24PCBDesignforRealworldEMIControl.ppt
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1、PCB Design for Real-World EMI ControlPrepared By Jia Wu Prepared By Jia Wu 2003-11-202003-11-202021/9/172021/9/171 1PCB Design for Real-World EMI ControlThe contents1.Introduce the EMC2.About the Basic EMC Design Intention 3.Introduce the Electromagnetic Induction4.The Myth of the Ground5.Introduce
2、the Return Current Route6.The Conclusions2021/9/172021/9/172 21.Introduce the EMC1.1 EMI and EMC concepts1.2 The source of EMI1.3 Introduce the Inductance1.4 Introduce the Ground1.5 Introduce the Shielding2021/9/172021/9/173 31.1.1 EMI conceptsEMI:Electromagnetic InterferenceEMI:Electromagnetic Inte
3、rference Any Any electromagnetic electromagnetic disturbance disturbance that that interrupts,interrupts,obstructs,obstructs,or or otherwise otherwise degrades degrades or or limits limits the the effective effective performance performance of of electronics/electrical electronics/electrical equipme
4、nt.equipment.It It can can be be induced induced intentionally intentionally and and unintentionally,unintentionally,as as a a result result of of spurious spurious emissions emissions and and responses,responses,intermodulation intermodulation products,products,and and the like.the like.2021/9/1720
5、21/9/174 4EMC:Electromagnetic Compatibility EMC:Electromagnetic Compatibility The condition which prevails when equipment is The condition which prevails when equipment is performing its individually designed function in a performing its individually designed function in a common electromagnetic env
6、ironment without common electromagnetic environment without causing or suffering unacceptable degradation causing or suffering unacceptable degradation due to unintentional electromagnetic interference due to unintentional electromagnetic interference to or from other equipment in the same to or fro
7、m other equipment in the same environment.environment.The ability of systems,equipment,and devices The ability of systems,equipment,and devices that utilize the electromagnetic spectrum to that utilize the electromagnetic spectrum to operate in their intended operational operate in their intended op
8、erational environments without suffering unacceptable environments without suffering unacceptable degradation or causing unintentional degradation degradation or causing unintentional degradation because of electromagnetic radiation or response.because of electromagnetic radiation or response.1.1.2
9、EMC concepts2021/9/172021/9/175 5EMC Structure Chart1.1.2 EMC concepts(Continue)Electromagnetic CompatibilityEMCInterference(EMI)Susceptibility(EMS)Conducted EmissionRadiatedEmissionConductedImmunityRadiatedImmunity2021/9/172021/9/176 61.2 The Source of EMIHigh speed clock generator;High speed bus s
10、ignal;Power node;Digital and Analog GND;I/O Cable and Connector2021/9/172021/9/177 71.3 Introduce the Inductance The inductance here is not only for the inductor.Inductance is critical for high speed signals.A voltage decrease will cause the change of Electromagnetic field.This change of intensity a
11、nd shape is a source of Emission.2021/9/172021/9/178 81.4 Introduce the GroundGround:The reference point.Different kinds of Ground should be separated from each others.Such as Earth reference,Power reference,Chassis reference.This can mitigate the interference between different signals and keep them
12、 pure.2021/9/172021/9/179 91.5 Introduce the ShieldingShielding is a useful way to limit EMI.Shielding is a useful way to limit EMI.n nThe magnitude of reflection loss depends on the ratio of barrier impedance to The magnitude of reflection loss depends on the ratio of barrier impedance to wave impe
13、dance,which in turn depends on its distance from the source and wave impedance,which in turn depends on its distance from the source and whether the field is electric or magnetic or whether it is a plane wave.whether the field is electric or magnetic or whether it is a plane wave.n nFor a slot with
14、a dimension equal to or less than a half-wave length,the For a slot with a dimension equal to or less than a half-wave length,the shielding effectiveness is:shielding effectiveness is:n nWhere l is maximum dimension of slot.Where l is maximum dimension of slot.2021/9/172021/9/1710101.5 Introduce the
15、 Shielding(Continue)1.5 Introduce the Shielding(Continue)2021/9/172021/9/1711112.Basic EMC Design Intention 2.1 The importance for EMC design2.2 Coupling Mechanisms2.3 Introduce the Signal Spectra2.4 Introduce the Resonance Effect2.5 Potential Interference Source2021/9/172021/9/1712122.1 The Importa
16、nce of EMC design1.EMC Design is important for cost-down.2.Need certificates to enter into different countries and regions,common marks:CCC-ChinaCE -European UnionVCCI-JapanBSMI-TaiwanFCC-United States2021/9/172021/9/1713132.2 Coupling MechanismsElectrical Field CouplingElectrical Field Coupling2021
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