how emc engineers use computer modeling tools productively
TRANSCRIPT
How EMC Engineers use Computer Modeling Tools Productively
Todd H. Hubing Clemson Vehicular Electronics Laboratory
Clemson University
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Modeling Software
GEMACS
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The Current State-of-the-Art
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Source: IndustrieHansa website
Source: EMA
Source: ANSYS
Source: CST
Source: Huwin
Source: Mentor Graphics
Source: EMSS
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Two Important Points
1) Computer modeling tools (including numerical electromagnetic modeling codes) are valuable tools for EMC engineers.
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Two Important Points
1) Computer modeling tools (including numerical electromagnetic modeling codes) are valuable tools for EMC engineers.
2) Numerical electromagnetic modeling codes are NOT useful for identifying and solving EMC problems.
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Modeling an Automotive Motor Driver
Can we use electromagnetic modeling tools
to identify and fix
an electromagnetic
interference problem?
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Modeling a Straight Wire
http://www.cvel.clemson.edu/modeling/software/
Even simple geometries are
difficult to model using most
commercial tools.
Software attempts to model
configurations that it can’t
model.
Geometries analyzed are
not always the what the user is
led to believe.
Users must understand EM
theory.
Users must be familiar with
the limitations of the particular
technique.
Users must be familiar with
the peculiarities of the software
and its user interface.
Even simple geometries are
difficult to model using most
commercial tools.
Software attempts to model
configurations that it can’t
model.
Geometries analyzed are
not always the what the user is
led to believe.
Users must understand EM
theory.
Users must be familiar with
the limitations of the particular
technique.
Users must be familiar with
the peculiarities of the software
and its user interface.
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A rough estimate of the dominant EMI problem is
more useful than a precise calculation of a negligible
problem.
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EMC Analysis Software
Analytical Modeling Software
Numerical Modeling Software
Design Rule Checkers
Expert System / Maximum Emissions Calculators
specific geometries, closed-form equations limited scope, maximum convenience
solves Maxwell’s equations, accurate solutions to well-defined problems limited scope, requires expert user
review designs for rule violations that may result in problems very limited scope, maximum convenience
review designs for specific problem sources identify areas requiring a more careful evaluation estimate maximum possible emissions
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EM Modeling Software
Circuit and Transmission Line Solvers
2D and 3D Static Field Solvers
2D and “2.5 D” HF Field Solvers
3D HF (Full-Wave) Field Solvers
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Circuit Solvers
Help’s engineers to intuitively understand how intentional and unintentional currents propagate.
For lumped-element modeling of signal paths and coupling paths.
For time-domain modeling of RLC equivalent circuits.
For modeling non-linear behavior of components and circuits.
Every EMC Engineer should have access to a basic SPICE-like circuit solver.
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Lumped-Element Modeling
VS1
VS2
RS1
RS2
RL1R
L2 VRL2
VRL1
+ +
--
C11
C12
C22
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e.g. Crosstalk in Printed Circuit
Board Traces
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Modeling Time-Domain RLC Circuits
50 pF
10 ohms
7 pF
Circuit Board Nets
Electrostatic Discharge Events
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Modeling Non-Linear Behavior
Transient protection
Ferrites near saturation
IC inputs near saturation
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Transmission Line Modeling RS
Z0
lS1
RL
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Static Electric-Field Solvers
Estimating mutual capacitance of structures
Help’s engineers to visualize electric fields
This is an essential skill for EMC engineers and HF board designers.
Evaluating effectiveness of electric-field shields
Calculating “balance factor”
A 2D or 3D static field solver is often the most useful computer modeling
tool in an EMC Engineer’s tool kit.
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Calculating Mutual Capacitance
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This is how several EM modeling companies got started.
*
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Visualizing Fields
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Electric-Field Shielding
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Visualizing Fields
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Guard Trace Effectiveness
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Visualizing Fields
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Stacked Guard Trace Effectiveness
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Calculating Imbalance Factor
trace
trace board
ChC C
For microstrip trace structures, the imbalance parameter is given by,
where Ctrace and Cboard are the stray capacitances per unit length of the signal trace and the ground plane, respectively.
