Automotive EMC Design And Applications

EMC Overview What is EMC? Why is it Important? Case Studies. Examples of calculations used in EMC.EMC Overview1

What Is “EMC”? Electromagnetic Compatibility (EMC): Theprocess of determining the interaction betweenelectrical and electronic devices with respect tounwanted effects due to:– Electromagnetic Interference (EMI)– Radio Frequency Interference (RFI)EMC Overview2

EMI / RFI and theElectromagnetic SpectrumEMC Overview3

Challenge of EMC Typical EMC problems can involveany combination of the disciplines andmay vary as a function of the frequencyof the electromagnetic energy involved.EMC Overview4

Physics of Electromagnetic(E/M) Waves Documented in “Maxwell’s Equations” whichstate:– A changing magnetic (H) field creates a changingelectric field.– A changing electric (E) field creates a changingmagnetic field.– An enclosed charge creates an electric field.– There can not be magnetic “monopoles”. Detailed by Professor Maxwell in his 1864 paper:“A Dynamical Theory of the Electromagnetic Field”EMC Overview5

As Professor Maxwell stated EMC Overview6

Prof. Maxwell continued EMC Overview7

and then said EMC Overview8

Metrics of Electromagnetic(E/M) Waves Travel at/near speed of light (in vacuum/air/freespace) (nearly) 3.00 x 10 8 meters/sec. Can be expressed as frequency. “Length” of one cycle is expressed as“wavelength”, or “Lambda”.– Lambda ( l ) Propagation speed / frequency– For 1 MHz, l 300 meters– As frequency increases, wavelength decreases. Frequency and wavelength used interchangeably.– E.g. 15 MHz 20 meterEMC Overview9

Terminology in EMC – RFSignals Radio Frequency (RF) – E/M wavefrequencies used typically forcommunication. kHz – 1 x 10 3 Hertz (cycles per second) MHz – 1 x 10 6 Hertz GHz – “1000 MHz”, or 1 x 10 6 Hertz THz – 1 x 10 12 HertzEMC Overview10

Circuit Theory “Quiz” Every current must return to it’s source. The path of the “source” and “return”current should be determined. Current “takes the path of least”.EMC Overview11

Circuit Theory Realities! Path is by “conduction” or “displacement”. The majority of the current takes the path ofleast impedance.– If current is DC (impedance is determined byresistance).– If current is not DC (including pulsed DC),impedance is determined by reactance. Capacitance determined by conductor proximity Inductance determined by current loop pathEMC Overview12

What Do These SymbolsMean?EMC Overview13

What is “Grounding”?From “PCB Design for Real-World EMI Control”, by Dr.B.ArchambeaultEMC Overview14

Early “Ground” ConnectionsEMC Overview15

Risk of Using “Ground” AsReturn Path “Assumption” is that “ground” has zero (0)impedance for all frequencies. Since impedance cannot be zero (0) for allfrequencies – at some point the current will NOTflow along the" ground” path, when other paths oflower impedance exist!EMC Overview16

Is This “Grounding”?EMC Overview17

Better Use of Return andGround SymbolsEMC Overview18

Important “Take-Away”Points Signal ground not equal to signal return. Misconceptions:– A “good ground” reduces noise. What is a good ground? When does it occur?– The path the engineer believes is ground is theactual power (or signal) return path.EMC Overview19

The EMC “Model”SourcePathPathReceiver The EMC model consists of three key elements– In theory, elimination of any element will eliminateEMC issues.– In practice, we can only minimize their impact.EMC Overview20

Use of the EMC Model Items to consider – nature of the “source”(such as high “E-field”, “H-field”, or planewave conditions). “Path” of the current flow (either conductedor by displacement). Receiver of the energy – “intentional” or“unintentional”.EMC Overview21

The “Source-Path-Receiver”Interaction The path of the energy to the receiver may be viaradiation or conduction. If path is radiated, the intensity is reduced as afunction of distance (similar to a flashlight )- theintensity is lower the greater the distance away the “inverse distance” property.EMC Overview22

The Radiated Path The E-field and Hfield vectors areorthogonal to eachother (always at 9:00position). Direction ofpropagation isorthogonal to vectors.EMC Overview23

Radiated “Regions” The radiated E/M wave characteristics depend onthe distance of source from the receiver. Primary regions are “Near Field” and “Far Field”.EMC Overview24

Near and Far Field Physics Location of a receiver in the near field mayaffect the source and a receiver in the farfield has no impact upon the source. The E/M wave in each region has a“Characteristic Impedance” of Zw. In the far field, the Zw 377 ohms.EMC Overview25

Near Field Physics In the near field Zw 377 or 377 ohms. Wave impedance is determined by:Zw E / H E is the electric field vector.H is the magnetic field vector. For a low Z source, H-field dominates. For a high Z source, E-field dominates.EMC Overview26

