ECTROMAGNETIC COMPIILITY HANDBOOK

Transcription

1 ECTROMAGNETIC COMPIILITY HANDBOOK KENNETH L KAISER CRC PRESS Boca Raton London New York Washington, D.C.

2 Contents EMI Sources 1.1 Industrial Noise Sources Office Noise Sources Residential Noise Sources ' Holiday Noise Sources Natural Noise Sources Automobile Noise Sources RF Electromagnetic Sources in the Spectrum Noise, Interference, and Unwanted Signals 1-2 Decibel and Approximations 2.1 RMS vs. Maximum Amplitude Relative Decibels Electric Field, Magnetic Field, and Power Density db Conversions Adding db to dbm Adding db to dbmv Adding db to dbma Negative db Significance of 3 db and 5 db Significance of 6 db and 10 db Is db Power or Voltage Gain? db Version of Equations db Multiplication Adding dbmv to dbmv db Approximations Signal Sources and Unmatched Loads Common Approximations 2-11 Electrical Length 3.1 Electrical Length vs. Physical Length Standing Waves Antenna Effects and Effective Permittivity Unshielded Conductor Radiation PCB Trace Radiation Electrically-Large Car Properties of Electrically-Small Metallic Objects 3-6 xiii

3 Fast Bode Magnitude Plotting 4.1 Quickly Sketching a Bode Plot A Real Function i The Spectrum of Common Functions Equations for the Spectral Magnitude Expression from the Bode Plot Common Improper Standard Forms The Other Bode Plot: The Phase Plot 4-21 Skin Depth, Wire Impedance, and Nonideal Resistors 5.1 Eddy's Currents : The Value of a dc Resistance Measurement..' Skin Depth for Round Wires Rectangular vs. Circular Wires High-Frequency Resistance Formula Importance of the Skin Depth when 8> r w and Litz Wire '.. ' ' Inductance Dominating over Resistance Wire Gauge and Cross-Sectional Area Importance of Skin Depth in House Wiring :." Stranded and Solid Wire ::..'...'...;? Aluminum Wire in a House.'!.' When is the Internal Inductance Important? '.'..... : Adjusting a Transformer Tap to Compensate for Line Drop '...' Power Loss in Speaker Wire ;....*..: Impedance of a Grounding Jumper Wire.../.....:. : The Resonance of a Resistor...:...v...: Resistor Acting Like a Capacitor or an Inductor..!...! Resistors without an Impedance Peak..'..?:'..'.; A Resistor Cage :.v. : ;. :... ;.'.V...'.' Resistor Types.':.:..'.....' Exotic Audio System Interconnect Cablev. ;...;'...:...:.'.$.[.'. _..'..'. \:h i Nonideal Capacitors and Inductors, Realistic Range of Impedances,..,,..., Model of a Practical Capacitor Model of a Practical Inductor, ( Resonant Frequency of a Practical Capacitor '.. ' Resonant Frequency of a Practical Inductor, Resistive Region of a Capacitor, Resistive Region of an Inductor ESR Determination ' Maximum Q of an Iron-Core Inductor Why Place Two Different Capacitors in Parallel? ' XIV

4 6.11 Capacitor Types Choosing the Right Capacitor Inductor Types Impedance Summary Passive Filters 7.1 Filters Low-Pass Capacitor Filter High-Pass Capacitor Filter Low-Pass Inductor Filter High-Pass Inductor Filter Low-Pass RC Filter Low-Pass LC Filter Low-Pass CL Filter High-Pass LC and CL Filters Series Band-Pass Filter Shunt Band-Pass Filter Band-Reject Filters Low-Pass it Filter High-Pass 7t Filter Low-Pass T Filter High-Pass T Filter Filter Comparisons RC Filter Comparisons More RC Filters Maximum Possible Q High-Q Circuit Conversions Q Selection for Filters Series and Parallel RLC Circuit Properties Measuring the Q of a Crystal Distorting a Signal Passive vs. Active Filters Insertion Loss Insertion Loss and Q Filtering at High-impedance Levels Filtering on A/2 Transmission Lines Impedance "Matching" with Passive Filters Three-Terminal Capacitor Feed-Through Capacitor Cable Modeling 8.1 Purpose of a Cable High-Fidelity Speaker Wire Candidates 8-3 xv

