2.1. I/O Signaling Basics and Components

The particular signaling method used in a digital system has the most direct impact on signal integrity. It fundamentally determines how fast, efficient, and robust the digital system will be. In the past, relatively little attention has been paid to an optimized signaling method for high-speed data transmission, because overall system performance was not severely limited by I/O performance. With system data rates approaching multi-gigahertz, one must carefully choose the signaling method to achieve the desired system performance and robustness. This section introduces the basics of signaling from the perspective of high-speed I/O design and explains how each aspect of a signaling method affects signal integrity.

Signaling is a method used to translate digital symbols (1s and 0s) into physical quantities (voltage or current). A signaling system can be characterized by six basic elements: topology, transmitter, receiver, interconnect, termination, and clock. Many different signaling methods are available, based on different combinations of these six basic elements.