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PCB Currents: How They Flow, How They React

Book Description

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.

Table of Contents

  1. About This eBook
  2. Title Page
  3. Copyright Page
  4. Dedication Page
  5. Contents
  6. Preface
    1. Focus
    2. Organization
    3. Target Audience
  7. Acknowledgments
  8. About the Author
  9. Part I: The Nature of Current
    1. 1. Electrons and Charges
      1. 1.1. The Flow of Electrons
      2. 1.2. Atomic Structure
      3. 1.3. Insulators
      4. 1.4. Charge Field
      5. 1.5. Magnetic Field
      6. 1.6. Forces Driving Current
      7. 1.7. Voltage versus Current
      8. 1.8. Direction of Current Flow
      9. 1.9. Semiconductor Hole Flow
    2. 2. Basic Current Concepts
      1. 2.1. Types of Current
      2. 2.2. Propagation Speeds
      3. 2.3. Circuit Timing Issues
      4. 2.4. Measures of Current
      5. 2.5. Measurement Techniques
      6. 2.6. Thermal Noise and Current Thresholds
    3. 3. Basic Current Laws
      1. 3.1. Flows in a Loop
      2. 3.2. Current Is Constant Everywhere in a Loop
      3. 3.3. Ohm’s Law
      4. 3.4. Kirchhoff’s First Law
      5. 3.5. Kirchhoff’s Second Law
  10. Part II: Current Flow in Basic Circuits
    1. 4. Resistive Circuits
      1. 4.1. Resistivity
      2. 4.2. Resistive Current and Phase
      3. 4.3. Series Resistors
      4. 4.4. Parallel Resistors
      5. 4.5. Power and Energy
      6. 4.6. Resistive Voltage Divider
    2. 5. Reactive Circuits: Capacitors and Capacitance
      1. 5.1. The Nature of Capacitance
      2. 5.2. Definition of Capacitance
      3. 5.3. Current “through” a Capacitor
      4. 5.4. AC Current “through” a Capacitor
      5. 5.5. Displacement Current
      6. 5.6. Ohm’s Law for Capacitance
      7. 5.7. Plot of Capacitive Reactance versus Frequency
      8. 5.8. Phase Shift for Capacitance
      9. 5.9. How Capacitors Combine
      10. 5.10. Power Dissipated in a Capacitor
      11. 5.11. Formula for Capacitance
    3. 6. Reactive Circuits: Inductors and Inductance
      1. 6.1. The Nature of Inductance
      2. 6.2. Definition of Inductance
      3. 6.3. DC Current “through” an Inductor
      4. 6.4. AC Current “through” an Inductor
      5. 6.5. Ohm’s Law for Inductance
      6. 6.6. Plot of Inductive Reactance versus Frequency
      7. 6.7. Phase Shift for Inductance
      8. 6.8. How Inductors Combine
      9. 6.9. Power Dissipated in an Inductor
      10. 6.10. General Equation for Inductance
      11. 6.11. Skin Effect
    4. 7. Reactive Circuits: Resonance
      1. 7.1. Series Resonance
      2. 7.2. Parallel Resonance
    5. 8. Impedance
      1. 8.1. The Meaning of Impedance
      2. 8.2. Magnitude of Impedance
      3. 8.3. Impedance Phase
      4. 8.4. Series RLC Circuit Example
      5. 8.5. Parallel RLC Example
      6. 8.6. Power Factor
      7. 8.7. RLC Circuits at Resonance
      8. 8.8. Impact of R around Resonance
      9. 8.9. How Impedances Combine
    6. 9. Real Components and Parasitics
      1. 9.1. Resistors
      2. 9.2. Inductors
      3. 9.3. Capacitors
      4. 9.4. Coupling between Components
      5. 9.5. Self-Resonance
    7. 10. Time Constants and Filters
      1. 10.1. RC Time Constants
      2. 10.2. L/R Time Constants
      3. 10.3. RC Filters
      4. 10.4. Quality Factor, Q
    8. 11. Transformers
      1. 11.1. Magnetic Fields Revisited
      2. 11.2. Coupling Efficiency—Iron Cores
      3. 11.3. Coupling Efficiencies—Frequency Limits
      4. 11.4. Coupling Effect—Turns Ratios
      5. 11.5. Current and Impedance Ratios
      6. 11.6. Transformer Losses and Efficiency
      7. 11.7. Winding Polarity: Lenz’s Law
    9. 12. Differential Current Flow
      1. 12.1. Concepts
      2. 12.2. Some Illustrations
      3. 12.3. Differential and Common Modes (Odd and Even Modes)
      4. 12.4. Mode Shift or Conversion
    10. 13. Semiconductors
      1. 13.1. Electron Shells Revisited
      2. 13.2. Semiconductor Doping
      3. 13.3. Semiconductor Diode Junctions
      4. 13.4. Zener Diode
      5. 13.5. Current Flow through Diodes
      6. 13.6. Bipolar Transistors
      7. 13.7. Field Effect Transistors
  11. Part III: Voltage and Current Sources
    1. 14. Voltage and Current Sources
      1. 14.1. Fundamental Sources
      2. 14.2. Ideal Voltage and Current Sources
      3. 14.3. Equivalent Circuits
  12. Part IV: Current Flow on Circuit Boards
    1. 15. Where Do Currents Flow on Circuit Boards?
      1. 15.1. Signal Currents
      2. 15.2. Power Currents
      3. 15.3. Return Currents
    2. 16. Current and Trace Temperatures
      1. 16.1. Fundamental Concepts
      2. 16.2. Historical Background
      3. 16.3. Relationships
      4. 16.4. Fusing Currents
    3. 17. Current Reflections
      1. 17.1. A Proposition
      2. 17.2. The Fundamental Issue
      3. 17.3. Critical Length
      4. 17.4. Transmission Lines
      5. 17.5. Terminations
      6. 17.6. Reflection Coefficients
      7. 17.7. How Coupling Impacts Impedance
      8. 17.8. How Currents Flow
      9. 17.9. How Differential Currents Flow
    4. 18. Coupled Currents/EMI/Crosstalk
      1. 18.1. Basic Concepts
      2. 18.2. Antennas
      3. 18.3. EMI
      4. 18.4. Crosstalk
    5. 19. Current Distribution and Bypass Capacitors
      1. 19.1. Nature of the Problem
      2. 19.2. The Traditional Approach
      3. 19.3. Power Distribution Impedance Approach
      4. 19.4. Which Approach?
    6. 20. Frequency-Variable Resistance and Lossy Transmission Lines
      1. 20.1. Skin Effect
      2. 20.2. Dielectric Losses
      3. 20.3. Lossy Transmission Lines
    7. 21. Currents and Vias
      1. 21.1. Power Dissipation in Vias
      2. 21.2. Via Inductance
      3. 21.3. Via Characteristic Impedance
      4. 21.4. Reflections within Vias
      5. 21.5. Blind and Buried Vias
    8. 22. Current and Signal Integrity
      1. 22.1. Historical Perspective
      2. 22.2. PCB Design Rules
      3. 22.3. Differential Trace Design Rules
      4. 22.4. Via Design Rules
      5. 22.5. Why Should You Believe These Design Rules?
  13. Appendices
    1. A. Current Flow and Maxwell
    2. B. Eye Diagrams
    3. C. Coming Death of the Circuit Board
  14. Index