How to calculate clock jitter from phase noise

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

Application

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).

  

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

  

• 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

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