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DP83869HM: Rx / Tx diff impedance - 100Base-X / 1000Base-X / SGMII

viktor zalud
Prodigy 140 points
Part Number: DP83869HM
Other Parts Discussed in Thread: DP83869

Tool/software:

Hello,

I would have question to the Rx input and Tx output impedance for modes 100Base - X / 1000Base-X / SGMII. In the datasheet is define only Rx input impedance as 80 / 100 / 120R. My question is why this impedance has such with range and if this is really realistic. What are real the worst case measured values? My expectation is when the driver in design at 100R characterized impedance, the all samples shall not be far away from 100R. The second question is what it Tx output impedance, this is not in datasheet at all. Or at least I did not found it. I am asking because we must user two PCB for such high speed signal as this wide range shows that make us problem during simulation. 

  • 0
    TI__Mastermind 25955 points

    Hi,

    Thank you for reaching out. Let me confirm with the team on the data. We will get back to you sometime next week.

    We have work on 100Base-X/ 1000Base-X/SGMII with DP83869 with alot customer and we did no see any issue with the signal quality of on the Rx lines. 

    --

    Regards,

    Hillman Lin

  • 0 in reply to Hillman Lin
    Prodigy 140 points

    ok, thank you.....we have complicated case where we have several PCB and any big variation of Rx / Tx termination make the simulation resul not good. So I would like to know what is really possible range of Rx / Tx termination

  • 0 in reply to viktor zalud
    TI__Mastermind 25955 points

    Hi Victor,

    I check it with the team internally. IEEE specification define this input impedance form 80ohms to 120ohms fall within the specification.

    The IC impedance normally have higher tolerance.

    --

    Regards,

    Hillman Lin

  • 0 in reply to Hillman Lin
    Prodigy 140 points

    Ho Lin,

    thank you for reply. So this PHY really has this 80 / 100 / 120 impedances. Why I am asking, it is very common that vendor of IC give to datasheet some margin for safety reason. But for our simulation really would help us what it real case. it the Ic was design to the 100R as characterize impedance, form technical point of view, the 20% tolerance seem to be kind of much

  • 0 in reply to viktor zalud
    TI__Mastermind 25955 points

    Hi victor,

    It is really hard to control the impedance within ICs. In normal IC development, impedance tolerance should be around 20%.

    --

    Regards,

    Hillman Lin