I am designing a 4- layer PCB with Ethernet (RMI) and integrated magnetics, which I want to make as good as possible with respect to signal integrity and EMC.
RMI, so the frequency is 50 mHz.
Because of practical reasons I have a length mismatch between the Tx+- and Rx+- diff pairs of about 4 inch. (Note : only a mismatch between the pairs but not within one pair)

I found a lot of information online and on this website about length matching between Tx + and Tx - or Rx+ and Rx-, but not about the length mismatch between the two pairs (intra pair if I am correct).

Question : What effects does this mismatch have? Do I need to care about it with only 4 inches ?
If not, in which situation would I need to take into account ? and how?

  • \$\begingroup\$ 10baseT? 100baseT? \$\endgroup\$
    – vicatcu
    Commented Jan 5, 2020 at 3:27

1 Answer 1


Ethernet RX and TX pairs have literally nothing to do with one another. It's a full duplex channel. You would never need to concern yourself with this, because they are independent.

  • 1
    \$\begingroup\$ So because it is a duplex channel it does not matter if lengths are completely mismatched? \$\endgroup\$
    – Navaro
    Commented Jan 5, 2020 at 10:23
  • \$\begingroup\$ yea, they are separate, asynchronous, channels for sending and receiving data. The senders and receivers of data don't know anything about each other, or the routing topology a particular packet will follow between them, so how could the phase of information passing between them matter? \$\endgroup\$
    – vicatcu
    Commented Jan 5, 2020 at 16:44

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