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For example, UI is used to measure timing jitter in serial communications or in on-chip clock distributions. This measurement unit is extensively used in jitter literature. Examples can be found in various ITU-T Recommendations, [1] or in the tutorial from Ransom Stephens. [2]
Jitter period is the interval between two times of maximum effect (or minimum effect) of a signal characteristic that varies regularly with time. Jitter frequency, the more commonly quoted figure, is its inverse. ITU-T G.810 classifies deviation lower frequencies below 10 Hz as wander and higher frequencies at or above 10 Hz as jitter. [2]
It is used to specify clock stability requirements in telecommunications standards. [1] MTIE measurements can be used to detect clock instability that can cause data loss on a communications channel. [ 2 ]
In that approach, the measurement is an integer number of clock cycles, so the measurement is quantized to a clock period. To get finer resolution, a faster clock is needed. The accuracy of the measurement depends upon the stability of the clock frequency. Typically a TDC uses a crystal oscillator reference frequency for good long term stability.
Clock synchronization is a topic in computer science and engineering that aims to coordinate otherwise independent clocks. Even when initially set accurately, real clocks will differ after some amount of time due to clock drift , caused by clocks counting time at slightly different rates.
PPS signals are used for precise timekeeping and time measurement. One increasingly common use is in computer timekeeping, including NTP.Because GPS is considered a stratum-0 source, a common use for the PPS signal is to connect it to a PC using a low-latency, low-jitter wire connection and allow a program to synchronize to it.
This of course means that the clock skew between two points varies from cycle to cycle, which is a complexity that is rarely mentioned. Many other authors use the term clock skew only for the spatial variation of clock times, and use the term clock jitter to represent the rest of the total clock timing uncertainty. This of course means that the ...
The stored data are used to control phase and frequency variations, allowing the locked condition to be reproduced within specifications. Holdover begins when the clock output no longer reflects the influence of a connected external reference, or transition from it. Holdover terminates when the output of the clock reverts to locked mode condition.