A phase fluctuation of a signal is an oscillating movement with an amplitude and a frequency. Wander is defined as the phase error comprised in the frequency band between 0 and 10 Hz of the spectrum of the phase variation. If this frequency is higher than 10 Hz, it is known as Jitter. Jitter is the time variation characteristic of a periodic signal in electronics and telecommunications, often in relation to a reference clock source. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of periodic signals. Jitter is a significant and undesired factor in the design of typically all communications links. Jitter can be quantified in the same terms as all time-varying signals (RMS, Peak-to-Peak Displacement), also like other time-varying signals, Jitter can be expressed in terms of spectral density. Jitter period is the interval between two times of maximum or minimum effect of a signal characteristic that varies regularly with time. Jitter frequency, the most common figure, is its inverse. Very low Jitter frequency is not a standard interest in designing systems, and the low-frequency cutoff for Jitter is typically specified at 1 Hz.
Types of Jitter
- Random Jitter or Gaussian Jitter, is an unpredictable electronic timing noise.
- Deterministic Jitter is a type of clock timing Jitter or data signal Jitter that is predictable and reproducible. (AKA Periodic Jitter, Data-Dependent Jitter or Duty-Cycle Dependent Jitter)
Testing for Jitter and its measurement is of great importance to electronics engineers because of the ever increasing clock frequencies in digital electronic circuits aimed at achieving higher device performance. Testing of device performance for Jitter tolerance often involves the injection of Jitter into electronic components with specialized test equipment. Jitter is measured and evaluated in various ways depending on the type of circuitry under test and the goal of Jitter measurement is to verify that the Jitter will not disrupt normal operation of the circuitry.
Some popular T&M equipment used for Jitter testing:
Lecroy WavePro 715Zi Digital Oscilloscope with the Jitter and Timing Analysis Package (WPZi-JTA2) WPZi-JTA2 adds Specialized timing parameters measure period, cycle-cycle, half period, width, etc. Jitter on a variety of signals. Use the three views of Jitter (statistical, time, and frequency) to understand root cause and to debug problems. Histograms provide understanding of statistical distributions. Tracks provide a means to show time-correlated peaks of Jitter, and compare to other signals. FFTs provide the ability to debug root causes of high in-circuit Jitter.
Agilent 37717C Communications Performance Analyzer can be configured as a dual standard SONET/SDH analyzer for BER and Jitter tests which makes it the ideal tool for testing network equipment in a manufacturing environment.
Rohde & Schwarz UPV Audio Analyser includes Jitter analysis and interface testing.
Tektronix CSA7154 Communication Analyzer offers complete Eye Pattern Measurements Suite Including Extinction Ratio, Q-factor, Eye Height/width, Jitter and Noise
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