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NOISE REDUC TION TELHNINUES IN ELECTRONIC SYSTEMS Second Edition Dá Henry W.Dtt NOISE REDUCTION TECHNIQUES IN ELECTRONIC SYSTEMS SECOND EDITION Henry W. Ott Distinguished Member of Technical Staff AT&T Bell Laboratories WILEY A WILEY-INTERSCIENCE PUBLICATION JOHN WILEY & SONS New York * Chichester º Brisbane º Toronto * Singapore PREFACE Much has occurred to affect the field of electromagnetic comparibility (EMC) in the 11 years since the first edition of this book was published, The two most important developments are the proliferation of digital electronics in the consumer marketplace and the establisament of rules on emission control from digital systems by the Federal Communications Commission (FCC). As a result interest in the subject of EMC has increased dramati- cally The first edition covered basic theory anil emphasized reducins the susceptibility of electronic systems. There is now a need for information on controlling the emission from electronic systems, especially digital 5 and on low-cost techniques for providing EMC for consumer products sold in a competitive market. In addition there is increased concern about the susceptibility of electronic systems to electrostatic discharge. This edition was written LO address these issues. Virtually all the material contained in the first edition is still applicable aad has been retainud. Three new chapters have been added on the subjects of noise und radiation from digital electronics and electrostatic discharge. Chapter 1 was rewritten und now includes material on the FCC regu- Tations. Chapters 2 to 7 were updated and contain new material, Chapters 8 and 9 are unchanged; Chapters 10, 11, and 12 are new. Chapter 10 covers digital circuit noise and layout, Chapter 11 is on digital circuit radiation, and Chapter 12 deals with electrostatic discharge. In addition a new appendix has been included on FCC EMC test procedures (Appendix F) 1 would like to express my gratitude and appreciation to all those who took the time to comment on the first edition of the book, and to those who encouraged me to write this second edition. In particular, 1 would like to thank Scott Roleson, Bob German, and Dr. Clayton Paul for the many fruitful discussions we had on the subjcet of EMC. Lowe a special debt of appreciation to Eva Carter for her superb editing of the manuscript. À special thank: bes to Dan Johnson who worked out all the problems in the first edition and pointed out errors. Finally, 1 would like to thank all my colleagues who took the time to review this manuscript and make useful comments and suggestions. Henry W. Orr Livingston, New Jersey dly 1987 vil PREFACE TO FIRST EDITION This book covers the practical aspects of noise suppression and control in electronic circuits. It is intended primarily for the practicing engineer who is involved in the design of electronic equipment or systems, and also as a text for teaching the practical aspects of noise suppression. The concepts of noise reduction presented in the book can be applied to circuits operating from audio frequencies through VHF. More emphasis is placed on low- to mid-frequency noise problems, however, since these are the least documen- ted in existing literature, Some of the most difficult and frustrating problems faced by design engineers concern elimination of noise from their circuits or systems. Most engineers aré not well equipped to handle noise problems, since the subject is not normally taught in engineering schools, and what literature is avail- able is widely scattered among many different journals. Solutions to noise problems are usually found by trial and error with little or no understanding of the mechanisms involved. Such efforts are very time consuming and the solutions may prove unsatisfactory if the equipment is moved to à new environment. This situation is unfortunate, since most of the principles involved are simple and can be explained by elementary physic: This text began as a set of lecture notes for an out-of-hours cour: at Bell Laboratories and later presented as part of the in-hours continuing education program at the laboratories. The approach used in the text is design oriented, with the amount and complexity of mathematics kept to à minimum. In some cases, models representing physical phenomena have been simplified to provide more useful results, By making realistic simplify- ing