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PCB Currents

PCB Currents

How They Flow, How They React (Paperback)

Douglas Brooks

Feb 2018, Paperback, 348 pages
ISBN13: 9780134878478
ISBN10: 0134878477
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The Plain-English Guide to Electronics and Current Flow for Every PCB Designer


Today, PCB designers must deal with issues such as crosstalk and EMI-–issues that were once associated only with components. This requires electronics knowledge that many PCB designers never gain through formal training. In PCB Currents, renowned PCB designer Douglas Brooks teaches these essentials descriptively, in plain English, with as little reliance on mathematics as possible. Building on his widely praised seminars, Brooks explains what current is, how it flows, and how it reacts. He begins by reviewing the nature of current, and then explains current flow in basic circuits, discusses sources that supply and drive current, and addresses the unique problems associated with current on PCBs. Brooks concludes by thoroughly illuminating signal integrity issues caused by current flow. He offers practical design solutions for each common type of problem, as well as for complex challenges involving very high frequency harmonics and very short wavelengths.


Coverage includes

• Current: its fundamental nature, basic definitions, and key concepts

• Five fundamental laws of current, including Kirchoff’s law and Ohm’s law

• Basic circuit concepts: resistive circuits, reactive circuits, and impedance

• Voltage and current sources: Where electrons come from and why they move

• Current-related PCB issues: temperature, transmission lines, reflections, coupled currents, power distribution, skin effect, dielectric losses, and vias

• Solutions for signal integrity issues caused by current flow, from on-board inductance and apparent resistance changes to more complex problems


The text is written to be accessible and valuable for PCB designers at all levels of experience, whether they have engineering training or not.

Preface ix

Part I: Nature of Current 1

Chapter 1: Electrons and Charges 3

Chapter 2: Basic Current Concepts 19

Chapter 3: Basic Current Laws 57


Part II Current Flow In Basic Circuits 65


Chapter 4: Resistive Circuits 67

Chapter 5: Reactive Circuits: Capacitors and Capacitance 77

Chapter 6: Reactive Circuits: Inductors and Inductance 91

Chapter 7: Reactive Circuits: Resonance 105

Chapter 8: Impedance 113

Chapter 9: Real Components and Parasitics 133

Chapter 10: Time Constants and Filters 143

Chapter 11: Transformers 159

Chapter 12: Differential Current Flow 173

Chapter 13: Semiconductors 181

Part III: Voltage and Current Sources 193

Chapter14: Voltage and Current Sources 195

Part IV: Current Flow On Circuit Boards 199

Chapter 15: Where Do Currents Flow on Circuit Boards 201

Chapter 16: Current and Trace Temperatures 205

Chapter 17: Current Reflections 213

Chapter 18: Coupled Currents/EMI/Crosstalk 233

Chapter 19: Current Distribution and Bypass Capacitors 249

Chapter 20: Frequency-Variable Resistance and Lossy Transmission Lines 263

Chapter 21: Currents and Vias 275

Chapter 22: Current and Signal Integrity 285

Appendices: 301

Appendix A:Current flow and Maxwell 303

Appendix B: Eye diagrams 307

Appendix C: Death of the Circuit Board 311

Index 313

  • Covers crucial electrical engineering aspects of board design that are difficult for new board designers to learn elsewhere
  • Comprehensive: from basic current definitions and electronics laws to complex signal integrity issues
  • Free Transmission Line Simulator helps engineers visualize signal behavior at the end of a transmission line
  • Written in plain English, with minimal use of complex formulas
  • By one of the field’s leading experts and most respected authors

Douglas Brooks has a B.S./E.E. and an M.S./E.E. from Stanford University and a Ph.D. from the University of Washington. He has had forty years of experience in the electronics industry, ranging from circuit design engineer on the space program to president of his own manufacturing company. For the past twenty years he has been president of UltraCAD Design, Inc., a premier PCB Design Service Bureau in the Pacific Northwest.

Brooks has published hundreds of articles during his career. In the last twenty years, these articles have appeared in PCB Design Magazine, on Iconnect007’s websites, on Mentor Graphics’ web pages, and on UltraCAD’s web pages. In 2003, he published the book Signal Integrity Issues and Printed Circuit Board Design (Prentice Hall).

Brooks served on the faculty of San Diego State University for three years and was a visiting associate professor at the University of Washington for one year. He has given numerous seminars on Signal Integrity Issues in PCB Design over the past fifteen years all over the United States and in Moscow, Beijing and Shanghai, Taiwan, Japan, and Australia.

Brooks finally retired in 2012.