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CDCI6214: LVDS output

Yusuke Mukuno
Expert 7395 points
Part Number: CDCI6214

Hi Expert,

The customer set Y4 to LVDS100MHz and checked the waveform on the customer's board.
The amplitude is about 0.7V as shown below.

Customers use 0.1μF ceramic capacitor on Y4P and Y4N lines for AC coupled.

The datasheet is descripted about maximum amplitude(DC coupled)  0.45V. Could you tell us why this value is exceeded?

(differential probe)

Thanks

Muk

  • 0
    TI__Mastermind 18070 points

    Hi Muk,

    First please make sure that there's 100Ohm across P and N channel or 50Ohm to ground on both. If the amplitude is still too high, then please reduce chx_lvds_cmtrim_inc (R59[12:11]) and/or increase chx_lvds_cmtrim_dec (R59[10:9]). The former register increments LVDS amplitude and the latter decrements it.

    Regards,
    Hao

  • 0 in reply to Hao Z
    TI__Expert 7395 points

    Hao-san

    Thank you for your comment.

    Customer use 100ohm resister between P and N channel.

    Also, customer is using AC coupling with 0.1uF. Is it no problem?  

    Now, chx_lvds_cmtrim_inc (R59[12:11]) is set 00.

    Customer will try to  increase chx_lvds_cmtrim_dec (R59[10:9]).

    Thanks

    Muk

  • 0 in reply to Yusuke Mukuno
    TI__Expert 7395 points

    Hao-san,

    Do you have any comment for below?

    >customer is using AC coupling with 0.1uF. Is it no problem?  

    Thanks

    Muk

  • 0 in reply to Yusuke Mukuno
    TI__Expert 7395 points

    Hao-san,

    Also, customer tried to  increase chx_lvds_cmtrim_dec (R59[10:9]).

    However, LVDS output amplitude is not improved.

    Could you please give your advice?

    Also, could you please give me your comment for below?

    >>Customer is using AC coupling with 0.1uF. Is it no problem?  

    Thanks

    Muk

  • 0 in reply to Yusuke Mukuno
    TI__Mastermind 18070 points

    Hi Muk-san,

    Yes AC coupled LVDS is fine. This is likely to be a measurement issue. Please check that the customer is using a passive probe that doesn't have internal amplification. Besides, please make sure that the 100Ohm internal resistor is enabled.

    Regards,
    Hao