Chapter 8. Transmission Lines and Reflections

TIP

If a signal is traveling down an interconnect and the instantaneous impedance the signal encounters at each step ever changes, some of the signal will reflect and some of the signal will continue down the line distorted. This principle is the driving force that creates most signal-quality problems on a single net.

These reflections and distortions give rise to a degradation in signal quality. In some cases, this looks like ringing. The undershoot, when the signal level drops, can eat into the noise budget and contribute to false triggering. One example of the reflection noise generated from impedance discontinuities at the ends of a short-length transmission line is shown in Figure 8-1.

Figure 8-1. “Ringing” ...

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