# Signal Integrity Issues  and Printed Circuit Board Design

## Douglas Brooks

#### 1.    Electronic Concepts

This introductory chapters covers the basic concepts of charge, voltage, and current, and DC vs. AC signals. Also covered are frequency and rise/fall time and ways they are measured. Fourier's Theorem is explained along with its relevance to signal harmonics.

#### 2.    Propagation Times

Propagation speed and time are covered, as well as the influence that trace configuration and structure (especially microstrip) can have on them. Wavelength and circuit timing issues are covered here, also.

#### 3.    Electrical Components

People who don't know what capacitors or inductors are, and how they effect current flow will find this chapter especially valuable. Easily understandable hydraulic analogs (like a garden hose) are used to help explain the concepts.

#### 4.    Voltage and Current Changes and Time Constants

Capacitors and inductors have very unique characteristics when faced with changing currents and/or voltages. This chapter covers those in detail. Then the chapter explains what RC and L/R time constants are and why they (especially RC) are so important in our circuits.

#### 5.    Resistance

Provides a thorough coverage of resistance circuits, including Kirchhoff's Laws, series and parallel combinations, power, and both Thevenin and Norton equivalent circuits.

#### 6.    Reactance

The resistance to current flow caused by capacitors and inductors is called "reactance." Finally, here, we get into AC circuits and how capacitors and inductors "impede" AC current flow. Series and parallel LC circuits are covered and the VERY important concept of resonance is covered here.

#### 7.    Impedance and Phase Shift

Finally, resistors, capacitors, and inductors all come together to form AC impedance. This chapter covers impedance: what it is, how to calculate and visualize it, and then what phase shift is all about.

#### 8.    Signal Integrity Overview

An overview chapter

#### 9.    EMI

Electromagnetic coupling is what EMI is all about. This chapter explains electromagnetic fields and coupling, describes the importance of loop areas, and then covers important PCB design rules to avoid or control EMI. Differential and common mode concepts are covered here in a way that is both complete but understandable to designers.

#### 10.    Reflections and Transmission Lines

Signals traveling down a trace reflect back. This may or may not be a problem in our circuits. If it may be a problem, we can control the reflections  by making our traces look like transmission lines and then terminating them correctly. That is what this chapter is all about. Termination techniques and design rules are covered in detail.

#### 11.    Some Transmission Line Simulations

A commercially available simulator is used as a tool to help the reader visualize what happens when transmission lines are terminated correctly and incorrectly.

#### 12.    Crosstalk

Crosstalk is really just a special case of EMI. Special care is taken to explain the difference between, and the effects of, forward and backward crosstalk, and then how to design our boards to control it. One way of eliminating both forward and backward crosstalk is presented.

#### 13.    Crosstalk Simulations

Crosstalk can be really hard to visualize. A commercially available simulator is used to illustrate the effects of crosstalk under various situations.

#### 14.    Differential Traces and Impedance

There is a lot of confusion about differential signals and traces; also between differential coupling and crosstalk (differential coupling is a special case of crosstalk, which is, itself, related to EMI). This chapter goes into these relationships, the problems of differential vs. common mode signals on our traces, and then the design rules we need to use if we are concerned about signal integrity issues with differential signals.

#### 15.    Bypass Caps and Decoupling Systems

There are two views regarding bypass decoupling capacitors today. One is the traditional view, the other approaches the issue from the power system impedance standpoint. This chapter explains the difference between those views, covers both of them, and then goes into depth about the role that ESR plays in decoupling.

#### 16.    Power Systems

We often use different, separated power supplies in our systems. This chapter explains some reasons why and how to deal with them.

#### 17.    Lossy Lines and Eye Diagrams

Most designers have not had experience with eye diagrams. The importance of eye diagrams is covered here, and then what happens to the "eye" when transmission line losses (skin effect and dielectric absorption) are introduced. Ways of compensating for these losses are introduced.

Appendices

#### A.    Square Wave Simulator

This appendix introduces a simulator that shows the underlying effect of the harmonic construction of a square wave.

#### B.    Why Inductors Induct

This is a popular part of Doug's seminar on basic electronics. By the time the reader finishes this appendix, he or she will understand electromagnets, motors and generators, transformers, and inductance, and how all these things are intimately related.

#### C.    Logarithms

A tutorial on logs.

#### D.    Phase Shift Simulation

This is an adjunct to Chapter 7, helping the reader actually play with circuit values and see the effects on voltages, currents, and phase shifts.

#### E.    Complex Algebra

A tutorial on complex algebra, imaginary numbers, and the concept of the square root of minus one!

#### F.    Transmission Line Simulation

UltraCAD has created a simulation tool for visualizing a waveform as it reflects back and forth along a trace under varying termination conditions. This appendix covers that tool and how to obtain it.

#### G.    Echo Illustration

The reader is informed how to obtain three audio files that illustrate a reflection illustration used in Chapter 10.

#### H. UltraCAD's Freeware Calculators

Descriptions of the freeware calculators UltraCAD has available for download.

#### I.    TDRs and VNAs

Many PCB designers have heard of these tools but don't know how they are used or what they can do. This appendix covers the basic theory behind these two very important analytical tools.

#### J.    Right Angle Corners

One of Doug's favorite topics. Read all about it here!

#### Glossary

118 terms that are used in our industry are explained in plain, easily understood English!