时钟的一些笔记

Jitter measurements

1）Output jitter

Output jitter is a measurement of the jitter present on an output from a system.

It is specified in unit intervals and the result expressed as a Root Mean Square (RMS), or peak-to-peak value. RMS values give information about the total amount of average jitter present, while peak-to-peak results tell more about the effect on performance, as it is the extremes that can cause errors. 

2）Jitter tolerance

Jitter tolerance is a measurement to check the resilience of equipment to input jitter. A signal is generated with added sinusoidal jitter and applied to the DUT (Device Under Test).  

3） Jitter transfer

Jitter transfer is a measure of how much jitter is transferred between input and output of network equipment. typically allowing a maximum of 0.1 dB jitter gain.

Wander measurements

The longer-term phase variations ranging from 10 Hz down to micro-Hertz and below. While jitter is normally measured with reference to a clock extracted from the data signal, wander is measured against an external reference clock .The fundamental measurement is of Time Interval Error (TIE).Several results requiring intensive computation can be calculated from TIE according to the ITU-T G-series recommendations:

1）MTIE (Maximum Time Interval Error): The peak-to-peak variation of TIE within a defined observation interval  T

2）TDEV (Time Deviation): A measure of the spectral content of wander and again is a function of the observation interval T

3）Frequency Offset: A measure of the degree to which the clock frequency deviates from its ideal value.

4）Frequency Drift Rate: A measure of how the frequency offset changes with time (i.e. frequency stability).

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