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DP83867CR: About pattern impedance

tatsuro tokugawa
Prodigy 130 points
Part Number: DP83867CR


Hi,

Could you tell me pattern impedance mentioned in attached file.

A single pattern impedance is 50ohm(to GND)?
A differential impedance is 100 ohm(between patterns), and it's necessary characteristic to be 50ohm(to GND)?

Thanks.

  • 0
    TI__Mastermind 26025 points

    Hi tatsuro,

    RGMII signals are single ended. PHY drive it through 50 ohms driver (output pin) but on the receiver side of the PHY (input pin) there is no termination. Hence the traces on the output pin of PHY are recommended to have 50 ohms single ended impedance. The differential impedance constraint is for differential signal.

    Regards,

    Hillman Lin

  • +1 in reply to Hillman Lin
    Prodigy 130 points

    Hillman-san

    Thank you for your reply.

    > PHY drive it through 50 ohms driver (output pin) but on the receiver side of the PHY (input pin) there is no termination.
    Is it necessary to mount a 50ohm resistance on the side of PHY to terminate?

    > The differential impedance constraint is for differential signal.
    I think in case of a differential signal, the impedance between the pattern should be 100ohms. Is it necessary to make each of them single 50ohm at the same time?

    Best regards.

  • 0 in reply to tatsuro tokugawa
    TI__Mastermind 26025 points

    Hi tatsuro,

    • No, you should not mount the 50 ohms resistor. RGMII load can only be capacitive.
    • No, only the 100 ohms impedance are sufficient

    Regards,

    Hillman Lin