3 Cycle-to-Cycle Jitter

Measuring cycle-to-cycle jitter is very similar to measuring period jitter, but with one additional step. The standard procedure for measuring cycle-to-cycle jitter involves randomly measuring the duration of two clock periods 10,000 times and taking the absolute difference between the two. The recorded data is used to calculate the mean and standard deviation values, and the peak value is simply the largest difference in periods observed. As with period jitter, the peak-to-peak values can vary greatly and, often times, cycle-to-cycle jitter needs to be re-calculated several times to come up with an average value. Some digital oscilloscopes have a histogram feature, which simplifies much of the math.

Below is an example of cycle-to-cycle jitter measured on a LeCroy Waverunner 610ZI Digital Oscilloscope for a 50MHz XO. In this case, a jitter measurement tool, assigned to P8 and labeled ‘dper’, is used to calculate the cycle-to-cycle jitter. This analyzer platform is setup to measure 30,000 samples at a time and is executed three times in order to obtain an average peak-to-peak value.