assumptions, results having clear physical meaning are obtained. The organization of the material is às follows, Chapter 1 is an intro- duetion to the subject of noise reduction. Chapters 2 and 3 cover the two primary means of noise control: shielding and grounding, respectively. Chapter 4 covers other noise reduction techniques such as bulancing, decoupling. and filtering. Chapter 5, on passive components, covers the characteristics that affect Lhe components” noise performance and their use in noise reduction circuitry. Chapter 6 provides a detailed analysis of the shielding elfectiveness of metallic sheets. Chapter 7 covers relays and switches and discusses methods of reducing noise generated by these de Chapter 8 covers intrinsic noise sources that result in a theoretical Iw xd 3 GROUNDING Safety Grounds, 73 Signal Grounds, 75 Single-Point Ground Systems, 77 Multipoint Ground Systems, 79 Hybrid Grounds, 81 Functional Ground Layout, 82 Practical Low-Frequency Grounding, 82 Hardware Grounds, 84 Single-Ground Reference for a Circuit, 86 Amplitier Shields, 88 Grounding of Cable Shields, 89 Ground Loops, 93 Low-Frequency Analysis of Commmon-Mode Choke, High-Frequency Analysis of Common-Mode Choke, Differential Amplifiers, 102 Shield Grounding at High Frequencies, 105 Guard Shields, 106 Guarded Meters, 110 Summary, 113 Bibliography, 114 4 BALANCING AND FILTERING Balancing, 116 Power-Supply Decoupling, 122 Decoupling Filters, 126 Amplifier Decoupling, 128 Driving Capacitive Loads, 130 High-Frequency Filtering, 133 System Bandwidth, 134 Modulation and Coding, 134 Summary, 137 Bibliography, 137 5 PASSIVE COMPONENTS Capacitors, 137 Inductors, 143 Transformers, 145 Resistors. 146 s6 100 CONTENTS 73 16 137 CONTENTS Noise in Resistors, 147 Conductors, 149 Ferrito Beads, 152 Summary, 157 Bibliography, 158 SHIELDING Near Fields and Far Fields, 159 Characteristic and Wave Impedances, 162 Shieiding Effectiveness, 164 Absorption Loss, 166 Reflection Loss, 169 Composite Absorption and Reflection Loss, 178 Summary of Shielding Equations, 180 Shielding with Magnetic Material, 182 Experimental Data, 185 Apertures, 187 Waveguide Below Cutoll, 192 Conductive Gaskets, 198 Conductive Windows, 185 Conductive Coatings, 196 Cavity Resonance, 198 Grounding of Shields, 199 Summary. 199 Bibliography, 202 CONTACT PROTECTION Glow Discharges, 203 Metal-Vapor or Are Discharges. 204 AC versus DC Circuits, 206 Contact Material, 207 Contact Rating, 207 Loads with High Inrush Currents, 208 Inductive Loads, 209 Contact Protection Fundamentals, 211 Transient Suppression for Inductive Loads, 216 Contact Protection Networks for Inductive Loads, 219 Inductive Loads Controlled by a Transistor Switch, 222 Resistive Load Contact Protection, 223 dit 159 203 xiv 10 Contact Protection Selection Guide, 224 Examples, 224 Summary, 226 Bibliography, 226 INTRINSIC NOISE SOURCES Thermal Noise, 228 Characteristics of Thermal Noise, 232 Equivalent Noise Bandwidth, 234 Shot Noise, 238 Contact Noise, 238 Popcorn Noise, 239 Addition of Noise Voltages, 240 Measuring Random Noise, 241 Summary, 242 Bibliography, 243 ACTIVE DEVICE NOISE Noise Factor, 244 Measurement of Noise Factor, 246 Caleulating S/N Ratio and Input Noise Voltage from Noise Factor, 249 Noise Voltage and Current Model, 250 Measurement of V and |, 253 Calculating Noise Factor and S/N Ratio from Vl, 258 Optimum Source Resistance, 255 Noise Factor of Cascaded Stages, 257 Noise Temperature, 260 Bipolar Transistor Noise, 261 Junction Field Effect Transistor Noise, 264 Noise in IC Operational Amplifiers, 257 Summary, 272 Bibliography, 272 DIGITAL CIRCUIT NOISE AND LAYOUT Frequency versus Time Domain, 275 Analog versus Digital Circuits, 276 Digital Logic Noise, 278 CONTENTS 228 244 274 CONTENTS 11 12 Internal Noise Sources, 277 Digital Circuit Ground Noise, 280 Power Distribution, 286 Noise Voltage Objectives, 293 Measuring Noise Voltages, 294 Unused Inputs, 295 Logic Families. 