Title: Transmission Lines in Digital and Analog Electronic Systems—Signal Integrity and Crosstalk
Author: Clayton R. Paul
Publisher: John Wiley, 2010
Today, clock and data speeds have moved into the gigahertz range. As the demand for faster data processing continues to escalate, these speeds will no doubt continue to increase. In addition, analog communication frequencies have also moved steadily into the gigahertz range. Although the physical dimensions of the signal’s interconnection and the PCBs supporting them have not changed significantly over these intervening years, the spectral content of the signals they carry has increased. Because of this, the electrical dimensions (in wavelengths) of the interconnections have a significant effect on the signals they are carrying; thus, getting the systems to work properly has become a major design problem. As many of us know very well, this scenario has generated a new design problem, referred to as Signal Integrity (SI). Good signal integrity means that the interconnect conductors should not adversely affect the operation of the modules that the conductors interconnect and most interconnect conductors must now be treated as distributed-circuit transmission lines.
This very new book of Professor Clayton R. Paul is intended as a textbook for a senior/first-year graduate-level course on transmission lines in electrical engineering (EE) and computer engineering (CpE) curricula. It is, in my opinion, also essential for industry professionals as a compact review of transmission-line fundamentals that is very well oriented and focused on the SI world.
The book has six chapters, divided in two main parts, plus one appendix for a total of 298 pages. A CD is included with the book and contains:
- Several computer programs described and used in the book for computing the per-unit-length parameter matrices
- A computer program for the automatic generation of sub circuit models for three-conductor lines
- Two MATLAB programs for computing the Fourier components of a digital waveform
- Two versions of PSPICE
Part I contains two chapters covering two-conductor transmission lines and designing for signal integrity. Chapter 1 gives the fundamental concepts of waves, wavelength, time delay, and electrical dimensions. In addition, the bandwidth of digital signals and its relation to pulse rise and fall times is discussed. A preliminary overview of the electromagnetic phenomena associated with signal integrity and crosstalk is also given.
Chapter 2 covers the time-domain analysis of those transmission lines. The transmission-line equations are derived and solved, and the important concept of characteristic impedance is covered. The important per-unit-length parameters of inductance and capacitance that distinguish one line from another are obtained for typical lines. The terminal voltages and currents of lines with various source waveforms and resistive terminations are computed by hand via wave tracing. This gives considerable insight into the general behavior of transmission lines in terms of forward- and backward-traveling waves and their reflections. The SPICE computer program and its personal computer version, PSPICE, contain an exact model for a two-conductor lossless line and are discussed as a computational aid in solving for transmission-line terminal voltages and currents. SPICE is an important computational tool since it provides a determination of the terminal voltages and currents for practical linear and nonlinear terminations such as CMOS and bipolar devices, for which hand analysis is very formidable. Matching schemes for achieving signal integrity are covered, as are the effects of line discontinuities.
Chapter 3 covers the corresponding analysis in the frequency domain. The important analog concepts of input impedance to the line, VSWR and the Smith chart (which provides considerable insight), are also discussed. The effect of line losses, including skin effect in the line conductors and dielectric losses in the surrounding dielectric, are addressed in this chapter. They are becoming increasingly critical and their detrimental effects are discussed.
Part II repeats these topics for three-conductor lines in terms of the crosstalk between transmission lines. In Chapter 4, the transmission-line equations for three conductor lossless lines are derived, and the important per-unit-length matrices of the inductance and capacitance of the lines are reviewed. Numerical methods for computing the per-unit-length parameter matrices of inductance and capacitance are studied, and computer programs are given that compute these numerically for ribbon cables and various structures commonly found on PCBs. Chapter 5 covers the solution of three-conductor lossless lines via mode decoupling. A SPICE sub circuit model is determined via this decoupling and implemented in the computer program SPICEMTL.EXE offered in the CD. This program performs the tedious diagonalization of the per-unit-length parameter matrices and gives as output a SPICE sub circuit for modeling lossless coupled lines. As in the case of two-conductor lines, this allows the study of line responses not only for resistive loads but, more importantly for SI purposes, nonlinear and/or reactive loads such as CMOS and bipolar devices that are common line terminations in today’s digital systems. How to incorporate the frequency-dependent losses of the line conductors and the surrounding dielectric into a solution for the crosstalk voltages is discussed in Chapter 6. The frequency-domain solution of the MTL equations is again given in terms of similarity transformations in the frequency domain. The time-domain solution for the crosstalk voltages is obtained in terms of the frequency-domain transfer function, which is obtained by superimposing the responses to the Fourier components of Vs(t).
The appendix gives a brief tutorial of SPICE (PSPICE), which is used extensively throughout the book.
In conclusion, I wish to quote the author, Professor Paul: “It does little good to write sophisticated software if the hardware is unable to process the instructions.” This technological problem will increase as the speeds and frequencies of the digital and analog systems continue to increase, seemingly without limit. This book is a significant contribution to correct that basic deficiency. EMC
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