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LMK01801: Proper DC-coupling of CLKin pins

Joerg Reins
Prodigy 90 points
Part Number: LMK01801

Hello,

We'd like to know if the LMK01801 clock input can be safely DC-coupled to a differential clock source? Nothing about CLKin input common-mode voltage can be found in the datasheet, and AC coupling seems to be the one and only recommended scheme.

Does anybody have details about CLKin equivalent circuit?

On evaluation board we measured around 1.8V at the CLKin pins. So it seems that for instance 3.3V LVPECL driver format (VCM usually VCC-1.4V) could fit well to roughly match CLKin common-mode voltage level. Is this assumption correct?

Best regards,
Joerg

  • 0
    TI__Mastermind 28550 points
    Hello Joerg,

    I don't have data for phase noise floor impact with input common mode shift on LMK01801. However in general if you stick with a common mode voltage ~self bias voltage you would be fine. This bias does shift over temperature. My experience suggests, in general if you are above ~1.3 V Vcm, performance should be ok. However I cannot provide any guarantee for this type of operation without it being fully characterized and in datasheet.

    73,
    Timothy