Electrical-link design is challenging due to the frequency-dependent loss and reflections associated with electrical channels as well as cross-talk between nearby channels. The equations describing lossless and lossy transmission lines are introduced in this chapter, followed by a brief discussion of loss mechanisms. The characteristics of various channels are presented, along with the effect of wirebonds and packages. The goal of this chapter is to provide link designers with a methodology to estimate the overall pulse response of a channel consisting of a lossy transmission line and the relevant package and chip parasitic elements. Knowing the pulse response, a link designer can then contemplate and model the equalization (discussed in Chapter 4) needed to properly detect transmitted bits. This chapter is organized to discuss transmission-line fundamentals and then overall channels.

In the previous chapter we discussed freely propagating waves: waves that propagate through a medium without any guidance from supporting conducting or dielectric surfaces. We can, however, effectively guide waves from a source to a load using a pair of parallel, uniform conductors known as a transmission line. Transmission lines consist of two or more conductors extending a long distance along one axis, and maintaining a uniform cross-sectional geometry in the plane transverse to this axis. In this chapter we will consider several different types of transmission line systems. Common examples that each of you has probably encountered in everyday experience are co-axial conductors, often used for delivering a signal from the cable provider to your TV; microstrip, often seen in printed circuit board applications; and twin-lead transmission lines, often used with portable “rabbit-ears” antennas for TV receivers. In this chapter we will explore the properties of waves on transmission line systems, including such important aspects as traveling waves, standing waves, characteristic impedances, impedance matching, losses, and much more.