10
TOPICS IN HIGH-SPEED CHANNEL MODELING
10.1 Creating a Physical Transmission-Line Model
10.1.1 Tabular Approach
10.1.2 Generating a Tabular Dielectric Model
10.1.3 Generating a Tabular Conductor Model
10.2 NonIdeal Return Paths
10.2.1 Path of Least Impedance
10.2.2 Transmission Line Routed over a Gap in the Reference Plane
10.2.3 Summary
10.3 Vias
10.3.1 Via Resonance
10.3.2 Plane Radiation Losses
10.3.3 Parallel-Plate Waveguide
References
Problems
So far, we have covered numerous topics that are required for the design of modern high–speed digital systems. There are a few important topics, however, that do not fit nicely into the flow of the other chapters. This section covers a few critical aspects of digital design that are important to understand. First, a methodology for creating frequency–dependent tabular transmission–line models is presented. The tabular format is a convenient way to model the frequency–dependent nature of the conductor and dielectrics described in Chapters 5 and 6. Next, the problem of nonideal current return paths is explored so that the engineer will understand how they affect signal integrity. Finally, the signal integrity impact of transitioning between layers using plated–through–hole vias is discussed.
10.1 CREATING A PHYSICAL TRANSMISSION-LINE MODEL
Digital design is typically performed using circuit simulators. Fortunately, most commercially available tools have transmission–line models that can be integrated with the digital circuitry to perform ...