295 Summary, 296 Bibliography, 206 DIGITAL CIRCUIT RADIATION Differential-Mode Radiation, 208 Controlling Difterential-Mode Radiation, 308 Common-Mode Radiation, 313 Controlling Common-Mode Radiation, 315 Engineering Documentation and EMC, 319 Summary, 319 Bibliography, 320 ELECTROSTATIC DISCHARGE Static Generation, 322 Human Body Model, 327 Static Discharge, 330 ESD Protection ih Equipment Design, 332 Software and ESD Protection, 344 ESD versus EMC, 348 Summary, 348 Bibliography, 349 APPENDIX À The Decibel Using the Decibel for Other Than Power Ratios, Power Loss or Negative Power Gain, 353 Absolute Power Level, 353 Noise Measurements, 354 Crosstalk Units, 356 Summing Powers Expressed in Decibels, 256 APPENDIX E Summary of Noise Reduction Techniques Xv 298 322 351 359 a ms + EYMBOLS Direct current 1/f-noise current Ground current Gute leakage current Load current Arbitrary noise current Differential mode current Common-mode current Current in nth harmonic Equivalent input noise current Current at time 1=0 Source current Shield current Shot noise current Thermal noise current Instantancous current Unit vector along imaginary axis Arbitrary integer Constant Boltzmann's constant Coefficient of magnetic coupling Inductante Series inductance of capacitor Shield inductance Distributed inductance of transmission line Length Mutual inductance Integer Network function Integer Noise figure Power Noise power outpuL Charge Quality factor Charge on electron Resistance Reflection loss (dB) ac resistance SYMBOLS Re. R. Ras Re Ro = ERR Rad Ri E dE = SS gs & xix Conductor resistance Series resistance of capacitor de resistance Resistance of fuse Ground resistance Load resistance Shield resistance Source resistance Source resistance for minimum noise factor Distributed resistance of transmission line Radius Base resistance in Y-equivalent transistor model Collector resistance in Fequivalent transistor model Emirter resistance in T-equivalent transistor model Shielding effectiveness (dB) Signal-to-noise power ratio Signal-to-nvise improvement factor Period Temperature Equivalent input noise temperature Standard reference temperature Time Thickness Pulse rise time Valtage Minimum arcing voltage Glow discharge breakdown voltage Commoen-made noise voltage Contact voltage Supply voltage de voltage Ground voltage Glow discharge sustaining voltage Load voltage Differential (metallic) noise voltage Arbitrary noise voltage Equivalent input noise voltage Equivalent input device noise voltage Output noise voltage x x ss aim NNNNNNSNAN E md TER mM Fes 1 E Total equivalent input noise voltage Source voltage Shield voltage Thermal noise voltage Width of conductor Impedance Collector impedance Emitter impedanee Load impedance Characterístic impedance of transmission line Characteristic impedance of medium Shield impedance Transfer impedance Wave impedance Common base current gain Common emitter current gain Correlatioa coclficient Skin depth Diglectric constant Relative dielectric constant Damping factor Shicld factor Angle Wavelengih Permeability Relative permeahility 3.1416 Resistivity Relative re: Conductivity vily Relative conduetivity Decay time Magnetic flux Radian frequency (27) Za, avYMBOLS NOISE REDUCTION TECHNIQUES IN ELECTRONIC SYSTEMS SECOND EDITION LIND olave a aJNBOM DNINLHOM 1Sv20voHa No Jum page “dsapadas Pr =] y | y Í k | Ú | ' Pr ANA aims, EE EE Te e ! : ! Hi | —— | Add 7 E RE à ! amb Ala as Haxvaas e E Haiaigaiav. Halanidioy Le e] Po datam pd Holoa120 a Haxin fel ne + : 4 Na di f ” | | i 1 esssd e | pr a Holviioso ONITANOS JINVOIHI NOWNOS ' SNITdNIOO JALIDNONOS m-—— ——— ONNANIDO Grata DILINDUIM CT > ONTANDO ais DiHISa13 q SN —— VNNILNT 1 INTRODUCTION TELEPMONE LINES Ch 200 HD] TELEVISIOA eiprment such as this ratio cam êmut noise that may interfer arher naideranom of noise during equipment design cum uvena these e Noise is any clectrical signal present in a circuit other than the desired Signal. This definition does not apply to the distortion products produced in a circuit due to nonlinearities. Although these distortion products may be undesirable, they are not considered noise unless they get coupléd into another part of the circuit. It follows that a desired signal in one part of a ircuit is considered to be noise only if coupled to some other part of the circuit. Noise sources can be grouped into three categories: (1) intrinsic noise sources lhat arise from random fuctuations within physical systems. such as thermal and shot noise, (2) man-made noise sources, such motors, switches, digital electronies, and radio transmitters. and (3) noise due to natural disturhances, such as lightning and sunspots. Interference is the undes . able effect of noise. If a noise voltage causes improper operation of a ciremit, it is interlerençe. Noise cannot be elimi nated but only reduced in magnitude, until it no longer causes interference, DESIGNING FOR ELECTROMAGNETIC COMPATIBILITY Electromagnetic