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Measuring non-terminated LVDS outputs.

Peter Perez
Prodigy 30 points
Other Parts Discussed in Thread: SN65LVDS100

If I do not terminate the LVDS outputs with a 100 ohm resistor, can I still measure one of the outputs by using a single-end measurement with the O-scopes 50 or 1 M ohm impedance setting. See attached file. If so, what is the voltage swing?

 If not, can I still make the same measurement if I add the 100 ohm termination? What is the voltage swing? Thanks.

 

 

  • 0
    TI__Mastermind 20820 points

    Hi Peter,

    Yes, you can still measure a single ended LVDS signal on a scope using the 50ohm termination setting. What I had to do to measure this properly was use an offset voltage equal to the common mode voltage that I was interested in. For instance, I drove 1.2V into my devices ground which shifted my down by VOD down by1.2V allowing the output of my device to drive a 50ohms to ground load. My output swing for this was ~350mV.

    This techniques worked well for me using TIs SN65LVDS100 EVM but it is not recommended for all parts.  

    Regards,

    Mike

  • 0 in reply to Michael Peffers
    Prodigy 30 points

    Thanks Mike,

    You mentioned the voltage swing would be ~175mV for the 50 ohm termination. Will the voltage range swing from 0 to 175mV or 1.2V to 1.375V or some other range when measuring one of the LVDS outputs single-endedly?

    Thanks again, Peter 

  • 0 in reply to Peter Perez
    TI__Mastermind 20820 points

    Peter,

    I did some lab testing this morning and adjusted my original response to you. Please let me know if you have anymore questions.

    Regards,

    Mike