1 Reply Latest reply on Jul 22, 2014 6:08 AM by strangd

    Regarding Driver Impedance


      Hi Everybody,


      Is the driver impedance of the IC  and the Characteristic impedance of board trace is having relation between them?

      Suppose we have IMX6 IC which is having 34 ohm,40 ohm & 60 ohm driver impedance option and for our board we have

      to maintain 50 ohn characteristic impedance for single ended lines ? which one of the Driver impedance of IC will be more

      suitable for simulation.


      Does these Driver impedance of IC and trace characteristic impedance holds any relation?

      do we have to do like that Driver impedance of IC + Series Resistor = Trace characteristic impedance?


      Kindly guide me.


      Thanks & regards

        • 1. Re: Regarding Driver Impedance

          For the best transmission line signal integrity, the IC + the series resistor should equal the trace impedance.


          As for the design of transmission lines for any board layer that is another question. Unless there is a specification for a type of signal like 60ohm memory, 90ohm USB, 109-118ohm SATA, etc., then there is no “must have” trace impedance number like 50ohm that you need to design into the board.  What does matter to the transmission line is that the impedance does not vary from end to end.  So if you are setting up a lot of 60ohm memory routes in your board.  Set all to the traces to be 60ohm and adjust the value of the series resistors up so that drive impedance +series resistor equals 60ohm.  And if the driver is 60 ohm, then you can save parts.


          Have fun