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DP83640 100BASE-FX PMD Input Threshold

SH
Intellectual 260 points

Hi!

Does anyone know what is the thresholds for the 100BASE-FX PMD input pair? The datasheet indicated that it is PECL implementation but I am thinking it should be LVPECL to be exact. Either way, the thresholds for the data input pair are not listed. The PMD output pair is listed as 0.3V-0.93V. I am assuming there will be a minimum threshold for the PMD input pair.

Thanks,

SH

  • 0
    TI__Intellectual 1885 points

    Hello,

    The fiber transmit and receive pins are differential and are designed to be LVPECL compatible.  In the case of the fiber transmit specification, the minimum output levels from the device should be 0.3V single-ended, 0.6V differential.  This signaling should meet the requirements of the fiber transceiver inputs.  Typically, the transmit signaling will be closer to 0.5V single-ended, 1.0V differential. 

    Thanks,

    John

  • 0 in reply to John Hamilton1
    Intellectual 260 points

    John,

    Thank you for the reply. I am also trying to make sure that the tranceiver signaling will meet the Ethernet Phy as well. I took some measurement and the tranceiver is sending at around 1.3-1.4V pk-to-pk. What is the minimum threshold for the Eth Phy INPUT?

    Thanks,

    SH

  • 0 in reply to SH
    TI__Mastermind 31600 points

    In 100Base-FX mode, the RD+/- pins are designed to accept LVPECL voltage levels.  The signals would nominally be 800mV (single ended). 

    Based on the results of our device characterization, the RD+/- pins should be able to accommodate signaling of 1.3 - 1.4 Vpp (differential) with some margin.  These signal levels should not pose any problems.

    Patrick