The way of calculating jitter of a clock signal from the phase noise measured with the signal analyzer is mentioned.

Application

Connection block diagram

Connection block diagram

Solution

  • The clock jitter is computable from the phase noise level measured with the signal analyzer.
  • The instantaneous jitter can also measured by real time acquisition.
    Moreover, it is also possible to obtain the RMS jitter for a long period of time by averaging.

    The spectrum shown at left is obtained when a clock signal with PLL is measured by the signal analyzer. In this case, the noise component which causes a clock jitter can be approximated by the area of shaded region. The clock jitter Cj (Deg) is obtained from the following equation based on the phase noise Pn (dBc/Hz) and the bandwidth Bw (Hz).

    Figure:式

    When the clock frequency is Fc [Hz] , the jitter time Tj [s] is as follows.

    Figure:式

  • In case of Fc=1GHz, the values of Cj and Tj based on typical phase noise and bandwidth are shown in table below.
  • Cj[deg]
    Phase noise
    [dBc/Hz]
    10kHz
    BW
    100kHz
    BW
    1MHz
    BW
    1MHz
    BW
    -60 8.10 25.62 81.02 256.23
    -70 2.56 8.10 25.62 81.02
    -80 0.81 2.56 8.10 25.62
    -90 0.26 0.81 2.56 8.10
    -100 0.08 0.26 0.81 2.56
  • Tj[ps]@1GHz
    Phase noise
    [dBc/Hz]
    10kHz
    BW
    100kHz
    BW
    1MHz
    BW
    1MHz
    BW
    -60 22.51 71.18 225.06 711.75
    -70 7.12 22.51 71.18 225.06
    -80 2.25 7.12 22.51 71.18
    -90 0.71 2.25 7.12 22.51
    -100 0.23 0.71 2.25 7.12

System configuration

Signal analyzerMSA538 x 1
Lithium-ion battery [MB400] x 1
SMA-SMA cables1.5m [MC303] x 1
Adapter N(P)/SMA(J) [MA306] x 1

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