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In electronics and telecommunications, jitter is the deviation from true periodicity of a presumably periodic signal, often in relation to a reference clock signal. In clock recovery applications it is called timing jitter. [1] Jitter is a significant, and usually undesired, factor in the design of almost all communications links.
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]
The group delay and phase delay properties of a linear time-invariant (LTI) system are functions of frequency, giving the time from when a frequency component of a time varying physical quantity—for example a voltage signal—appears at the LTI system input, to the time when a copy of that same frequency component—perhaps of a different physical phenomenon—appears at the LTI system output.
Position vectors r and r′ used in the calculation. Retarded time t r or t′ is calculated with a "speed-distance-time" calculation for EM fields.. If the EM field is radiated at position vector r′ (within the source charge distribution), and an observer at position r measures the EM field at time t, the time delay for the field to travel from the charge distribution to the observer is |r ...
In physics and engineering, the time constant, usually denoted by the Greek letter τ (tau), is the parameter characterizing the response to a step input of a first-order, linear time-invariant (LTI) system. [1] [note 1] The time constant is the main characteristic unit of a first-order LTI system. It gives speed of the response.
During an interval of time τ, as measured by the reference clock, the clock under test advances by τy, where y is the average (relative) clock frequency over that interval. If we measure two consecutive intervals as shown, we can get a value of ( y − y ′ ) 2 —a smaller value indicates a more stable and precise clock.
The most straightforward scheme uses a digital counter and a free-running crystal oscillator to time intervals with 1-clock ambiguity, resulting in output edge jitter of one clock period peak-to-peak relative to an asynchronous trigger. This technique is used in the Quantum Composers and Berkeley Nucleonics instruments.
In optics, jitter is used to refer to motion that has high temporal frequency relative to the integration/exposure time. This may result from vibration in an assembly or the unstable hand of a photographer. Jitter is typically differentiated from smear, which has a lower frequency relative to the integration time. [1]