# Jitter Analysis Record Length Requirements

The Jitter analysis software always requires the source waveform record to contain at least two complete data patterns in order to calculate jitter results that are correlated to the data pattern (DCD, ISI, DDJ). Sometimes it may require more, depending on the clock recovery method being used.

Jitter analysis requires that the minimum number of UIs captured in a single acquisition is approximately 30,800. If this requirement is not met then the results field will display "too few points".

In periodic data mode, the Jitter analysis software requires the source waveform record to contain at least 2048 logic transitions in order to calculate jitter results that contain components that are uncorrelated to the data pattern (RJ, PJ, DJ, TJ). Sometimes it may require more, depending on the clock recovery method being used. The message "acquisition skipped" is displayed in place of the measurement results when the source waveform record length is insufficient to calculate that particular result.

The number of complete data patterns in the source data waveform can be increased by increasing the oscilloscope's acquisition memory from within the Acquisition setup dialog box.

In some cases, the acquisition memory depth is sufficient to calculate a particular result, but is insufficient to calculate it on a single acquisition. In those cases, "incomplete" will be displayed until a sufficient amount of data is collected to calculate the result.

Also, a minimum number of accumulated transitions (approximately 154,000) from all acquisitions must occur before the first RJ, PJ, DJ, and TJ results are displayed.

Note that some software clock recovery settings reduce the amount of the source waveform on which jitter can be measured. Software phase-locked loop (PLL) clock recovery with a low-frequency loop bandwidth, for example, will take many bit periods to settle, and the clock reference must settle before jitter measurements can begin.