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DS90LV804: GND level is different when connecting PCBs by using LVDS. Does this matter?

Hisao Uchikoshi
Genius 14960 points
Part Number: DS90LV804


Hi Experts,

We will connect several PCBs by LVDS on back-plane.  GND level of each PCBs are not same, meaning that LVDS driver IC GND is different.

Does this matter or not?

Regards,

Uchikoshi

  • 0
    TI__Mastermind 43795 points

    Hi Uchikoshi-san,

    The LVDS signals are GND referenced.  The LVDS output has a common mode of ~ +1.2V with respect to GND.  The input is designed to signals with a range of input common mode, usually from +0.05V to +2.4V above GND.  This allows for good noise rejection when using LVDS interfaces.

    How much GND difference do you see? 

    Large ground differences can be overcome with various forms of isolation (AC coupling or transformer coupling are two examples).

    Regards,

    Lee 

  • 0 in reply to Lee Sledjeski
    TI__Genius 10250 points

    Hi Uchikoshi-san,

    As Lee mentioned when using AC coupling (which is the case from the the circuit you shared with me off-line), then ground potential difference should not be an issue. However, please notice that to be able to use AC-coupling, the data needs to be DC-balanced (for example, using 8b/10b encoding, to make sure there are no long strings of 0 or 1).

    Regards,

    Yaser