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total jitter equation clarification

J P
Intellectual 370 points

In this document  https://training.ti.com/sites/default/files/docs/tipl-4703-understanding-signal-to-noise-ratio-and-noise-spectral-density-in-high-speed-data-converters.pdf   on page 12:


1) in the total jitter equation is the "2" in the square_root in the equation to take into account the phase noise on both sides of the carrier? Due to symmetry, the jitter can be multiplied by 2 instead of having to measure the phase noise power on each side of the carrier out the +offset and -offset.


2) Note that this document has an error on page 12 in the equation for tau_j. In this equation the value for noise should be Phase Noise Power dB (NOT noise spectral density (dBc/Hz))

  • +1
    TI__Mastermind 24550 points

    Hi JP,

    You are correct, the '2' under the square root is included to represent the phase noise on both sides of the carrier.

    Jitter only reflects on the relative levels of the phase noise, meaning that the power level of the carrier is not important. This means that dBc is the preferred unit for this calculation as opposed to dB.

    The upper equation on page 12 is correct, but the bottom equation does incorrectly show the unit for phase noise power as (dBc/Hz) instead of (dBc).

    Regards