Todd H. Hubing Clemson Vehicular Electronics Laboratory Clemson University

Transcription

1 How EMC Engineers use Computer Modeling Tools Productively Todd H. Hubing Clemson Vehicular Electronics Laboratory Clemson University

2 Modeling Software GEMACS 2

3 The Current State-of-the-Art Source: EMA Source: EMSS Source: CST Source: ANSYS Source: Huwin Source: Mentor Graphics Source: IndustrieHansa website 3

4 Two Important Points 1) Computer modeling tools (including numerical electromagnetic modeling codes) are valuable tools for EMC engineers. 4

5 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. 5

6 Modeling an Automotive Motor Driver Can we use electromagnetic modeling tools to identify and fix an electromagnetic interference problem? 6

7 Modeling a Straight Wire 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. 7

8 A rough estimate of the dominant EMI problem is more useful than a precise calculation of a negligible problem. 8

9 EMC Analysis Software Analytical Modeling Software specific geometries, closed-form equations limited scope, maximum convenience Numerical Modeling Software solves Maxwell s equations, accurate solutions to well-defined problems limited scope, requires expert user Design Rule Checkers review designs for rule violations that may result in problems very limited scope, maximum convenience Expert System / Maximum Emissions Calculators review designs for specific problem sources identify areas requiring a more careful evaluation estimate maximum possible emissions 9

10 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 10

11 Circuit Solvers Every EMC Engineer should have access to a basic SPICE-like circuit solver. 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. 11

12 Lumped-Element Modeling e.g. Crosstalk in Printed Circuit Board Traces C 12 R S1 R S2 + + V S1 V C R S2 11 C 22 R L2 V RL2 L1 V RL

13 Modeling Time-Domain RLC Circuits Circuit Board Nets Electrostatic Discharge Events 10 ohms 50 pf 7 pf 13

14 Modeling Non-Linear Behavior Transient protection Ferrites near saturation IC inputs near saturation 14

15 Transmission Line Modeling RS S1 l Z0 RL 15

16 Static Electric-Field Solvers A 2D or 3D static field solver is often the most useful computer modeling tool in an EMC Engineer s tool kit. 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 16

17 Calculating Mutual Capacitance * This is how several EM modeling companies got started. 17

18 Visualizing Fields Electric-Field Shielding 18

19 Visualizing Fields Guard Trace Effectiveness 19

20 Visualizing Fields Stacked Guard Trace Effectiveness 20

21 Calculating Imbalance Factor For microstrip trace structures, the imbalance parameter is given by, h C trace C trace C board where C trace and C board 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

22 Calculating Imbalance Factor 1.6 mm 1.6 mm 1.6 mm er = mm + V - Cable 1.7 mm 1.7 mm 1.7 mm Original Configuration wire diameter = 0.64 mm Use a 2-D static field solver to determine imbalance factor h = 0.03 h = V - Cable Equivalent Antenna-Mode Model V Cable = 0.3 V CM 22

23 Differential Source Driving a Twisted Wire Pair ACES Conference - March 24, 2014 T. Hubing 23

24 Single-Ended Source Driving a Twisted Wire Pair ACES Conference - March 24, 2014 T. Hubing 24

25 Single-Ended Source Driving a Twisted Wire Pair ACES Conference - March 24, 2014 T. Hubing 25

26 Sources Driving Shielded and Unshielded TWPs ACES Conference - March 24, 2014 T. Hubing 26

27 2-D and 2.5-D High-Frequency Field Solvers 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 Are much more efficient (i.e. faster and/or model more detail) Have a more intuitive user interface Less prone to numerical errors 27

28 2-D and 2.5-D High-Frequency Field Solvers Examples of 2-D and 2.5-D HF 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 28

29 3-D High-Frequency (Full Wave) Field Solvers 3-D full wave modeling codes are useful for: 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 29

30 3-D High-Frequency (Full Wave) Field Solvers 3-D full wave modeling codes are NOT useful for: Evaluating existing product designs Predicting EMC problems Troubleshooting EMC problems Validating EMI measurements of electronic devices 30

31 3-D High-Frequency (Full Wave) Field Solvers Modeling signal integrity problems Source: CST 31

32 3-D High-Frequency (Full Wave) Field Solvers Understanding how different structures can act as antennas 32

33 3-D High-Frequency (Full Wave) Field Solvers SAR Modeling Source is well-defined. Results are understood to be approximations Source: EMSS 33

34 3-D High-Frequency (Full Wave) Field Solvers Finding resonant frequencies of structures Source: NEC 34

35 Validating Maximum Radiated Emissions Calculations 5cm 5cm 20cm 20cm 1cm Spacing between heatsink and board is 1 cm 100 cm C heatsink C board 0.43 pf 5.14 pf 35

36 Key Point Computer models often yield incorrect results because: 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 36

37 Question posted to ResearchGate Answers included: BEM/MOM FDTD/FIT FEM (specific code) It depends My Answer: Source: ResearchGate website 37

38 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. 38

39 Design Rule Checkers Scan a board layout looking for design rule violations. Advantages Easier to understand what the software is doing Easier to use. 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 39

40 EMC Design Guideline Collection 40

41 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. 41

42 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. 42

43 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 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 43

44 What we are NOT doing 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. We NEVER do this. It is a bad idea now and always will be! T. Hubing 44

45 What we ARE doing SOURCE ANTENNA Identifying all possible sources, victims and coupling paths T. Hubing 45

46 Maximum Radiated Emissions Calculations 1 m l 46

47 Maximum Crosstalk Calculations and Measurements 47

48 Algorithms Locate Hard-to-Find Problems 48

49 Algorithms Locate Hard-to-Find Problems Type of Problem Identified Location of Problem Magnitude and Frequency of Problem 49

50 Algorithms Locate Hard-to-Find Problems U4 GRESET View of left half of board showing the problem nets. DATA2 U6 U1 U20 CONNECTOR P2 GRESET CONNECTOR P1 DATA2 50

51 Algorithms Locate Hard-to-Find Problems Type of Problem Identified Location of Problem Magnitude and Frequency of Problem 51

52 Algorithms Locate Hard-to-Find Problems Current-Driven Common-Mode Problem. U4 U1 U37 $1I6\CLKCPU CONNECTOR P2 $1I6\CLKCPU CONNECTOR P1 U19 52

53 Algorithms Locate Hard-to-Find Problems 53

54 Performance-Based EMC Design 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? 54

55 Computer Modeling Tools for EMC Engineers Rule Checkers Identify and Fix Potential EMC Problems Emissions Calculators / Expert Systems Numerical Modeling Tools 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. 55

56 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. 56