compatibility (EMC) is the ability of an electronic system to (1) function properly in its intended electromagnetic environment. and DESIGNING FOR ELECTAOMAGNETIC COMPATABILITY 5 (2) not be 4 source of pollution to That environment. The electromagnetic environment is composed of both radiated and conducted energy. EMC therefore has two aspects, emission and susceptibility. Susceptibility is the capability of a device or circuit to respond to unwanted electrical energy (i.e., noise). The susceptibility level of a circuit or device is the nóise environment in which the equipment can operate satisfactorily, without degradation, and with a defined margin of safety. The opposite of susceptibility is immunity. One difficulty in determining immuni- ty (or susceptibility) levels is defining what constitutes performance degra- dation. Emission pertains to the interference-causing potential of a product. The purpose of controlling emissions is to limit the clectromagnetic energy emitted, and thereby control the electromagnetic environment in which other products must operate. Controlling the emission from one product may eliminate an interference problem for many other products. Therefore it is desirable to control emission in an attempt to produce an elec- tromagnetically compatible environment. To some extent susceptibility is self-regulating. If a producer is susceptible to the environment, the customer will become aware of it and may not continue to purchase it. Emission, on the other hand, tends not to be selt-regulating. A procduet that is the source of emission may not be affected by that emission. As a result various regulatory bodies have imposed standards to control emissions from certain classes of producis. EMC design can be approached in either of two ways: one is the erisis approach, and the other is the systems approach. In the c approach the designer proceeds with u total disregard of EMC until the design is finished, and testing or—worse yet—field experience suggests that a problem exists. Solutions, implemented at this late stage. are usually expensive and consist of undesirable “add-ons.” This is often referred to as the “Band-Aid” approach. As equipment development progresses from design to testing and to production, the variety of noise mitigation techniques available to the designer decreases steadily, Concurrently. cost goes up. These trends are shown in Fig. 1-4. Early solutions to interterence problems, therefore, are usually best and least expensive. The systems approach considers EMC throughout the design; the de- signer anticipates EMC problems at the beginning of the process, finds the remaining problems in the breadboard and early prototype stages, und tests the final prototypes for EMC as thoroughly as possible. This way EMC becomes an integral part of both the electrical and mechanical design of the product. As a result EMC is designed intoand not added onto—the product, and this is a more cost-elfective approach. Tf noise suppresston is considered for one stage or subsystem at a time when the equipment is being designed, the noise mitigation techniques are simple and straighilorward. Experience has shown that when noise suppres- sion is handled this way. the designer should be able to produce equipment 1 = INTRODUCTION These regulations were the result of increasing complaints to the FCC about interferencc to radio and television reception where digital clectronics were identified us Lhe source of the interferenec. In this ruling the FCC said Computers have been reported to cause interference to ulmost all radio services, particularly those services below 200 MHz, including police, acronautical, and broadcast services. Several factors contributing to this include: (1) digital equipment has become more proliÃe throughout our society and are now being sold for use in the home; (2) technology has increased the specds of computers to the point where the computer destgner is now working with radin frequency and electromagnetic interference (EMI) problems— something he didn't have LO contend with 15 years ago; (3) modera production economies has replaced the stecl cabinets which shield or reduce radiated emanation with plastic cabinets which provide litile or no shieldine. The FCC defines « computing device as Any electronic device or system that gencrates and uses timing pulses at a rate in excess of 10,000 pulses (cycles) per second and uses digital