Glossary term
Jitter
Short-term timing variation of signal edges, samples, packets, or clock events from their ideal positions.
Definition
metricJitter is short-term deviation in the timing of signal transitions, samples, packets, or clock events from their ideal time positions.
Jitter appears in digital communications, clock distribution, data converters, radar, networking, audio, high-speed serial links, and sampled measurement systems. It can be random, deterministic, periodic, data-dependent, bounded, or unbounded depending on source. Excessive jitter reduces timing margin, increases bit-error rate, degrades sampling accuracy, broadens spectra, and can turn amplitude noise into timing uncertainty.
Jitter is variation in event timing. In a digital link, it is the difference between when a signal edge actually occurs and when it should occur. In a clock, it is timing uncertainty from cycle to cycle or relative to an ideal reference. In packet networks, the term can refer to variation in packet delay. The common idea is that timing is not perfectly regular.
Sources
Random jitter comes from noise processes such as thermal noise, flicker noise, and oscillator phase noise. Deterministic jitter comes from identifiable mechanisms such as duty-cycle distortion, power-supply noise, crosstalk, inter-symbol interference, electromagnetic interference, reflections, bandwidth limits, and data-dependent transitions. Periodic jitter is often linked to switching regulators, rotating machinery, spread-spectrum clocks, or interfering clocks.
In sampled systems, aperture jitter in the sampling clock creates amplitude error. The faster the input signal changes, the more timing uncertainty becomes voltage error. This is why clock jitter limits high-frequency analog-to-digital converter performance even when quantization resolution appears adequate.
System effects
In digital communications, jitter reduces eye-diagram opening and timing margin. If the receiver samples too close to a transition, bit errors increase. In clock distribution, jitter can accumulate through phase-locked loops, buffers, connectors, and traces. In radar and RF systems, timing jitter can broaden spectra, raise phase noise, and degrade range or Doppler precision. In real-time networks, packet-delay jitter affects control loops, audio/video streaming, and synchronization.
Measurement
Jitter can be reported as RMS jitter, peak-to-peak jitter, time interval error, phase noise integrated over a bandwidth, or unit interval fraction. These measures are not interchangeable. RMS jitter is useful for random Gaussian-like uncertainty. Peak-to-peak jitter depends strongly on observation time. Phase-noise integration depends on offset-frequency limits.
Common mistakes
A common mistake is quoting one jitter number without bandwidth, observation interval, reference clock, and measurement method. Another is confusing jitter with latency. Latency is delay; jitter is variation in delay or event timing. A system can have high latency but low jitter, or low average latency but unacceptable jitter.