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CDCM6208 LVDS output DC coupling

fdm
Expert 1070 points

Other Parts Discussed in Thread: CDCM6208

Hi,

Why there's the recommendation in the CDCM6208 DS p.67 (10.2.2.6 Device Output Signaling): "The LVDS-like outputs should be AC-coupled when interfacing to a LVDS receiver."?
May the LVDS type output of CDCM6208 (1.8V powered) be DC-coupled with LVDS input buffer (100 Ohm differential load)?

BR,
 Denis

  • 0
    TI__Mastermind 32575 points
    Denis,

    CDCM6208's LVDS-like (and LVPECL-like) differential output driver modes are actually implemented using VDD-referred CML output topology with programmable voltage swing. Because these outputs modes are CML-based, they have a output common mode voltage (Vocm) level that's near the VDD_Yx voltage. This Vocm may not be compatible with LVDS input buffer, so it's suggested to AC couple the outputs for DC blocking. This means the LVDS input will need to establish the input common mode voltage, either through internal or external biasing.

    Alan
  • 0 in reply to Alan O
    Expert 1070 points

    Alan,

    What is the VCM-AC parameter with value of (VDD_Yx_Yy - 0.76) for LVDS-like output that is 1.04V for VDD=1.8V?

    Denis