techniques: inclusive of telephone equipment ihat uses digital techniques or uny device or system that generates and utilizes radio frequency energy for the purpose of perlorming data processing functions. such as electronic computations, oper- ations. transformations, recording, filing, sorting, store retrieval or transfer... “This definition was intentionally made broad to include as many products as possible. Thus, if a product uses digital circuitry and has a clock frequency greater than 10 kHz, it is à computing device under the FCC definition. This definition covers most digital electronies manufactured today. Computing devices covered by this definition are divided into two classes: Class A: À computing device that is marketed for use in à commercial, industrial, or business environment. Class B: À computing device that is marketed for use in a residential environment, notwithstanding its use in a commere ul, indus- trial, or business environment. Since Class B devices are more likely to be located in closer proximity to radio and television receivers, the emission limits for these devices are about 10 dB more restrictivc than those for Class À devices. Mecting these technical standards is the obligation of the manufacturer or importer of a product. To guarantee compliance, the FCC requires the manufacturer to test the product for compliance before the product can be marketed in the United States. The FCC defines marketing as shipping, selling, offering for sale, importing, and so on. Therefore, until a product EMC REGULATIONS a complies with the rules, it cannot legally be advertised since this enuld be considered an offer for sale. In order to legally advertise a product prior to compliance, the advertisement must contain a statement that the device is subject to FCC rules and will comply with the rules prior to delivery. For personal computers and their peripherals (a subeategory of Ch es BJ. the manufacturer must submit the test data to the FCC and obtain certi- ficarion from the ECC before it can market the product. The Commission can, if it so desires, ask for a sample product to test before providing the certification. For all other products (Class A and Class B— other than personal computers and their peripherals) the munufacturer must verify compliance by testing the product before marketing it. Verification isa seli-certification procedure where nothing is submitted to the FCC unless specifi ly re- quested. Compliance is by random sampling of products by the FCC - The time required to do the compliance tests (and re-do them if the product fails), and the time required to obtain certification from the Commission (if required), should he scheduled into the produet's develop- ment timetable. o Testing must be done on a sample thar is representative of production units. This usually involves à production or preproduction model, Com- pliance testing must therefore he one of the last items in the development timetable. This is no time for unexpected surprises! If the product fails the test, changes at this point are difficult und expensive. Therefore it is desirabl: to approach the final compliance test with a high degree or confidence that the product ill pass. This cam be done iE (1) proper EMC design principles (as discussed in this book) have been used throughout the design and (2) preliminary emission testing was done on carly madels and subassemblies. These rules not only specify the technical standards (limits) that a product must satisfy but also the administrativc procedures that must he followed and the measuring methods that must be uscd to determine compliance. It should be noted that the limits and the measurement procedures are interrclated. The derived limits were based on specified measurement procedures. Therefore compliance measurements must be made following the procedure outlined by the ECC in FEC/OST MP-4 “ECC Methods of Measurement of Radio Noise Emissions from Computing Devices” (ser Appendix F). Tests must be made on à complete system. with all cables connected and configured in a reasonable way that tends to maximize the emission. For radiated emission the measurement procedure specifies an open ficld (or equivalent) measurement made over a ground plune with a tuncd dipole (or other correlatable, lincarly polarized) antenna- This is shown im Fig. 1-5 Table 1-1 gives the radinted emission limits for a ss À product when measured at a distance of 30m, and Table 1-2 lists the limits for a Class B product when measured at a distance of 3m. ANTENNA SEARCH HEIGHT 4-4 m (2-6 mj + HORIZONTAL E VERTICAL FOLARIZaTiON. 