Articles

Jitter – Signal timing displacement from its ideal location

Jitter, Accumulated – Also known as Accumulated Phase Displacement, this measurement requires a series of hundreds to thousands of fully adjacent cycles. The accumulated jitter at any cycle is the difference between the actual arrival time of that cycle and the ideal arrival time of that cycle.

Jitter, Peak (or Peak-to-Peak) – The absolute difference in length between the longest cycle ever seen and the shortest cycle ever seen. This has been a traditional metric of system or device performance because it can be measured with less sophisticated equipment. Note that there is no pathological failure mechanism associated with peak jitter.

Jitter Tolerance – The amount of jitter a component, device or system may tolerate without experiencing a failure.

Jitter Transfer – The ratio of amplitude of a component, device or system's output jitter to the applied input jitter amplitude.

Repeatability – The total error that the measurement system will possibly add to the measurement. Components of repeatability include, but are not limited to, (depending on the system) resolution, timebase accuracy, trigger jitter, quantization noise, aliasing, interpolation and operator/environmental effects. Any result presented by a measurement system can be thought of as the sum of the actual jitter of the device "+" the repeatability of the measurement system.

Resolution – The level to which a value can be measured. Note that this is very different from repeatability. For example, a measurement system may have a resolution of 1 femtosecond, but a repeatability of 25 picoseconds. So a complete jitter result from this system might be written as 51.342±25 picoseconds. Obviously, resolution only needs to be good as repeatability - anything more is wasted.

Sampling, Equivalent Time – Also known as Repetitive Sequential Sampling. A sampling methodology in which the scope constantly arms, triggers, waits a specific time, acquires a single data point, then repeats the process. by constantly varying the wait time, an image of the waveform can be built up on the screen point by point. The disadvantage of this method is that it is not capturing cycles, and is therefore incapable of doing cycle-cycle measurements.

Sampling, Real Time – A sampling methodology in which the scope is armed and triggered once. This triggering causes the acquisition of a large number of sample points at preset intervals for the 54720 scope with 54721 plug-ins at max sample rate, 128K points at 250 psec intervals). This waveform record contains hundreds to thousands of adjacent cycles, which can be processed by M1™ to find cycle-cycle and accumulated jitter.