PCB Signal Integrity                                                                        



Outline                                                                       Chapter*        


0.                 Introduction (video)                                                                 

Lesson 1    Review Background Information                                1 and 2           

Lesson 2    Eliminate Reflections                                                   17       

Lesson 3    Minimize EMI and Crosstalk Coupling                       18       

Lesson 4    Design Differential Traces                                           17.9    

Lesson 5    Solve Power Distribution Problems                           19       

Lesson 6    Understand High Frequency Resistance Losses     20       

Lesson 7    Deal with Really Short Wavelengths                          21       

Lesson 8    Control Trace Temperatures                                       16       

Lesson 9    Final Thoughts                                                             22       

00.              Summary (video)                                                                                  

                                                                        *  Lessons correlate with this chapter in PCB Currents        

                                                                                                Lessons 2 through 7 also correlate loosely with chapter 22


Lesson 1 Review Background Information                                                                              

            1.1 Gain Historical Perspective                                                            

            1.2 Understand the Nature of Current                                                               

            1.3 Understand Frequency                                                                   

            1.4 Visualize Electromagnetic Fields                                                               

            1.5 Deal with Propagation Speed                                                                     

            1.6 Understand Impedance                                                                  


Lesson 2 Eliminate Reflections                                                                                   

            2.1 Understand Reflections                                                                  

            2.2 Implement the CI Solution                                                             

            2.3 Avoid CI Pitfalls                                                                 


Lesson 3 Minimize EMI and Crosstalk Coupling                                                                                 

            3.1 Understand EMI and Crosstalk                                                                   

            3.2 Route for Minimum Coupling                                                                    


Lesson 4 Design Differential Traces                                                                            

            4.1 Compare single-ended and differential traces                                                                    

4.2 Understand differential impedance                                                            

            4.3 Avoid differential trace pitfalls                                                                   


Lesson 5 Solve Power Distribution Problems                                                                         

            5.1 Understand PDS Problem                                                              

            5.2 Compare Traditional and Impedance Solutions                                                                 


Lesson 6 Understand High Frequency Resistance Losses                                                                   

6.1 Learn About Skin Effect                                                                 

            6.2 Learn MORE about Skin Effect                                                                   

            6.3 Learn About Dielectric Losses                                                                   

            6.4 Deal With Lossy Transmission Lines                                                                     


Lesson 7 Deal with Really Short Wavelengths                                                                         

            7.1 Learn Some Design Techniques When Wavelengths are Really Short                                                                    


Lesson 8 Control Trace Temperatures                                                                         

            8.1 Design Traces For Temperature                                                                 

            8.2 Design Traces For Melting Point    


Lesson 9 Final Thoughts                                                         


Expanded Outline:


Lesson 1: “Review Background Information” covers several basic background topics particularly helpful in understanding the following material. Doug first puts PCB signal integrity issues into an historical perspective, showing how the progression of the various topics relates to faster and faster rise times. He then reviews the basic topics of the nature of current, frequency, rise time, harmonics, and impedance. Two lessons emphasize the importance of some of the basic laws of electronics, and the nature of electromagnetic fields.


Lesson 2: “Eliminate Reflections” introduces the problem of reflections. This problem is solved with transmission lines, or “controlled impedance traces.” But this solution is not sufficient, since terminations also play an important role.


Lesson 3:  “Minimize EMI and Crosstalk Coupling” describes these two effects and their importance to PCB designers. In explaining crosstalk Doug utilizes several creative animations. In Lesson 3.2 Doug shows how it is possible to route two very long traces very close together without any crosstalk at all at the far end of the “victim” trace, and demonstrates that with the results of simulations.


Lesson 4: “Design Differential Traces” introduces the concept of differential signals and why they might perform better than single-ended signals. But differential traces require their own set of design guidelines. Doug outlines what these are, and why he believes in the guidelines he proposes.



Lesson 5: “Solve Power Distribution Problems” discusses the problems we might have in making power available around our boards. The two most common problems are (a) making sure there is enough charge available at the time and point of switching, and (b) making sure that “ground bounce” doesn’t negatively impact the signal. The solution to these problems involves bypass capacitors. But then Doug discusses the questions of how many, what size, where to put them, why, and the role ESR plays in all of this.


Lesson 6: “Understand High Frequency Resistance Losses” introduces the idea that resistance might not be constant with frequency. At least it might look that way. Doug introduces and explains the phenomena of skin effect and dielectric losses and how these ultimately result in lossy transmission lines. He then shows what we might be able to do about that.



Lesson 7: “Deal with Really Short Wavelengths” covers what happens when rise times get so short, and critical lengths get so short, that there is no physical room for implementing the solutions discussed in the previous lessons. At this stage, even via lengths might be longer than critical lengths. This severely limits what we can do with vias and how we should design them. Doug covers all this in this lesson.


Lesson 8:  “Control Trace Temperatures” covers the relationship between trace currents and temperatures. Traces must be sized carefully to carry their currents with acceptable temperature rise, and Doug covers why this is so, and then how to go about doing this. In the case where a catastrophic failure might severely overload a trace, Lesson 8.2 covers how to size a trace to last long enough to safely “shut down” the system after such a failure.


Lesson 9: “Final Thoughts” is just that, some concluding thoughts Doug wants to leave with you. These include a summary of what we have covered in the context of the historical evolution of signal integrity on PCBs, a summary of the important design rules introduced, Doug’s answer to the student who once asked “Why should we believe your design rules?”, and Doug’s response to those who forecast the coming “death” of the PCB.