T. Watanabe, H. Fujihara, O. Wada, Y. Toyota, R. Koga, and Y. Kami, “A prediction method of common-mode excitation on a printed circuit board having a signal trace near the ground edge,” IEICE Trans. Commun. vol. E87-B, no. 8, Aug. 2004.
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Calculating Imbalance Factor
VCable
+
-
1.6 mm1.6 mm 1.6 mm
1.6 mmer = 4
1.7 mm
wire diameter = 0.64 mm
1.7 mm 1.7 mm
VCable
+
-
V = 0.3 VCable CM
h = 0.03
h = 0.33
Original Configuration
Equivalent Antenna-Mode Model
Use a 2-D static field solver to
determine imbalance
factor
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Differential Source Driving a Twisted Wire Pair
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Single-Ended Source Driving a Twisted Wire Pair
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Single-Ended Source Driving a Twisted Wire Pair
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Sources Driving Shielded and Unshielded TWPs
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2-D and “2.5-D” High-Frequency Field Solvers
Are much more efficient (i.e. faster and/or model more detail)
Have a more intuitive user interface
Less prone to numerical errors
High-Frequency field solvers are generally not capable of modeling static fields, but 2-D and 2.5-D tools have several advantages when compared to 3D Full-Wave field solvers. Generally, they …
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2-D and “2.5-D” High-Frequency Field Solvers
2D tools for modeling axi-symmetric 3D configurations
2D tools for modeling PCB cross-sections
2.5-D tools for modeling PCB traces in layered media
Examples of 2-D and 2.5-D HF field solvers:
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3-D High-Frequency (Full Wave) Field Solvers
Learning about EM wave propagation
Understanding how different structures can act as antennas
Modeling the behavior of circuit components and packages
Developing and validating other types of models
Validating measurements of well defined source configurations
3-D full wave modeling codes are useful for:
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3-D High-Frequency (Full Wave) Field Solvers
Evaluating existing product designs
Predicting EMC problems
Troubleshooting EMC problems
Validating EMI measurements of electronic devices
3-D full wave modeling codes are NOT useful for:
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3-D High-Frequency (Full Wave) Field Solvers
Modeling signal integrity problems
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Source: CST
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3-D High-Frequency (Full Wave) Field Solvers
Understanding how different structures can act as antennas
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3-D High-Frequency (Full Wave) Field Solvers
SAR Modeling
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Source is well-defined.
Results are understood to be approximations
Source: EMSS
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3-D High-Frequency (Full Wave) Field Solvers
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Source: NEC
Finding resonant frequencies of structures
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Validating Maximum Radiated Emissions Calculations
heatsink
board
0.43 pF
5.14 pF
C
C
20cm 20cm
10
0 cm
5cm 5cm
1cm
Spacing between heatsink and board is 1 cm
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Key Point
Software was not capable of analyzing the input configuration
Software defaults were inappropriate for the problem
The input was not exactly what the user thought
Results were misinterpreted by the user
Computer models often yield incorrect results because:
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Question posted to ResearchGate
Source: ResearchGate website
BEM/MOM
FDTD/FIT
FEM (specific code)
It depends
Answers included:
My Answer:
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Summary
• Numerical EM modeling tools require the user to be familiar
with EM theory, the limitations of the techniques being
applied, and the limitations of the particular software
implementation.
• Numerical EM modeling tools should only be trusted when
the solutions can be confirmed by other methods.
• Numerical EM modeling tools are NOT particularly useful for
the design and troubleshooting of digital electronics
products.
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Advantages – Easier to understand what the software is doing
Easier to use.
Scan a board layout looking for design rule violations.
Disadvantages – Design rules don’t apply in all situations
Higher board cost to meet unnecessary design rules
Will not detect problems that don’t violate a pre-defined rule
Designing to comply with design rules produces terrible designs
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Design Rule Checkers
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EMC Design Guideline Collection
http://www.learnemc.com/tutorials/guidelines.html
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What is a PCB EMC Expert System?
