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DS64BR111: Interface between CML and LVPECL

Mikael Carlsen
Intellectual 270 points
Part Number: DS64BR111

Hi,

We will use the DS64BR111 in an fibre channel application.

Question 1:

Some of the received channels will have LVPECL. Do I need external termination for adapting to the CML input?

Question 2:

Also, on the output with CML, there will be inputs with LVPECL on the other end. Shall I terminate external for driving this input?

Question 3:

The application will be in a harsh environment, do you recommend putting common mode chockes on the input and outputs?

Question 3:

Do I need to put series resistors on the output for impedance matching?

Br Mikael

  • 0
    TI__Mastermind 43795 points

    Hi Mikael,

    Q1:  The inputs of the DS64BR111 do require AC coupling to isolate the LVPECL signal common mode voltage from the DS64BR111 common mode input bias.  Other than the AC coupling, no additional termination should be needed.

    Q2: The outputs of the DS64BR111 will not require external termination to drive this load.  They will require AC coupling because the DS64BR111 output common mode voltage is not compatible with the LVPECL input voltage requirement.

    Q3:  I have seen the use of common mode chokes in extreme automotive environments.  Using chokes in enterprise computing applications is not typical.  I would recommend using a very high bandwidth choke since the DS64BR111 outputs do have relatively fast transition times.

    Q3: I would not expect to see series resistors for impedance matching.  The internal terminations on the DS64BR111 are designed to work with 100 Ohm differential signals.

    Fiber Channel up to 8G is 8b10b encoded, so I do not see any issues with AC coupling on our side of the interface.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Intellectual 270 points

    Hi Lee,

    Thanks a lot for the answers. They solved my concerns.

    Br Mikael