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Original question:

DS110DF410 1G Fiber channel support?

DS110DF410: DS110DF410 support for 150 Ohm Fibre Channel

Dallas Clow
Intellectual 340 points
Part Number: DS110DF410

The DS110DF410 datasheet references support for Fibre Channel in several places.  However, standard Fibre Channel cabling is 150 Ohms and the DS110DF410 uses 100 Ohm termination at both the input and output and doesn't appear to have any ability to disable or change this termination.  We would like to use the part in a Fibre Channel application with 150 Ohm cabling.  Is there a recommended way to do this?

Our application is operating at 1.0625 Gbps.  Using a 25 Ohm series resistor for the each of the two RX inputs would probably make a reasonable approach for a providing 150 RX termination.  Placing a 300 ohm resistor in parallel with the 150 ohm characteristic differential impedance output traces should present a 100 ohm impedance to the driver, but would have some impact due to differing from 150 receiver load.  Is there a recommended way to address Fibre Channel 150 cables using this part?

  • 0
    TI__Guru* 92180 points

    Hi Dallas,

    Typical impedance for DS110DF410 - as you noted - is expected to be around 100-ohm. Therefor device has not been characterized in 150-ohm environment you noted.  At 1.0625Gbps data rate, there is a wide eye opening and I am thinking you can use a PI or T attenuator 6dB attenuator to go from 150-ohm to 100-phm impedance. Please note link below. Here you can use a PI Tee 6-dB attenuator to do this transformation.

    http://www.rfcafe.com/references/calculators/attenuator-calculator.htm

    Also, it would be a good idea to get one of the DS110DF410 evaluation board and check this before doing your own board.

    Regards,,nasser 

  • 0 in reply to Nasser Mohammadi
    Intellectual 340 points

    Nasser,

    This sort of impedance matching approach is common in the RF community, but most RF signals have very different Fourier content from digital signals and are typically evaluated differently (VSWR vs. ISI, etc.).  My understanding is that for continuous RF signals, this sort of thing can be evaluated in terms of VSWR and power loss, but for digital signals this type of circuit would need to be evaluated in terms of reflection coefficient and intersymbol interference.  My previous experience with signal integrity simulations has been that this type a circuit is not feasible in the time domain for digital signals.  Do you have any references that support using a circuit like this?

  • 0 in reply to Dallas Clow
    TI__Guru* 92180 points
    Hi Dallas,

    There are 6dB min loss pads being used in digital video industry and bandwidth is good enough up to 3Gbps - based on what i have seen. I have used these with no problem. You can check these on Pasternack site. However, DS110DF410 has not been characterized in 150-ohm differential impedance environment.

    Regards,,nasser