PCB电磁干扰算法.pdf

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1、Radiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge Effectsin Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)in Printed Circuit Boa

2、rds(PCBs)in Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)Dr.Zorica Pantic-TannerDirector,School of EngineeringDirector,Center for Applied Electromagnetics San Francisco State Universityzptsfsu.

3、eduFranz GisinManager,Electromagnetic CompatibilityNortel NSCHOOL OF ENGI NEERI NG Motivation Problem definition Problem setup Physics of PCB propagation modes Physics of PCB edge effects Minimizing radiation from PCB edgesRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge Eff

4、ectsRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge Effectsin Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)in Pri

5、nted Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)MotivationMotivationMotivationMotivationMotivationMotivationMotivationMotivationAs competitive forces drive product costs down,it becomesincreasingly important to incorporate good EMC designpractices into the prod

6、uct-especially ones that providesuperior suppression at minimum cost.Because PCB layout patterns(how traces and ground/powerplanes are stacked and routed)do not add to production costs,there is a tremendous interest in optimizing these structures toprovide maximum EMC suppression.The material presen

7、ted tonight highlights some of the ongoingresearch in this area that the SFSU Center for AppliedElectromagnetics is currently working on in conjunction withits Industry Partnership Program.MotivationMotivationMotivationMotivationMotivationMotivationMotivationMotivationIEEE EMC Society Computational

8、Electromagnetics TC-9 identified edgeemissions as a significant EMC risk phenomenon,and included it as one ofits four challenging EMC modeling problems.Find the edge emissions from the following structure.MotivationMotivationMotivationMotivationMotivationMotivationMotivationMotivationSolution(from a

9、 modeling perspective)Find a big fast computer with enough memory to hold the entire model.Take a long coffee break.Results to be presented at the IEEE 2000 EMC SymposiumSolution(from a modeling perspectiveFind a big fast computer with enough memory to hold the entire model.Take a long coffee break.

10、Modeling entire structure on a computer does not provideinsight into whats going on.If we“unbundle”the problem into its component pieces,lookat the physics of each component,we can use the insightgained from this process to figure out what is going on.How bad is it?Does the 20H rule(pulling back pow

11、er planes)work?Does fencing(grounding vias around periphery of PCB)work?Are these the only two techniques at our disposal?MotivationMotivationMotivationMotivationMotivationMotivationMotivationMotivationTraces striplines(1),microstrips(2),and vias(3)and dielectric(4)areused to route time-varying curr

12、ents(digital signals,etc.)around on PCBs.Problem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem Definition(1)(2)(3)(4)Traces striplines(1),microstrips(2),and vias(3)and dielectric(4)areused to route time-varying currents(

13、digital signals,etc.)around on PCBs.Even if traces are not routed along the edge(5),radiation still occurs(6).Problem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem Definition(6)(1)(2)(3)(4)(5)Traces striplines(1),microst

14、rips(2),and vias(3)and dielectric(4)areused to route time-varying currents(digital signals,etc.)around on PCBs.Even if traces are not routed along the edge(5),radiation still occurs(6).We conclude currents in the traces create electromagnetic fields thatpropagate through the dielectric towards the e

15、dge(7).Problem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem Definition(6)(7)(1)(2)(3)(4)(5)Traces striplines(1),microstrips(2),and vias(3)and dielectric(4)areused to route time-varying currents(digital signals,etc.)arou

16、nd on PCBs.Even if traces are not routed along the edge(5),radiation still occurs(6).We conclude currents in the traces create electromagnetic fields thatpropagate through the dielectric towards the edge(7).If we understand how these fields are created,how they propagate to theedge,and how they radi

17、ate into the surrounding space once they get there,we can develop effective EMC guidelines to minimize radiation.Problem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem DefinitionProblem Definition(6)(7)(1)(2)(3)(4)(5)Stationary(Electrostat

18、ic)Fieldsi=dq/dt=0=charge at restOnly produce static E-fieldsExample:Charged capacitorVelocity(Magnetostatic)Fieldsi=dq/dt=constant(DC current)Only produce static H-fieldsExample:Solenoid connected to a batteryAccelerating Fieldsdi/dt=d2q/dt2 0Produce time-varying radiating electromagnetic fields 1,

19、2*Example:Any time varying current waveform*1,2 see references at end of presentationProblem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem Setup()()()()02000200011001()()0Note22()cossincossinsinc s:o nnnnnnnnndqnni taatbtadi tdqdi tnnnantbntdtTTadtdttnttn