5 8.3 Selecting the Cable Model Failure of the Lumped-Circuit Model Characteristic Impedance Characteristic Impedance of a dc Power Bus Reducing the Characteristic Impedance Influence of Dielectric Constant Coax and Twin-Lead Thinly Coated Twin-Lead Beads in Coax Dielectric Resistance and Insulators Cable Capacitance and Audio Cables Grounding Strap Impedance ESD Signal Wire Guideline TwistedPair When the Line Can Be Ignored Line Resonance Multiple Receiver Loading Proximity Effect Characteristic Impedance Formula 8-52 Transient Behavior in the Time Domain 9.1 Transient vs. Sinusoidal Steady State A Time-Delay Circuit An RC Integrator An RC Differentiator A More General RC Circuit Static Charge Buildup Current Surges and Capacitor Dividers Compensation, General Voltage Divider, and Multiple Capacitors Multiple-Supply RC Circuits RC Rise Time and Speed Measuring the Time Constant Energy and Power in RC Circuits The Inductive Kick RL vs. RC Differentiators and Integrators Inductive Load Switching, Release Time, and Rise Time dc Biasing an Inductor and Inductive Energy Inductive vs. Capacitive Circuits Series and Parallel RLC Circuits Ringing as a Function of Q Ringing and Resonant Frequency Digital Signal Ringing Effect of the Energy Content of the Input Signal on Ringing Oscillation Burst The Ringing Circuit 9-62 xvi

6 9.24 Shunt Peaking to Reduce the Rise Time Other Two Energy-Storage Element Circuits Double-.RC Lumped Interconnect Model Advanced RLC Circuit More Overshoot, Settling Time, and Ringing Frequency Air Breakdown 10.1 Breakdown Voltage Glows, Arcs, Coronas, and Sparks Nonuniform Fields and Time-Varying Arc Ideal Switching of Simple Loads Ideal Switching of Complex Loads Switching and Breakdown Showering Arc Speed of Switching Suppressing the Breakdown Switch Network Example Arc Suppression with Resistive Loads Arc Suppression with Capacitive Loads Arc Suppression with Inductive Loads Sparking at Very Low Voltages? Switch Corrosion and Erosion Maximum Electric Field and Breakdown Table Minimum Corona Voltage Voltage Rating of Coax Solutions to Poisson's Equation Arcing in a Silo All of the Electric Field Boundary Conditions Powder Bed The Field from Corona Transient Behavior in the Frequency Domain 11.1 What Is the Laplace Transform? Properties of the Laplace Transform Massive Laplace Transform Table The Step Function The Impulse Function The Impulse Response, Step Response, and Transfer Function Modeling a Real Inductor Using a Current Ramp Sinusoidal Steady State with Transforms Initial Capacitor Voltages and Initial Inductor Currents Voltage Zapper Blimp Amplitude xvii

7 11.12 Audio Filter Response Half-Wave Rectifier The Power of the Laplace Transform Spectra of Periodic and Aperiodic Signals 12.1 Time and Frequency Viewpoints and Periodicity The Marvelous Fourier Series Fourier Series Forms for Periodic Signals and their Spectra Success of the Fourier Series Approximation Fourier Series Table Converting between the Various Fourier Forms Using the Table to Determine Other Series Last Resort: Using the Definition to Determine the Fourier Series Fourier Series Shortcuts via Symmetry Circuit Analysis Using the Fourier Series Amplitude Spectrum of a Digital Waveform X Guideline for Digital Waveforms Doubling the Frequency and Halving the Rise Time Fourier and Laplace Transforms Necessary Tools for Understanding Aperiodic Signals Obtaining the Fourier Transform via Properties, the Laplace Transform, and the Fourier Series Spectrums of Aperiodic Signals Smoothness and Amplitude Spectrum Highest Frequency of Interest of a Digital Waveform Double-Exponential Pulse Modeling a Stroke of Lightning Spectrum of Double-Exponential Pulse Energy in a Double-Exponential Pulse Using Just the Rise Time Many Delay and Rise Times Effective Rise Time of Systems in Cascade Impulse Responses of Many Systems in Cascade Many Bandwidths Time-Bandwidth Product Consequence of Ripple in the Frequency Domain Frequency-Domain or Time-Domain Testing? Transmission Lines and Matching 13.1 Voltage Reflection and Transmission Coefficients Impedance Mismatch VSWRandSWR The Cost of a VSWR > xvin