80-00 cm” E GROUND PLANE EMI RECEIVER Figure 1.5, Opun fisld' tesr site for FCC radimieil emission tese. Equiipament under test (EL om the turntabie. Table 1-1 FCC Class A Radiated Emission Limits Measuring, Field Frequency Distance Strength (MHz) fm) (uMim) 30-88 30 3 BE-216 30 5 216-1000 30 m Table 1-2 FCC Class B Radiated Emission Limits Meusuring Field Frequency s Strength (MHz) (m) fuVim) 3u-s8 3 tm 88-216 3 15u 216-1000 3 200 10 EMC REGULATIONS AM A comparison between lhe Class A and Class B limits must be done at the sume measuring distance. Therefore, if the Class A limits are extrapolated to the 3-m measuring distance (using a 1/r extrapolation), the two sets of Fmits can then be compared as shown in Pig. 1-6. As can be seen, the Class B limits are more restrictive by about a factor of 3 (10 dB). Conducted emission limits are specified in the rules because the FCC believes that at Ireguencies below 30 MHz the primary cause of interference with communications occurs by conducting rf energy onto the ac power line and subsequently radiating it from Lhe power line, Table 1-3 shows both the Class A and B conducted emission limits. These voltages are measured common-mode (hot to ground, and neutral to ground) on the ac power line using à 50/50 dl line impedance stabi zation network (LISN) as specified in the measurement procedure (see Appendix F). Figure 1-7 shows a typical FCC-conducted emission test setup. Not only must a device be tested for compliance with the technical standards, but it must also be labeled as compliant, and information must be provided to the user on its interference potential. To adeition to the technical specifications mentioned earlier. the rules also contain a noninterference requirement which states that if use of the product causes harmtul interference, the user can be required to cease operation of the device. Notice the difference in responsibility between the technical if MEASURING DISTANCE =3m CLASS A 500 + 400 ê = 1 FIELD STRENGTH (uVim) 300 200 EL 10 EU so 100 200 300 sa «00 FREQUENCY [MHz] Figure 1-6. ECC Part 15, Subpurt J rediored emission fímits measured at a distance of 3 m Eis ? INTRODUCTION French). CISPR was formed in 1934 to determine measurement methods and limits for radio-frequeney interference in order to facilitato international trade. CISPR has no regulatory authority, but its standards, when adopted by governments, become national standards. In 1985 CISPR adopted a new set of emission standards (Publication 22) for Information Technology Equipment (digital electronics). Many European countries have adopted these requirements as their national standard, and more are expected to do so in the future. The United States, as à voting member of CISPR, voted in favor of the new standard. This put considerable pressure on the FCC to adopt the same standarcis, Therefore the limits of CISPR Publication 22 are likely to become the international EMC standard. Figure 1-8 compares the new CISPR radiated emission standard with the present FCC standard. The FCC limits have been extrapolated to a 10-m measuring distance for this comparison. As can be seen, the CISPR limits are more restrictive in the frequency range from 88 to 230 MHz. From &8 to 216 MHz the CISPR Class A limit is 3,5 dB more restrictive, and from 216 to 23) MHz the CISPR Class A limit is 6.5 dB more restrictive than the present FCC requirements. Figure 1-9 compares the new CISPR narrowband conducted emission standard to the present FCC standard. A major diffrence is that CISPR imposes « limit in the freguency range of 150 to 450) kHz where no ECC limit presently exists. For Class A products the CISPR standard is 9.5dB more restrictive from 1,6 MHz to 30 MHz. For Class B produets the CISPR standard is 2dB more restrictive from 0,5 to 5 MHz, 50 j | MEASURING DISTANCE =10m ss | cai = ps] E EE [| E CLASS À E Gisa el E O E Ea z E af [a e E | CLass E a 81 I CISPA ] q = =====— m IE u E 3 E fe Lit I Lista) 10 20 3 Eu 100 200 300 500 “1000 FREQUENCY (MHz) Figure 1-8. FCC Part 15, Subpar ond CISPR. Publication 22. rediated emission limits mensuree ar a distance of 10 m EMC REGULATIONS 15 7a | — l 85 I CLASS A — E I a CISPR = E | ca - uu E EH ss - - fo) s Cispa 50 emo grain SS Do CLass a FCC 45 E) L a a L14 