When jitter is measured and specified, it is typically in ps (pico seconds) from some reference edge and possibly over some number of specified cycles. However, other units of measure can be used and are common in some applications. One way is to express the jitter as a % of the reference period. In many applications the reference period is call a Unit Interval (UI) and the jitter is specified as a ratio or % of the UI. Other measurements used are degrees where: 1 UI = 360 degrees = 1 period = 2 pie radians. A good way to understand the conversions is to take an example. Consider the OC-3 clock frequency of 155.52 MHZ with ±50ps of jitter, or a total jitter of 100ps.
One Period = 1/155.52MHZ = 1 UI = 6.43ns = 6430ps = 360 degrees = 2*3.1418 radians
Jitter as: ps =100ps
Jitter as ratio of UI = 100ps/6430ps = 0.01555 UI
Jitter as % UI = 100ps/6430ps = 0.01555 UI = 0.01555 UI * 100 = 1.555 %UI
Jitter as Degrees = 100ps/6430ps * 360 Degrees = 5.598 Degrees of Jitter
Jitter as Radians = 100ps/6430ps * 2* 3.1418 radians = 0.0977 radians of jitter
Refer to application note AN-840 for more details. For other questions not addressed by the Knowedge Base, please submit a technical support request.


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Application Notes & White Papers
AN-840 Jitter Specifications for Timing Signals Application Note PDF 442 KB