Rise-Time Degradation and ISI Jitter

Figure 1: Shown are the signals from two extreme bit patterns
overlaid on top of each other with no interconnect in the channel

In discussing inter-symbol interference (ISI), the phenomenon in which information "leaks" from one bit to subsequent bits, we've identified a couple of root causes of ISI jitter. The first is reflection losses caused by impedance discontinuities, while the second is group delay dispersion, a consequence of the differing propagation speeds of different frequencies through a given material. We looked at these forms of distortion in both the time and frequency domains.

The Components of Total Jitter

Figure 1: An overview of the jitter hierarchy,
or "jitter tree," showing the various elements
that make up total jitter

In an earlier post, we began looking at the topic of jitter, a topic of keen interest to anyone working with high-speed serial communications or the components of such a system, including transmitters, receivers, and data channels. To gain an understanding of jitter, an important first step is getting to know a little about the various categories that comprise total jitter.