20、db=+=+=Example:spectrum of 1 MHz 50%duty cycle 5 sec rise/fall time trapezoidal waveformProblem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem Setup Spectrum of digital signal currents produce radiating fields 3tan+=”+=dielectric damping losses +conduction

21、 losses,stored energy 4Problem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem SetupLosses in typical PCB dielectric increase with frequency.Attenuation of higher frequency harmonics distorts clock waveforms.Limits useable range of typical(inexpensive)PCBs

22、to 2 GHz.Attenuation acts like a natural“low pass filter”.Non-linear behavior requires discrete frequency modeling techniques.Problem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem Setup1-2 GHz sine waves good“compromise”modeling source.Fundamental harmoni

23、c of next generation CPUs.Still in useable range of typical PCB dielectrics.Can use existing FEM/FDTD programs that require constant ,”,.Problem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem SetupProblem SetupTo find fields we need to solve Maxwells two curl equations

24、.From current density,J,we can find E and H.From E and H we can determine propagation modes.From E x H(Poynting vector)we can find power properties.Power density of wave at different positions in PCB structures.Direction power is flowing(what happens inside and around a PCB).2(V/m)(A/m)(V/m)(A/m)(W/

25、m)xyzxyzttEEEHHH=+=+=+=HEEHExyzHxyzPE HJPhysics of PCB StructuresPhysics of PCB StructuresPhysics of PCB StructuresPhysics of PCB StructuresPhysics of PCB StructuresPhysics of PCB StructuresPhysics of PCB StructuresPhysics of PCB StructuresNumber of propagating modes in and around a PCBstructure.Sur

26、face waves propagate along the top and bottom surfaces of aPCB.TEM waves propagate along traces and between power/groundplanes.Ground/power planes-in conjunction with the impedancediscontinuities along the PCB edges-create resonant cavitiesthat support TE/TM modes.We need to understand how the struc

27、tures of a PCB cancreate and support these waves and modes before we candevelop and evaluate cost effective EMC solutions.Physics of PCB Structures(Surface Waves)Physics of PCB Structures(Surface Waves)Physics of PCB Structures(Surface Waves)Physics of PCB Structures(Surface Waves)Physics of PCB Str

28、uctures(Surface Waves)Physics of PCB Structures(Surface Waves)Physics of PCB Structures(Surface Waves)Physics of PCB Structures(Surface Waves)Surface waves propagate along reactive Z planes.9,10Originally predicted by Tesla.Formally developed by Uller(1903)and Zenneck(1907).If surface appears capaci

29、tive can support TEn(n=1,3,5,)modes.If surface appears inductive can support TMn(n=0,2,4,)modes.Dielectric over a ground plane(e.g.a PCB)can be made tolook like an inductive surface.xy00,rrField amplitude distribution normal to surfaceDirection of propagationPhysics of PCB Structures(Surface Waves)P

30、hysics of PCB Structures(Surface Waves)Physics of PCB Structures(Surface Waves)Physics of PCB Structures(Surface Waves)Physics of PCB Structures(Surface Waves)Physics of PCB Structures(Surface Waves)Physics of PCB Structures(Surface Waves)Physics of PCB Structures(Surface Waves)xy00,rrField amplitud

31、e distribution normal to surfaceDirection of propagationField decays exponentially in y direction.For thin coatings and long wavelengths(mm wavelengths),fielddecays slowly(extends far above the PCB).11Radiation from PCB edges can launch surface waves across PCBsurfaces.Physics of PCB Structures(TEM

32、Modes)Physics of PCB Structures(TEM Modes)Physics of PCB Structures(TEM Modes)Physics of PCB Structures(TEM Modes)Physics of PCB Structures(TEM Modes)Physics of PCB Structures(TEM Modes)Physics of PCB Structures(TEM Modes)Physics of PCB Structures(TEM Modes)Three kinds of PCB structures generate TEM

33、 mode waves.Microstrips:outer(visible)trace routed over a plane.Striplines:inner trace routed between two planes.Vias.MicrostripStriplineViaPhysics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of

34、 PCB(TEM Modes)Physics of PCB(TEM Modes)Fields in microstrips and striplines follow currents in trace.Relatively little energy propagates away from the trace.Some examples of|E x H|in a section of microstrip and stripline.Ground Planes Traces Current SourcesPhysics of PCB(TEM Modes)Physics of PCB(TE

35、M Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Fields in microstrips and striplines follow currents in trace.Relatively little energy propagates away from the trace.Some examples of|E x H|i

