Digital Signal Processing Reference
In-Depth Information
10
TOPICS IN HIGH-SPEED CHANNEL
MODELING
10.1 Creating a physical transmission-line model
418
10.1.1 Tabular approach
418
10.1.2 Generating a tabular dielectric model
419
10.1.3 Generating a tabular conductor model
420
10.2 NonIdeal return paths
422
10.2.1 Path of least impedance
422
10.2.2 Transmission line routed over a gap in the reference plane
423
10.2.3 Summary
434
10.3 Vias
434
10.3.1 Via resonance
434
10.3.2 Plane radiation losses
437
10.3.3 Parallel-plate waveguide
439
References
441
Problems
442
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 method-
ology for creating frequency-dependent tabular transmission-line models is pre-
sented. 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.
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