8 13.5 Distinguishing between the Load and Source Transient and Steady-State Input Impedance Transient Reflections Matching at the Receiver and its Cost Shunt Matching with Distributed Receivers Microstrip Branching Shunt Diode Matching Shunt RC Matching Matching at the Driver and its Cost Series Matching with Multiple Receivers Effects of Nonzero Source and Load Reflection Coefficients Signal Bounce as a Function of Time Settling Time Settling Time vs. Reflection Coefficient Receiver Voltage when Rise Time = Line Delay Receiver Voltage when Rise Time «Line Delay Receiver Voltage when Rise Time» Line Delay Advanced Transient Problem Ringing in Lumped Circuits More Shunt Matching Shunt Matching with a Split Termination for a TTL System Shunt Matching with a Split Termination for a CMOS System Shunt Matching with a Split Termination for an ECL System Split-Termination Equivalent Experimentally Determining the Line Impedance Series Matching and Dynamic Output Resistance Driver Current for Series and Shunt Matching Summary of Matching Methods Relationship Between Sinusoidal Input and Output Voltage The Sinusoidal Current Expression The Sinusoidal Input Impedance Coaxial Cable Branching "Y" Splitter for "Hair-Ball" Networks Stub Tuning Inductive Loading Low-Loss Lines and Short Lines Inductive Line Capacitive Line The Lossy Expressions for Sinusoidal Steady-State Telephone Lines and the "RC" Region Transmission Line Parameter Expressions S Parameters Using the Sinusoidal Reflection Coefficient for Transient Problems Effect of Receiver Capacitance on Transient Behavior

9 13.49 Complete Reflection due to Excessive Capacitance Amplitude of Mismatch "Blimp" from Receiver Capacitance When not to Match! Passive Contact Probes 14.1 Low-Impedance Passive Probe Improved Model of the Low-Impedance Passive Probe Operating Range of the Low-Impedance Passive Probe Improved Model of the Cable and Scope High-Impedance Passive Probe Input Impedance of a High-Impedance Passive Probe High-Impedance Probe Compensator Testing with a Square Wave Effect of Inductance on the Probe Inductance, Magnetic Coupling, and Transformers 15.1 Inductance Equivalent Inductance Winding Direction and the Dot Convention Modeling the Inductance of Two Parallel Strips Modeling the Inductance of a Loop Near a Wire Changing Inductance via Magnetic Coupling Different Currents but Identical Voltages Useful Properties of Parallel Inductors Grounding Strap Inductance Multiple Conductor Grounding Straps Reducing PCB Land Inductance Typical Mutual Inductance of Wire Lead Position on Capacitors The Many Inductances and the "Sniffer" Optimum Loop Dimensions Pickup Loop Loading Down the Circuit Inductance Formula Ideal Transformers Operating in Sinusoidal Steady State Typical Ideal Transformer Problems RF Tuning Behavior of a Nonideal Transformer Linear Transformer Models Low-Frequency Model Mid-Frequency and Power-Frequency Models High-Frequency Model Wideband Models Multiwinding and Tapped Transformers 15-90

10 15.28 Placing Transformers in Series and Parallel Hybrid Transformers Autotransformers Transformer Ratings Nonlinear In-Rush Current Instrument Transformers Tuned Transformers Some "Other" Transformers Determining All of the Unknowns Transient Inputs to Linear Transformers Step Input to a Real Step-Up Transformer Step Input to a Real Step-Down Transformer When Are Transformers Used? Magnetic Materials and a Few Devices 16.1 B = uh Magnetic Circuits Toroidvs. Rod Common-Mode Choke Ringing and Chokes Increasing Inductance with a Bead Relationship between Bead Parameters and Inductance Saturating Ferrite Beads How Ferrite Filters Work Loss Factor The Hysteresis Curve and the many Permeabilities Further Discussion of the Hysteresis Curve Hard vs. Soft Survey of Typical Magnetic Properties Demagnetization Field and Magnetic Charge Purpose of the Air Gap Force, Torque, and Magnetization Current Free Energy from a Magnet? Baluns and Balanced Circuits 17.1 Definition of Balanced System Voltage Balun Another Voltage Balun Current Balun Another Current Balun Why Baluns Do Not Always Work Another Common-Mode Choke Limitation and Shielding a Choke Varying Common-Mode Impedance xxi

11 17.9 Excess Cable Location of Choke Multiple Cores Why a System Is Never Truly Balanced Balancing and Common-Mode Currents A Resistive Balanced Circuit The Conversion Process CMRR Balanced Input Receivers Balanced Output Drivers Balanced and Single-Ended Drivers and Receivers Balanced and Matched Common Choke Ferrite Beads Grounding Coax Outside a House Isolation Transformers Single, Double, and Triple Transformer Shielding Optoisolators Common-Mode and Differential-Mode Impedance Transmission Line Baluns Matching n and O Pads Matching T and H Pads Matching L and U Pads Bridged T and H Pads Low-Impedance and High-Attenuation Pads Cable Shielding and Crosstalk 18.1 Best Cable to Reduce Magnetic Noise Connecting Balanced and Unbalanced Systems Bicoaxial Line Reducing Noise Through Transformers Modeling a Cable as a Transformer Break Frequency of Coax Multiple Grounding Points for Coax Keeping Noise off the Shield Switching the Neutral and Hot Wires Avoiding Ground Loops and Hum Multipoint and Hybrid Grounding Dynamic Range Between Systems Multiple Returns in Ribbon Cable Loose Wires as a Cable Transfer Impedance Loss Impedances and Transfer Admittance The Coupling Model xxii

