how emc engineers use computer modeling tools productively

How EMC Engineers use Computer Modeling Tools Productively

Todd H. Hubing Clemson Vehicular Electronics Laboratory

Clemson University

ACES Conference - March 24, 2014 T. Hubing 2

Modeling Software

GEMACS

ACES Conference - March 24, 2014 3

The Current State-of-the-Art

T. Hubing

Source: IndustrieHansa website

Source: EMA

Source: ANSYS

Source: CST

Source: Huwin

Source: Mentor Graphics

Source: EMSS


Two Important Points

1) Computer modeling tools (including numerical electromagnetic modeling codes) are valuable tools for EMC engineers.

T. Hubing


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.

T. Hubing


Modeling an Automotive Motor Driver

Can we use electromagnetic modeling tools

to identify and fix

an electromagnetic

interference problem?


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.


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.


the limitations of the particular

technique.


the peculiarities of the software

and its user interface.

T. Hubing


A rough estimate of the dominant EMI problem is

more useful than a precise calculation of a negligible

problem.


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

T. Hubing


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

T. Hubing


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.

T. Hubing


Lumped-Element Modeling

VS1

VS2

RS1

RS2

RL1R

L2 VRL2

VRL1

+ +

--

C11

C12

C22

T. Hubing

e.g. Crosstalk in Printed Circuit

Board Traces


Modeling Time-Domain RLC Circuits

50 pF

10 ohms

7 pF

Circuit Board Nets

Electrostatic Discharge Events

T. Hubing


Modeling Non-Linear Behavior

Transient protection

Ferrites near saturation

IC inputs near saturation

T. Hubing


Transmission Line Modeling RS

Z0

lS1

RL

T. Hubing


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.

T. Hubing


Calculating Mutual Capacitance

T. Hubing

This is how several EM modeling companies got started.

*


Visualizing Fields

T. Hubing

Electric-Field Shielding


Visualizing Fields

T. Hubing

Guard Trace Effectiveness


Visualizing Fields

T. Hubing

Stacked Guard Trace Effectiveness


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.

T. Hubing


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

23

Differential Source Driving a Twisted Wire Pair

ACES Conference - March 24, 2014 T. Hubing

24

Single-Ended Source Driving a Twisted Wire Pair


25

Single-Ended Source Driving a Twisted Wire Pair


26

Sources Driving Shielded and Unshielded TWPs



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 …

T. Hubing


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:

T. Hubing


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:

T. Hubing



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:

T. Hubing



Modeling signal integrity problems

T. Hubing

Source: CST



Understanding how different structures can act as antennas

T. Hubing



SAR Modeling

T. Hubing

Source is well-defined.

Results are understood to be approximations

Source: EMSS



T. Hubing

Source: NEC

Finding resonant frequencies of structures


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

T. Hubing


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:

T. Hubing


Question posted to ResearchGate

Source: ResearchGate website

BEM/MOM

FDTD/FIT

FEM (specific code)

It depends

Answers included:

My Answer:


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.

T. Hubing

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


Design Rule Checkers

T. Hubing


EMC Design Guideline Collection

http://www.learnemc.com/tutorials/guidelines.html

T. Hubing


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.

T. Hubing


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.

T. Hubing

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


• Balance Control

• LF Current Path Control

• Chassis GND on board

• Filtered I/O


• LF Current Path Control


• Filtered I/O


• 1 HF GND


• Filtered I/O


• Balance Control

43

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.

ACES Conference - March 24, 2014

T. Hubing

What we are NOT doing

44

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.

T. Hubing

What we ARE doing

45

Identifying all possible sources, victims and coupling paths

SOURCE ANTENNA

T. Hubing


Maximum Radiated Emissions Calculations

l

1 m

T. Hubing


Maximum Crosstalk Calculations and Measurements

T. Hubing


Algorithms Locate Hard-to-Find Problems

T. Hubing



Type of Problem Identified

Location of Problem Magnitude and Frequency of Problem

T. Hubing



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

T. Hubing



Type of Problem Identified

Location of Problem Magnitude and Frequency of Problem

T. Hubing



$1I6\CLKCPU

CONNECTOR P1

CONNECTOR

P2

U4

U1

$1I6\CLKCPU

U19

U37

Current-Driven Common-Mode Problem.

T. Hubing



T. Hubing

Performance-Based EMC Design

54

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?


Computer Modeling Tools for EMC Engineers

Rule Checkers

Emissions Calculators / Expert Systems

Numerical Modeling Tools

T. Hubing

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.


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

T. Hubing

how emc engineers use computer modeling tools productively

Documents