Introduction to Debugging High-Speed Serial Links

Figure 1: These images depict the degradation of serial data
traffic as it makes its way from transmitter to receiver

In recent years, the data rates in serial links have increased exponentially across any number of standard protocols, including PCI Express, USB, and even SATA and SAS. With higher data rates comes more challenges for system designers, validation engineers, and test engineers with respect to signal integrity (SI). Some SI effects are much more prominent at higher data rates than they were for lower-speed versions of the same protocols. In this series of posts, we'll examine these SI effects, look at some methods of improving system performance, and discuss some SI analysis solutions as well as measurement considerations.

The History of Jitter (Part V)

Figure 1: Applying PLLs for clock-data recovery is not
unlike tapping your feet to the beat of music

A milestone in the history of jitter measurement came in the 1990s with receivers that could reveal the slowly varying component of jitter that became evident in time-interval error (TIE) tracks. That led to the advent of using phase-locked loops (PLLs) for clock-data recovery. In turn, PLLs opened new horizons in jitter analysis.

The History of Jitter (Part III)

Figure 1: Latching a signal at the outermost of the blue

hash marks results in a BER of 10^-3, while latching it

at the innermost hash marks yields a BER of 10^-12

If you've been keeping track of our history of jitter, we left off in Part II in the late 1990s, by which time bit-error rates (BER) had become a predominant statistic for quantifying jitter. That was subsequently refined into thinking in terms of BER as a function of jitter.

The History of Jitter (Part II)

Figure 1: An example of using histograms to plot
the statistical distribution of edge arrival times

Resuming our review of the history of jitter and the evolving response to it, we'd arrived at the late 1990s, when more sophisticated analysis methods were necessary to get a good handle on jitter. In particular, statistical analysis came onto the scene. Statistics are a great tool for analyzing phenomena such as jitter that change more as you look at them harder.

Using Histograms (Part II)

Figure 1: A flip-flop's propagation delay is a typical spec

that can be derived using statistical analysis

In Part I of this series, we looked at some of the basics of histograms and how they can provide a statistical view into random variation of signal parameters. Next, let's look at how histograms can help us use statistical analysis to determine product specifications.

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.