LIL l LAJ4I da 02 03 05 1 28 5 w ao 30 So 170 FREQUENCY [MHz] Figure 1-9. FCC Par 15, Subpori J und CESPR, Publicarion 22. nurrowband conducted emisgion limits. Susceptibility In August 1982 the U.S. Congress amended the Communications Act of 1934 (House Bill 43239) to give the FCC authority to regulate the suscep- tibility of home electronics equipment and systems. Examples of home electronic equipment are radio and television sets, home burglar alarm and security systems, automatic garage door openers, electronic organs, record turntables, and stereo/high fidelity amplifier systems. Although this legista ton is aimed primarily at home equipment and systems, it is not intended to prevent the FCC from adopting standards for devices that are also used ouiside the home. To date, however, the FCC has not aeted on this authority. Although it published an inquiry into the Problem of Radio Frequency Interference to Electronic Equipment (General Docket No 78-369), the FCC relies on self-regulation by industry. Should industry become lax in this respect, the FCC may move to exercise its jurisdiction Surveys of the electromagnetic environment (Heirman 1976; Janes 1977) have shown that a field strength greater than 2 Vim oveurs about 1% of the time. Since there is no | susceptibility requirement for commercial equipment, a reasonable immunity level objective would be 2 Vim. The government of Canada has released an Electromagnetic Compatibili- ty Advisory Bulletin (EMCAB 1) in which it defines three levels or grades of immunity for electronic eguipment and states the following; 16 1: INTRODUCTION | 1. Products that meet GRADE 1 (1 Vim) ate likely to experience performance degradation. - Products that meet GRADE 2 (3 Vim) are unlikely to experietce degradation. « Products that meet GRADE 3 (10 Vim) should experience pertorm- ance degradation only under very arduous circumstances. e) pa MAGNETIC FIELD E ELECTRIC ANO ELECTROMAGNETIC Military Standards Another important group of EMC specifications are those issucd by the > E U.S. Department of Defense. MIL-STD-461B speçifes the limits that must Dj IE Ê be met, and MIL-STD-462 specifies the test methods and procedures for Es Es já pai É making the tests contained in MIL-STD-461B. These standards are more tu o ti uy séz E stringent than the FCC regulations because they cover suscept y as well E a Z| EE gê = z as emission, and the frequency range from 30 Hz to 40 GHz. “E je E i us E É The test procedures specified in MIL-STD-462 are quite different than 3 E - E those specified by the FCC, and this makes direct comparison of the z = requirements difficult, For radiated emission the military standard species ER 8 enclosed chamber (shielded room) testing, whereas the FCC rules tequire aro fem open ficld testing. For conducted emission testing the military measures eu P] E current and the FCC measures voltage. Ecu Ea o5 The categories of tests specified by MIL-STD-461B are organized as SE9 E E shown in the block diagram in Fig. 1-10. Tests are required for both radiated = Ei e e E and conducted emissions as well as radiated and conducted suseptibility. a | u sê Table 1-4 is à list of the emission and susceptibility requirements established a & ir by MIL-STD-461B. The Military Specification is a comprehensive docu- E z am ment, and can also be used by industry as a guideline for designins E di] interference-free nonmilitary equipment, im extes tests of conducied and radiuted - ed z a TYPICAL NOISE PATH SE E : ain E] au = E sê E ã& El: A block diagram of a typical noise path is shown in Fig. 1-11. As can be ua E as E E seen, three elements are necessary to produce a noise problem. First, there E Ea E É must be a noise source. Second, there must be a receptor circuit that is = Z5õ É suseptible to the noise. Third; there must be à cotpling channel to transmit E Sa z the noise from the source to the receiver. The frst step in analyzing a noise problem is to define the problem. This is done by determining what the noise source is, what the receptor is, and how the source and receptor are coupled together, It follows that there are Lhree ways to break the noise path: (1) the noise can be suppressed at the source, (2) the receptor can he made insensitive to the noise. or (3) the transmission through the coupling channel can be minimized. In some cases, noise suppression techniques must be applied to two or to all thres parts ol the noise path. CONDUCTED