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CDCE62005: LVPECL output level specifications

John Donohue
Prodigy 20 points

Part Number: CDCE62005

For the LVPECL output, VOH maximum is spec’d as Vcc-0.88, or 2.42V at Vcc=3.3V. VOL minimum is  given as VCC-2.02, or 1.28V at Vcc=3.3V. This gives up to 1.14 V swing on each LVPECL output, or up to 2.28 V differential swing. Even if we assume nominal levels for VOH and VOL as midway between the MIN and MAX specs, we get 1.66 V differential swing.

So, what is meant by the specification: |VOD| Differential output voltage? It is specified to be between 610 and 970 mV. Is this intended as the differential peak-peak output swing? If so, it seems at odds with the value that we would compute from the combined VOH and VOL values for the individual outputs.

  • 0
    TI__Genius 16845 points
    Yes, |VOD| is the differential output peak-peak swing. |VOD| = UxP - UxN; in other words, differential output voltage magnitude is the difference between the output high level and low level.

    When the UxP and UxN signals have the same common mode level and single ended swing, it indicates that the single-ended swing is equal to the differential swing.

    I hope this information helps.

    Kind regards,
    Lane
  • 0 in reply to Lane Boyd
    Prodigy 20 points
    So if I understand correctly, VOD(p-p) would then be equal to 2 X| VOD|? This seems an odd way to specify differential output swing, but if this is the case, I guess it makes sense.
  • 0 in reply to John Donohue
    TI__Genius 16845 points
    The differential output swing is |VOD|. VOD(p-p) is not a datasheet parameter. What are you looking for with VOD(p-p) exactly?

    To reiterate the above, the UxP and UxN signals have the same common mode level and single ended swing; UxP(hi) = UxN(hi) and UxP(lo)=UxN(lo)

    This means that the single-ended swing is equal to the differential swing; |VOD| = |UxP(hi) - UxN(lo)| = |UxP(lo) - UxN(hi)| = UxP(hi) - UxP(lo) = |VOse|

    Kind regards,
    Lane