# Signal Jitter

Pulse Rise Time Jitter

Jitter is the difference [deviation] between the expected occurrence of a signal edge and the time the edge actually occurs [phase variation].
Jitter may also be expressed as the movement of a signal edge from its ideal position in time [the expected position].
The jitter edge may lead or lag the expected position. Information signal variations relative to a reference time position.
Jitter appears as two distinct types; Deterministic Jitter, and Random Jitter.
Deterministic jitter can be caused by power supply fluctuations, power line noise, cross-talk, and duty cycle distortion (asymmetric rising and falling edges).
Random jitter is caused primarily by device thermal noise. If the Jitter frequency is below 10Hz then it's called wander, but it's still jitter.
Many types of jitter definitions use the term UI [Unit Interval], which translates into the [smallest] bit interval.
Jitter is not the same as Timing Skew. Signal variations can be in time, frequency or phase.
Time jitter is measured at the 50 percent voltage point.

Average Jitter = root-mean-square [rms] Jitter.

Cycle-to-Cycle Jitter: Relates the jitter-ed edge of the current cycle to the transition of the previous cycle.
The difference in length from one clock cycle to the next cycle.

Deterministic Jitter [DJ]: Jitter with a non-Gaussian probability density function. Always bounded in amplitude and with specific causes.
DJ is characterized by its bounded, peak-to-peak [p-p], value.
Deterministic Jitter, is repeatable [so deterministic] being caused by a fixed or specific events.

Jitter amplitude: Fluctuations in the amplitude of the signal, and not normally a concern in digital logic.

Jitter frequency: is the inverse of jitter period, which would than be the time to compete a cycle.
Which could either be the max to max deviation or min to min deviation.

JitterPeak-to-Peak[p-p] = Jittermax[ps] - Jittermin[ps]

Jitter[UI] = Jitter [ps] / 1UI [ps]

Maximum Tolerable Jitter [MTJ]

Peak-to-Peak Jitter [p-p] = Jittermax[ps] - Jittermin[ps]

Period Jitter: The maximum change of the signal edge from the expected of ideal position in time.
The change in the transition point from its ideal position over consecutive clock cycles.

Phase Jitter [Long Term Jitter]: The maximum change of the signal edge from the expected of ideal position over many cycles.

Random Jitter [RJ]: Jitter that is described by a Gaussian probability distribution, characterized by its standard deviation value (rms).
Random jitter [being random] is not predictable and the opposite of deterministic jitter.

Total Jitter [TJ]: = DJ + RJ

UI: Unit Interval is equal to one bit time. UI is the reciprocal of baud rate.

Period Jitter

Short term jitter is the deviation of the clock edge from its ideal position over a few consecutive clock edges.
Long term jitter is the deviation of the clock edge from its ideal position over a number of clock edges.

Specifications that deal with Jitter
ANSI T1.105.03 Telecommunications - Synchronous Optical Network (SONET) - Jitter at Network Interfaces
ITU G.825 The control of jitter and wander within digital networks which are based on the synchronous digital hierarchy (SDH)
ITU G.823 The control of jitter and wander within digital networks which are based on the 2048 kbit/s hierarchy
ITU G.824 The control of jitter and wander within digital networks which are based on the 1544 kbit/s hierarchy
ITU G.825 The control of jitter and wander within digital networks which are based on the synchronous digital hierarchy (SDH)

BIT Error Rate definition.
PRBS definition.
Are a few of the terms defined in the engineering dictionary.

Modified: 12/25/11