12 18.18 Pigtails and Connectors Weak Links in a System Capacitive or Inductive Crosstalk? Measurement Tools Susceptibility of High and Low Resistances Susceptibility of Scopes Foam Encapsulation Inductive Crosstalk and the 3-W Guideline Capacitive Crosstalk and the 3-W Guideline Long Lines vs. Close Lines " Guideline for Telephone Lines Four-Conductor Trace Layout Q Guideline Why Twisting Often Helps RC Circuit and Crosstalk Summary of Methods to Reduce Crosstalk Fiber's Weakness Radiated Emissions and Susceptibility 19.1 Radiated or Conducted Vehicle Interference? The Automobile Noise Mystery Copper Plane Addition Emissions from Twin-Lead Line Differential-Mode Current Emissions from Twin-Lead Line Common-Mode Current Emissions from Twin-Lead Line Reducing Emission Levels Susceptibility of Twin-Lead Line Small-Loop and Hertzian Dipole Models Neglecting the Capacitance and Inductance Probe Lead Pickup Wave Equation Susceptibility of Electrically-Long Twin-Lead Line Susceptibility of Electrically-Long Wire Above a Ground Plane Theory of Current Probes Loaded Current Probe Transfer Impedance of Current Probes Conducted Emissions and Susceptibility 20.1 Polluted Power Line Locating Malicious Conducted Interference Suppressors LISN's Input Impedance of LISN Maximum Input Impedance of a Network xxiii

13 20.7 Resonance of LISN with Capacitive and Inductive Loading Separating the Common and Differential Common-Mode and Differential-Mode Filters Nonlinear Evils Plane Wave Shielding 21.1 The "Magic" of Shielding Waves Revealed The Impedance of a Wave Impedance of Air, Real Metals, and Real Insulators Reflection and Transmission Coefficients Plane Wave Power Single-Layer Conducting Shield Thin Shields and Reflection Loss Thick Shields and Absorption Loss Skin Depth Skin Depth for Good Insulators Skin Depth for Several Good Metals Complex Permittivity and RF Through Human Fat Microwaves through Human Fat Table of Dielectric Constants and Loss Tangents Loss in db Per Skin Depth Reflection, Absorption, and Multiple-Reflection Losses Effect of Dielectric Constant on Shielding Near Field or Far Field? Wave Impedance Electric Field Shielding 22.1 The "Magic" of Electric Field Shielding Revealed Size is Important! Shielding Reciprocity? Using Capacitance to Model Shielding Capacitor Shielding Three-Terminal Capacitor Shielding Cans Finite-Conductivity Spherical Bodies Step Response of Spherical Bodies Finite-Conductivity Cylindrical Body Electric Blankets and Infants Typical Electric Field Strengths Current Through and Voltage Across a Field-Immersed Person Insulating Spherical Shields Insulating Cylindrical Shields EQS and Perfect Conductors xxiv

14 23 Magnetic Field Shielding 23.1 The "Magic" of Magnetic Field Shielding Revealed Magnetic Field from Simple Current Distributions Magnetic Fields for Other Current Distributions Magnetic Field Boundary Conditions Flux Shunting Explained via Boundary Conditions Self Shielding Nature of Coax Method of Images for Currents Wire Partners Can Reduce Fields Thick Poor Conductors Thin Good Conductors Spherical and Cylindrical Conducting and Magnetic Shields Pure Magnetic Spherical Shell Pure Magnetic Cylindrical Shell Finite-Length Cylindrical Shell Shielding the Source and Shielding Reciprocity Shielding a Cosmetologist with a Body Suit Power Line Shielding via Burying Wave Impedance Concept Flat Shielding of Current-Carrying Loops Grounding Shields Cheap Shielding Nonideal Shapes Reducing the Magnetic Coupling Between Inductors Typical Magnetic Flux Densities MQS and Perfect Conductors Decoupled Time-Varying Electric and Magnetic Fields Additional Shielding Concepts 24.1 When Is a Shield Flat? Performance of a Shielded Room Laminated Shields Shields with an Air Gap Gold Coating on Glass Laminates for Magnetic Fields Rust Never Sleeps Corrosion Surface Impedance Voltage and Current along a Chassis Impedance of Coated Conductors Nontraditional Shielding Materials Shielding Effectiveness vs. Surface Resistance Near-Field Electric Shielding Effectiveness An Equipotential Surface Electric vs. Magnetic Field Measurements XXV

