e measured and plotted in a graph, for jitter the resultant frequency (or rate) of the phase variations is higher than 10 Hz (ten variations per second). Figure 5-9 shows one such example of jitter, where the y-axis shows the phase variations (in ns), and the x-axis shows the time of variation (in seconds) itself. As depic- ted in Figure 5-9, the rate of phase variations recorded is much higher than 10 Hz, and such phase variations are classified as jitter. seconds Figure 5-9 Plot of Phase Deviations Showing Jitter in a Clock Signal For wander, in a similar approach, a graph plotting the phase variations will show the frequency (or rate) of less than 10 Hz. It is important to note that the rate of phase variations for wander could go down to mHz or uHz (rate down to once in several minutes or hours). For this reason, it is always recommended to run wander measurement tests for long periods of time (hours or days). As you read in Chapter 3, the jitter (and wander to some extent) can be filtered out, and to do that, filters are used. If one configures an LPF with 10 Hz as the cut-off frequency, it will eliminate phase variation with a rate of variation higher than 10 Hz. Because jitter is defined as phase variation above 10 Hz, any LPF configured this way filters out jitter. Similarly, an HPF configured with a 10-Hz cut-off will filter out wander, because the HPF will filter out variations with a rate of 10 Hz or lower. Phase variations from a real-life test are captured in Figure 5-10, Figure 5-11, and Figure 5-12, which show, respectively: 1) phase deviations of a clock signal with jitter and wander present with no filter; 2) with an HPF filter applied; and 3) with an LPF filter applied. In these figures, the y-axis shows phase variations (in ns), and the x-axis shows the time elapsed since the measurement was started (in minutes). The graph shown in Figure 5-10 captures all the phase variations of a clock signal (low and high rate phase variations plotted in a single graph), and SO it is not easy to visualize th