Predicting Emissions from Printed Circuit Boards or “ The

Predicting Emissions fromPredicting Emissions fromPrinted Circuit BoardsPrinted Circuit Boards

oror“The Quest for the Holy Grail”“The Quest for the Holy Grail”

Charles GrassoCharles GrassoStorageTekStorageTek

RMC EMC Symposium 1999

ContentsContents

n Prediction - The Holy Grailn Introduction to the Softwaren Description of Experimentn Modeling analysisn Data Comparisonn Conclusion


Prediction - The Holy Grail

nn The Product Designers Nightmare:The Product Designers Nightmare:––“Will my board pass the emissions test?”“Will my board pass the emissions test?”––“How big can the cooling holes be?”“How big can the cooling holes be?”––“How can I fix my EMC problem?”“How can I fix my EMC problem?”

nn Modeling Software can help.Modeling Software can help.


Ye Old EMC Design Strategy

Design itDesign itBuild itBuild itTest itTest it

Fix it -(cheaply?)Fix it -(cheaply?)Build new partsBuild new partsTest it AGAINTest it AGAIN

Ship it.Ship it.RMC EMC Symposium 1999

The NEW EMC Design Strategy

Design itDesign itSimulate itSimulate it

Build itBuild itTest it.Test it.Ship it.Ship it.


Field Solvers Can Save Timeand Money

nnUsing a solver we can createUsing a solver we can createmodels of components andmodels of components andperform subsystem and systemperform subsystem and systemlevel simulations as early aslevel simulations as early aspossible in the design cycle.possible in the design cycle.


What does a Field Solver do?What does a Field Solver do?


nn Solves Maxwell's Equations with specific Solves Maxwell's Equations with specificboundary conditions and defined materials.boundary conditions and defined materials.

nn Calculates and displays E, H fields. Calculates and displays E, H fields.nn Calculates and displays voltage and current Calculates and displays voltage and current

distributions.distributions.nn Calculates radiated fields. Calculates radiated fields.nn Calculates S-Parameters (allows use of Calculates S-Parameters (allows use of

physical physical structures as circuit elements)structures as circuit elements)

nn Performs automatic emissions test Performs automatic emissions test

Product Application

nn The benefits of Predictive Software:The benefits of Predictive Software:––Allows for analysis of sheet metal changes.Allows for analysis of sheet metal changes.––Analyze a printed wiring board before theAnalyze a printed wiring board before the

hardware is available.hardware is available.––Predict the emissions profile of a productPredict the emissions profile of a product

BEFORE the testBEFORE the test


Introduction to the Software

nn Ansoft HFSS (High Frequency StructureAnsoft HFSS (High Frequency StructureSimulator)Simulator)––Simulates arbitrary structures using FEMSimulates arbitrary structures using FEM––Full wave solver of Maxwell's EquationsFull wave solver of Maxwell's Equations––Can simulate an OATS experiment.Can simulate an OATS experiment.


Summary of FeaturesSummary of Features

nn Full-wave Finite Element MethodFull-wave Finite Element Methodnn Automatic Mesh Generation andAutomatic Mesh Generation and

Adaptive RefinementAdaptive Refinementnn Can compute near field and far fieldCan compute near field and far field

radiation patternsradiation patternsnn New Fast Frequency Sweep( New Fast Frequency Sweep(VerVer. 6). 6)


Adaptive MeshingAdaptive Meshing

Initial Mesh Final Mesh

2746 Tetrahedrons3 Adaptive Passes

1547 Tetrahedrons WR 90 waveguide f = 10 GHz∆s = 0.01


Ansoft HFSS Solver:Ansoft HFSS Solver:Adaptive SolutionAdaptive Solution

Create InitialMesh

Calculate ElectricFields

CalculateS-Parameters

DisplayS-Parameters

and Fields

Refine Mesh∆S Acceptable?No

Yes

Perform FrequencySweep

Initial

Second

Final

Calibration

nn Predictive Software:Predictive Software:––2D structures are easy to calibrate.2D structures are easy to calibrate.

nn MicrostripMicrostripnn Two wire structuresTwo wire structures

––How to calibrate the EME softwareHow to calibrate the EME softwarecapability?capability?


Description of Experiment

From: R.W. Dockey, Asymmetrical Mode Radiation from Multilayer Printed Circuit Boards EMC/ESD International Symposium, Denver 1992.

SMA ConnectorGround Plane

50 ohm trace 50 ohm resistorFR4 substrate

Side View

Top View

50 ohm trace 50 ohm resistor


The Physics of Radiation

Signal Source

Ground Plane

Signal Trace

Load

DifferentialCurrent Flow

Vg

Ls Lm

Ls Lm


Experiment Results

From: R.W. Dockey, Asymmetrical Mode Radiation from Multilayer Printed Circuit Boards EMC/ESD International Symposium, Denver 1992.

120mm x 280mm Standard PCB Without Cables

0

10

20

30

40

50

60

0 100 200 300 400 500 600 700 800 900 1000

Frequency (MHz)

Fiel

d S

tren

gth

(dB

uV/m

)

Field Strength

FCC Class B


The Experiment Model


Simulation Results


Data Comparison

nn Below PWB Cutoff Frequency -Below PWB Cutoff Frequency -––Data tracks very well in amplitude andData tracks very well in amplitude and

delta.delta.––At 200MHz:At 200MHz:

–– Measured data - 30dBuVMeasured data - 30dBuV–– Simulation - 27dBuVSimulation - 27dBuV–– ∆∆ Measured data - 12dB/100MHz Measured data - 12dB/100MHz–– ∆∆ Simulation - 13dB/100MHz Simulation - 13dB/100MHz


Data Comparison

nn At PWB Cutoff FrequencyAt PWB Cutoff Frequency––Measured Data = 360MHzMeasured Data = 360MHz––Simulation = 400MHzSimulation = 400MHz––Calculation = 402 MHzCalculation = 402 MHz


Data Comparison

nn At PWB Cutoff Frequency:At PWB Cutoff Frequency:––Actual Data = 47dBuVActual Data = 47dBuV––Simulation = 49dBuVSimulation = 49dBuV

nn Above PWB Cutoff Frequency -Above PWB Cutoff Frequency -––Actual data (@1000MHz) = 46dBuVActual data (@1000MHz) = 46dBuV––Simulation = 49dBuVSimulation = 49dBuV


EM Modeling Capabilities:EM Modeling Capabilities:

nn We canWe can–– Model 2d structuresModel 2d structures

nn Fibre Channel OddFibre Channel OddMode ImpedancesMode Impedances

–– Model 3d structuresModel 3d structuresnn Traces over planesTraces over planesnn ViasViasnn R/W Head FieldsR/W Head Fields


EM Modeling Capabilities:EM Modeling Capabilities:

nn We will be able toWe will be able topredict radiatedpredict radiatedemissions from:emissions from:–– boardsboards–– enclosuresenclosures–– cablescables


ConclusionConclusion

nn Analysis software CAN be used toAnalysis software CAN be used topredict the emissions characteristics ofpredict the emissions characteristics ofa circuit board.a circuit board.

nn Calibration of the software is essentialCalibration of the software is essentialto ensure accurate application.to ensure accurate application.


Finally….


Documents

Predicting Emissions from Printed Circuit Boards or “ The