The Conducted Path Conducted paths have only small reductionsin magnitude from source to receivers. Are due to currents that travel on circuitwiring and/or conductive assemblies.EMC Overview27

Why Wiring Effects AreImportant in EMC Work Early electrical and electronic systems had fewcomponents to be connected - recent systemshave increased wiring complexity. Many engineers don’t focus on “just pieces ofwire” and they may just attach these wires to“GROUND”! Wiring will still be used for many systems in thefuture, therefore it’s critical to understandrelevant physical parameters.EMC Overview28

Electrostatic Discharge (ESD) Exhibits conditions similar to both radiated andconducted paths. High voltage ( 4 - 25 kV) discharges. Can cause immediate failure or induce latentdefect (such as in manufacturing process ofcustomer use).EMC Overview29

Electrical and ElectronicSystems as Sources of RF Noise Most electrical and electronic systems can beresponsible for RF noise generation as a byproductof their normal operation. In many industries, this noise has been classifiedinto two categories:– Broadband (typically due to electrical arcing)» Referred to as “Arc and Spark” noise.– Narrowband (typically due to active electronics)» All other noise NOT due to “Arc andSpark”.EMC Overview30

Types of (“Noise”) Sources eAmplitudeFrequencyFrequencyNarrowband NoiseBroadband Noise Broadband noise is greater than the “width” ofreceiver of the energy. Narrowband noise is less than the “width” of thereceiver.EMC Overview31

“Broadband” Characteristics Spectrum (frequencies and amplitude)changes with time. Sources include high voltage dischargecomponents and similar pulse-typesystems. Brush-type motors also are sources.EMC Overview32

Causes and Effects ofBroadband Noise Typical sources include high-voltage devices andinductive elements. Can be difficult to control. Most noticeable effects may be on “intentional”receivers:– AM reception may have audible noise.– FM reception may lose some sensitivity. Can also cause “unintentional receivers” to react.EMC Overview33

Consequences Of BroadbandNoise Sources BAD –Due to functions that are required forsystem functionality (such as motors or inductivedevices). BAD – Can have both conducted AND radiatedcoupling paths. GOOD – Energy spread out – may have minimaleffect on potential receivers (intentional andunintentional).EMC Overview34

“Narrowband” Characteristics Usually contains discrete frequencies. Typical sources are activesemiconductor components - includingmicroprocessors.EMC Overview35

Spectral Representation ofNarrowband Noise Result is a spectrum of a “comb-like” appearance. Spectrum stays approximately constant over time.EMC Overview36

Characteristics OfNarrowband Noise Sources May only affect specific frequencies. Receivers can appear to function “almostnormal”. Can be addressed in component designprocess.EMC Overview37

Common Sources ofNarrowband Noise Digital logic MicroprocessorsEMC Overview38

Microprocessors AndNarrowband Noise Common source ofNarrowband noise. Logic states depend onclocking from asquare-wave source. Square waves containmany frequencies which extend far intothe radio spectrum.EMC Overview39

Why Clock Signals CreateNoiseSpectrum of Clock o5fo6fo7fo8foFrequency (xFo) Fourier series expansion explains emission profile. Shows many frequencies in square wave. Goal is to filter out higher frequencies.EMC Overview40

Consequences Of NarrowbandNoise Sources BAD -May be many sources in a system due toproliferation of active devices. BAD - Receivers (both intentional andunemotional) can appear to function “almostnormal”. GOOD - Can be addressed in component designprocess OR can be identified by testing.EMC Overview41

Unintentional Reception ofEnergy The reception of energy by either unintentionalreceivers or reception of energy that the receivershave NOT been designed to receive is also aconcern. This is known as “Susceptibility” or “Immunity”.– Susceptibility- “Glass half empty.”– Immunity – “Glass half full.”EMC Overview42

Immunity Issues Can ExistDue To The Following Most of today’s electrical and electronic systems relyon active devices such as microprocessors and digitallogic for:– Control of system functions.– User convenience / features.– Legislated system requirements (such as mobile telephonelocation reporting). With today’s vast networks for data communicationthere are serious implications when disrupted.EMC Overview43

EMC Case Studies Emissions: Microprocessor clockharmonic was on a two way radiofrequency – rendering radiocommunication impossible. Immunity: Production plant alarms wereset when hand held radios were used nearthe control panel!EMC Overview44

Why is EMC Important to AllIndustries and Business? Today’s electronic systems contain many moreactive electronic components than in the past. Those components and assemblies may emit RFnoise or be exposed to external sources ofinterference - resulting in changes systemoperation, perhaps even having safetyimplications.EMC Overview45

EMC Overview 43 Immunity Issues Can Exist Due To The Following Most of today’s electrical and electronic systems rely on active devices such as microprocessors and digital logic for: –Control of system functions. –User convenience / features. –Legislated system requirements (such as mobile telephone location reporting). With today’s vast networks for data communication there .