In the frequency domain
Looking at the frequency distribution of jitter spectra can reveal deterministic jitter sources, which appear as line spectra. This approach can also reveal phase noise or jitter-versus-frequency offsets from a carrier or clock.
Phase-noise measurements provide insights into phase-locked-loop or crystal-oscillator designs, and can help identify deterministic jitter due to spurious signals. Such measurements can help optimise clock-recovery circuits and reveal internal noise sources.
Figure 5 shows the intrinsic jitter spectrum of a phase-locked loop. The noise peaks at a 2 kHz offset. There are also lines that identify deterministic jitter sources from 60 Hz to approximately 800 Hz, probably generated by the power lines. Frequency lines are also evident from 2 to 7 MHz, probably derived from the reference clock. Another way to obtain a frequency-domain view of jitter is to take a fast Fourier transform (FFT) of the time interval error data (the phase difference between the signal being measured and the reference clock), an approach that can reveal high-level phenomena quickly.