15 24.16 Single-Conductor Transmission Line TEM, TE, and TM Waves Cutoff Frequency of a Waveguide Attenuation Beyond Cutoff Seepage through a Seam One Large Hole vs. Several Smaller Holes Honeycomb Ventilation Openings Coupling through an Aperture Radio in a Metal Box Lightning Protection Inside an Automobile Test Chambers 25.1 Cage Antenna Screen Rooms and OATS's Resonant Frequency of a Midsize Car and Notebook Computer High or Low Q? Abundance of Modes and Mode Degeneracy Stirring Up the Fields Dark Room TEM Cell Floating Metal and Guard Electrodes 26.1 Examples of Floating Metal Unused Conductors To Ground or Not to Ground Nearby Metal Artificially Changing Capacitance and Inductance Loose Metal Arcing and Floating Metal Floating Inputs Tube vs. Transistor Multimeter The Powerless Voltage Standard Bridge Circuit Connection to a Floating Bridge Irrelevance of Floating a Shield Strain Gauge Shielding Electronically Reducing Capacitance The Guard Electrode Interference Control with a Guard Shield Electrostatic Discharge 27.1 What is ESD? Methods of Charging Triboelectric Series Microphony 27-7 xxvi

16 27.5 Voltage and Current Responses Sources of Current Rate of Charge Decay Maximum Surface Charge Before Breakdown Grounded Conducting Objects and Charged Insulating Surfaces Charge Accumulation Along Interfaces Convection Charge Flow Potential of an Insulator's Surface Electric Field from Simple Charge Distributions Electric Field From Other Charge Distributions Discharges Classified Minimum Ignition Energy Electrostatic Hazard Case Studies Measuring Charge Measuring the Electric Field Measuring Voltage Measuring Bulk and Surface Resistivity Maximum Body Voltage and Typical Capacitances RLC Discharge Model ESD Rules-of-Thumb and Guidelines Raindrop Bursts, P-Static, and Corona Noise Locating Weaknesses with a "Zapper" Surround, Ground, and Impound Wrist and Ankle Straps Floor Coatings Pink, Black, and Shielded Bags Static-Dissipative Work Surfaces Sugar Charge Decay Capacitance Measurement for Multiple Conductors Energy and Capacitance Capacitance Formula Grounding 28.1 Verbs, Nouns, and Adjectives Groundless Devices Ground Symbols A "Good" Ground Reference Reasons to Earth Ground Voltage Hazards Involving Ground Safe Current and Voltage Levels Transient Shocks Grounding the Neutral Wire in Service Panels GFIs IDCIs and the Achilles' Heel of GFCIs xxvii

17 28.12 Dangerous Two-Prong Devices Pigtail Adapters Safe Leakage Current for an Electric Razor Isolation Transformer Resistance Definition Resistance to Ground Formula L Guideline Surface Potentials When Lightning Hits The Purpose of Lightning Rods Rod Materials Measuring Earth's Resistivity Measuring the Resistance of an Earthing Electrode Three-Point Method Again Surge Impedance of an Electrode Dedicated Ground in a Plant Single-Point vs. Multiple-Point Grounding Circuit Board Layout for EMC 29.1 EMC Overview Immunity or Susceptibility? System Levels Introductory Component Layout Concepts Single-Layer PCB System Layout Single-Layer PCB Power Distribution System Multilayer Boards Board Resonance The Flow of Charge Down a Line Printed Circuit Board Trace Configurations Decoupling Capacitors More Decoupling Capacitors Antennas 30.1 Radiation Resistance Radiation Efficiency and Ohmic Losses Small Antennas Large Antennas Input Impedance Directive Gain, Directivity, and Power Gain Q and Bandwidth Receiving vs. Transmitting Antenna The Right Antenna Wave Orientation xxvm

18 30.11 Objects Close to an Antenna Antenna Factor Near-Field H Antennas and Probes Shielded H-Field Probe Magnetic-Core Rod Antenna Near-Field E Antennas and Probes Loop vs. Rod Antenna Friis's Formula Fields from a Distant Source Appendix A: Summary of the Three Major Coordinate Systems A-l Appendix B: Definitions for Common and Uncommon Functions B-l Appendix C: Conversion, Unit, and Notation Tables C-l Appendix D: Helpful Mathematical Relationships D-l References R-l Index 1-1 xxix