EMC Expert System software should work with automated printed circuit
board layout tools to:
review and analyze printed circuit board designs;
point out problems with the layout;
estimate levels of radiated EMI;
anticipate ESD and radiated susceptibility problems; and
provide circuit and board layout design advice.
Using the same general approach that human experts would use.
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What is a PCB Expert System?
The goal is not to provide an accurate estimate of
radiated emission levels or to preclude the
necessity of testing the final product.
The goal is to distinguish between a good design
and a bad design and identify features of a design
that are likely to result in emissions or
susceptibility problems.
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EMC Requirements and Key Design Considerations for Automotive Systems and Components
Radiated Emissions Radiated
Susceptibility Transient Immunity
Electrostatic Discharge
Bulk Current Injection
• 1 HF GND
• Risetime Control
• Filtered I/O
• Adequate Decoupling
• Balance Control
• 1 HF GND
• Filtered I/O
• Adequate Decoupling
• Balance Control
• LF Current Path Control
• Chassis GND on board
• Filtered I/O
• Adequate Decoupling
• LF Current Path Control
• Chassis GND on board
• Filtered I/O
• Adequate Decoupling
• 1 HF GND
• Chassis GND on board
• Filtered I/O
• Adequate Decoupling
• Balance Control
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In 2011, CVEL began to guarantee that the automotive products they reviewed/designed would meet all automotive EMC
requirements the first time they were tested.
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What we are NOT doing
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We NEVER do this. It is a bad idea now and always will be!
We are NOT modeling the circuit boards, enclosures , cables and test set-up, then calculating the radiated emissions.
We don’t want to know how much a given configuration will radiate. The answer to that question depends on a lot of factors that we have no control over. We want to know if our product will meet its requirements.
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What we ARE doing
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Identifying all possible sources, victims and coupling paths
SOURCE ANTENNA
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Maximum Radiated Emissions Calculations
l
1 m
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Maximum Crosstalk Calculations and Measurements
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Algorithms Locate Hard-to-Find Problems
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Algorithms Locate Hard-to-Find Problems
Type of Problem Identified
Location of Problem Magnitude and Frequency of Problem
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Algorithms Locate Hard-to-Find Problems
View of left half of
board showing the
problem nets.
GRESET GRESET
GRESET GRESET
DATA2 DATA2
DATA2 DATA2 CONNECTOR P1 CONNECTOR P1
CONNECTOR CONNECTOR P2 P2
U4 U4
U20 U20
U1 U1 U6 U6
GRESET
GRESET
DATA2
DATA2 CONNECTOR P1
CONNECTOR P2
U4
U20
U1 U6
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Algorithms Locate Hard-to-Find Problems
Type of Problem Identified
Location of Problem Magnitude and Frequency of Problem
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Algorithms Locate Hard-to-Find Problems
$1I6\CLKCPU
CONNECTOR P1
CONNECTOR
P2
U4
U1
$1I6\CLKCPU
U19
U37
Current-Driven Common-Mode Problem.
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Algorithms Locate Hard-to-Find Problems
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Performance-Based EMC Design
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Design decision based on actual EMC performance requirements.
Answers questions such as:
- Is this decoupling adequate? - Can this trace cross over a gap in the ground plane? - Do I need a shielded enclosure? - How many ground wires are required in this cable? - Can I violate “this” design rule?
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Computer Modeling Tools for EMC Engineers
Rule Checkers
Emissions Calculators / Expert Systems
Numerical Modeling Tools
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Identify and Fix Potential EMC Problems
Analyze well-defined structures to:
1. validate results obtained by other means, or
2. Learn about the general behavior of fields or currents in these structures.
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For More Information:
List of “free” EM
modeling codes.
List of commercial EM
modeling codes.
Info on EM modeling
techniques.
Info on EM modeling
software.
Prototype MR EMC
calculator.
http://www.cvel.clemson.edu/modeling http://www.cvel.clemson.edu/modeling
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