows for the lowest possible jitter

    To provide further guidance, I would suggest looking at the DS125BR820 datasheet, which can be downloaded from TI.com. This doc has very detailed design recommendations for front port applications. You can then also look at the DS100KR800 and DS110DF410 datasheets as well, also downloadable from TI.com.

    Cordially,

    Rodrigo Natal

    DPS Applications Engineer