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CDCLVD1204: Functionality of VAC_REF pin

Ella KIM
Expert 3862 points
Part Number: CDCLVD1204
Other Parts Discussed in Thread: LMK01000

Hi team,

I have a question on VAC_REF pin of CDCLVD1204. I believe it provides reference voltage for AC-coupled differential input as CDCLVD1204 receiver is not internally biased. Is my understanding correct?

I also found several clock buffer devices that don't have this VREF pin. If I choose those parts, do I need additional power supply rail on the board for VCC/2 biasing? Can I say that CDCLVD1204 is competitive than the competitor's part that doesn't support VREF pin functionality?

Thanks!

  • +1
    TI__Mastermind 28530 points

    Hello Ella,

    Ella KIM said:
    VAC_REF pin of CDCLVD1204. I believe it provides reference voltage for AC-coupled differential input as CDCLVD1204 receiver is not internally biased. Is my understanding correct?

    You are correct.

    Ella KIM said:
    I also found several clock buffer devices that don't have this VREF pin. If I choose those parts, do I need additional power supply rail on the board for VCC/2 biasing?

    Probably not.  (1) if DC coupling, then the driver sets the common mode.  if (2) AC coupling, then the datasheet should describe (or prescribe AC coupling of inputs as in case of LMK01000 for example) so that the internal biasing can work.

    When LVDS is driven DC coupled, then there is not need for any reference as the driver sets the common mode voltage. 

    Ella KIM said:
    Can I say that CDCLVD1204 is competitive than the competitor's part that doesn't support VREF pin functionality?

    I don't think you can say that.  Now for LVPECL receiver which provides a VREF, that could be considered an advantage.  But I don't think for LVDS... unless the other device does not have proper internal biasing when AC coupled and no VREF.  Then it could be used in DC coupled applications only.

    73,
    Timothy