Ethernet conductor in PCB

Discussion in 'General Electronics Chat' started by Danna, Jul 23, 2011.

  1. Danna

    Thread Starter New Member

    Jul 23, 2011
    3
    0
    Hi,

    I want to pass ethernet conductors through a PCB,the input is from RJ-45 and the output is to a circular connector.
    Do I need to match impedances on the board? do I need to add capacitors/resistors?

    *I don't use the the trasmitted data, meaning I don't use PHY component.

    Thank you,
    Danna
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, you might do that, but you don't say what else will be on the board.

    CAT-5 cable has 4 twisted pairs inside; 2 pairs for data and 2 pairs for voice. The twisting keeps the signals from coupling to other pairs.

    If you run the signals across a board without some kind of shielding, they may pick up ambient noise or noise from the board; they won't be twisted any more unless you make the traces "twist".

    [eta]
    Here's an application note from Micrel: http://www.micrel.com/_PDF/Ethernet/app-notes/an-111.pdf
    You should have a look.
     
    Last edited: Jul 23, 2011
  3. Danna

    Thread Starter New Member

    Jul 23, 2011
    3
    0
    I also have on the board a lot of components (FPGA,prom,trancievers, clocks,SRAM,flash and etc).
    how do I keep the twisting on the board? Do I use 100ohm controlled trace and Keep both traces of each differential pair as identical to each other as possible?

    Thank you,
    Danna
     
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