How is "UI" defined and what is its significance in reference to jitter?

Description

The acronym UI stands for Unit Interval and it is a specification unit for jitter used to determine the maximum delta time of an arriving clock.

Clock signals have an average period, but any given transition can arrive slightly before or after an expected transition due to jitter. This delta time before or after an expected transition is calculated by multiplying the UI value by the average period.

For example, a 100 MHz clock has an average period of 10ns. If the maximum UI jitter = 0.025 UI, the maximum delta time will be:

10 ns x 0.025 UI = 250 ps (maximum delta time)

In equation form:

maximum delta time = average period x jitter (specified in UI)