36、n a section of microstrip and stripline.Side ViewCross Section ViewTop View(microstrip)SourceSourcePhysics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)C

37、urrents on vias launch radial TEM waves into thedielectric planes.7E-field normal to ground planes(Ez).H-field circumferentially(H ).Wave impedance changes with radial distance from via.222dzrdztotalrzVE dIrHVE dZIrHdErH=Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Phys

38、ics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Physics of PCB(TEM Modes)Some examples of via induced power density fields.MicrostriptoMicrostripRadial waves from via propagating towards edge.Microstrip to microstrip routed through planes(Worst Offende

39、r)StriplinetoStriplinePhysics of PCB Structures(TE/TM Modes)Physics of PCB Structures(TE/TM Modes)Physics of PCB Structures(TE/TM Modes)Physics of PCB Structures(TE/TM Modes)Physics of PCB Structures(TE/TM Modes)Physics of PCB Structures(TE/TM Modes)Physics of PCB Structures(TE/TM Modes)Physics of P

40、CB Structures(TE/TM Modes)Conductive planes and impedance discontinuities alongedges can support TE and TM modes.Examples of TE(top)and TM(bottom)mode plane wavespropagating(bouncing back and forth)between two(infinite)conductive planes.8Physics of PCB Structures(TE/TM Resonant Modes)Physics of PCB

41、Structures(TE/TM Resonant Modes)Physics of PCB Structures(TE/TM Resonant Modes)Physics of PCB Structures(TE/TM Resonant Modes)Physics of PCB Structures(TE/TM Resonant Modes)Physics of PCB Structures(TE/TM Resonant Modes)Physics of PCB Structures(TE/TM Resonant Modes)Physics of PCB Structures(TE/TM R

42、esonant Modes)()2221,2cmnpfm n pabc=+In finite sized PCBs,ground planesand edges support TEmnp and TMmnpresonant modes at frequencies,fc.m,n,p=modes(0,1,2,3,)For a 12”x 12”PCB constructed with FR4 dielectric(r=4.5).()22210110,1,1217 MHz0.01012122cf=+=Physics of PCB Structures(TE/TM Resonant Modes)Ph

43、ysics of PCB Structures(TE/TM Resonant Modes)Physics of PCB Structures(TE/TM Resonant Modes)Physics of PCB Structures(TE/TM Resonant Modes)Physics of PCB Structures(TE/TM Resonant Modes)Physics of PCB Structures(TE/TM Resonant Modes)Physics of PCB Structures(TE/TM Resonant Modes)Physics of PCB Struc

44、tures(TE/TM Resonant Modes)Example of a double sided printed circuit board excited by a via.Edges left open(animation)Edges shorted(via fencing)(animation)Edge treatments impact radiation and resonance amplitudes.To start animation place mouse over animation region and click left mouse key once.Phys

45、ics of PCB Structures(Edge Effects)Physics of PCB Structures(Edge Effects)Physics of PCB Structures(Edge Effects)Physics of PCB Structures(Edge Effects)Physics of PCB Structures(Edge Effects)Physics of PCB Structures(Edge Effects)Physics of PCB Structures(Edge Effects)Physics of PCB Structures(Edge

46、Effects)Open edges behave like equivalent magnetic current sources.12Looks like a cross-section of a“Slot Antenna”Looks like a cross-section of a“Patch Antenna”.Edge treatments impact radiation and resonance amplitudes.Physics of PCBs (Summary)Physics of PCBs (Summary)Physics of PCBs (Summary)Physic

47、s of PCBs (Summary)Physics of PCBs (Summary)Physics of PCBs (Summary)Physics of PCBs (Summary)Physics of PCBs (Summary)Currents on vias(e.g.structures normal to power andground planes)are the dominant exitation mechanism.Propagation towards edges of radial electromagneticwaves are the dominant propa

48、gation mode.If the edges are left open can have significant radiation(same physical mechanism used in slot and pathantennas).If edges are shorted(via fences)PCB behaves like aresonant cavity.Motivation Problem definition Problem setup Physics of PCB propagation modes Physics of PCB edge effects Mini

49、mizing radiation from PCB edgesRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge EffectsRadiation from Edge Effectsin Printed Circuit Boards(PCBs)in Printed Circuit Boa

50、rds(PCBs)in Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)in Printed Circuit Boards(PCBs)First Rule of ThumbFirst Rule of ThumbFirst Rule of ThumbFirst Rule of ThumbFirst Rule of ThumbFirst Rule