Other ways to think about jitter
There are other ways of visualising jitter, and applying several of them to a signal can help identify the sources of jitter.
A histogram plots the range of values exhibited by a parameter along the x-axis versus the frequency of its occurrence on the y-axis. In jitter analysis, histograms can plot waveform parameters such as rise time, fall time, period, or duty cycle, to reveal conditions that can be correlated with circuit conditions.
The histogram in Figure 3 shows period jitter in a clock signal. The double peak at right suggests that the signal includes second and fourth harmonics.
The bathtub plot
The bathtub plot in Figure 4 graphs the bit error rate (BER) of a signal versus its sampling point. The horizontal scale represents the time it takes for one symbol to be transmitted. BER is represented on a vertical log scale.
When the sampling point is at or near the transition points (0 and TB), the BER is 0.5 meaning it is equally likely that a bit will or will not be transmitted successfully. The curve is fairly flat in these regions, dominated by deterministic jitter. As the sampling point shifts away from the transition point, the BER drops off rapidly as the jitter becomes dominated by random processes. The bathtub plot shows that, as in Figure 1, the best time to sample the signal is halfway between its symbol’s transitions.