The problem with electromagnetic compatibility (EMC) is not the difficulty of calculating the emissions from any particular radiating structure. The problem is much more one of recognizing the various types of radiating modes, deciding which is the worst case, and then knowing how to fix it. Identifying the worst-case radiating mode is quite important, because any problem you fix that isn't the worst-case mode makes zero difference to your compliance.

Don't expect anybody's software to tell you what is going to be the worst-case radiating mode in your design. Experts can't even do that. [135]

[135] Put any three EMC specialists in a room, have them review your design, and ask them to agree on what is the most significant flaw. Don't interpret the resulting conflagration as a reflection of their skill; merely accept it as an indication of the difficulty of the problem.

The ability to discover which is the worst offender is 90% of the battle. Once the worst source is identified and fixed, the second-worst source looms as the next problem. For a product that is 20 dB out of spec, there may be 10 different fixes, each worth 2 to 3 dB, required to fully address all the problems. It's a long, serial process.

13.8.1 EMC Simulation

## Article first published in EDN Magazine , March 2, 1998Let me give you some advice: Real live EMI problems are much too complex for even the best software tools. As much as I wish the situation weren't true, at this point the best tool is still experience. Many aspects of the EMI problem make prediction a difficult task, especially when working at the system level. First, the process involves simulation of 3-D wave patterns over a rather large area. That is, your computer is going to spend a lot of time grinding numbers to get even the most rudimentary results. Second, every bit of metal in the product matters: every via, trace, pad, bonding wire, connector, and cable. Many times, the system parts you choose not to include in the model turn out to be the very ones that create the worst EMI headaches . That's the nature of the problem. You seldom know beforehand what parts of a system will turn out to be the worst EMI offenders. Third, EMI is a strong function of switching speed, data patterns, and precise data timing. That's right, data patterns and timing. If you don't believe me, find out what kind of software people ship to the EMI test range ”some companies send several versions to see which works best. EMI problems are much too complex for even the best software tools. The EMI problem is so complex, it's na ve to think you can just type in a few parameters and get meaningful results. For example, how should you model the split-plane zone on a mixed 3.3V/2.5V processor board? Obviously, the board stack-up, the shape of the 3.3V and 2.5V regions , and the trace layout matter. Did you realize that the placement and layout of bypass capacitors will markedly influence the result? How about power supply noise? You'd have to model the power supply noise, including phase, at all frequencies from 30 MHz through several GHz to get meaningful answers. Oops, that would be a function of the software running on the board, wouldn't it? Guess you'll have to model that too. Now add little features such as power supply wiring. It is well known that enclosing your power supply wiring in a good metal conduit can reduce radiation from the wiring. How would you like to spend your Easter break modeling the contact resistance and inductance of the screws used to hold the conduit in place? Get the picture? You can't model everything. It's too complex. You can't leave anything out, either, because you never fully know what is going to matter. So, what can you do? Apply these time- tested , common-sense rules: **Limit your risetimes where practicable.**- Use your experience. If last year's design ran at speed x , and today you are planning to do 2 x , you are likely to need another 6 dB of protection.
- Run a quick EMI scan as early as possible.
The most promising new EMI tools will be more like expert systems than simulators. They will give you advice and provide reference information, but they won't make rash predictions . If these tools are worth their salt, the first three bits of advice they will provide are listed in 1, 2, and 3 above. |

POINT TO REMEMBER

- Real live EMI problems are much too complex for even the best software tools.

Fundamentals

- Impedance of Linear, Time-Invariant, Lumped-Element Circuits
- Power Ratios
- Rules of Scaling
- The Concept of Resonance
- Extra for Experts: Maximal Linear System Response to a Digital Input

Transmission Line Parameters

- Transmission Line Parameters
- Telegraphers Equations
- Derivation of Telegraphers Equations
- Ideal Transmission Line
- DC Resistance
- DC Conductance
- Skin Effect
- Skin-Effect Inductance
- Modeling Internal Impedance
- Concentric-Ring Skin-Effect Model
- Proximity Effect
- Surface Roughness
- Dielectric Effects
- Impedance in Series with the Return Path
- Slow-Wave Mode On-Chip

Performance Regions

- Performance Regions
- Signal Propagation Model
- Hierarchy of Regions
- Necessary Mathematics: Input Impedance and Transfer Function
- Lumped-Element Region
- RC Region
- LC Region (Constant-Loss Region)
- Skin-Effect Region
- Dielectric Loss Region
- Waveguide Dispersion Region
- Summary of Breakpoints Between Regions
- Equivalence Principle for Transmission Media
- Scaling Copper Transmission Media
- Scaling Multimode Fiber-Optic Cables
- Linear Equalization: Long Backplane Trace Example
- Adaptive Equalization: Accelerant Networks Transceiver

Frequency-Domain Modeling

- Frequency-Domain Modeling
- Going Nonlinear
- Approximations to the Fourier Transform
- Discrete Time Mapping
- Other Limitations of the FFT
- Normalizing the Output of an FFT Routine
- Useful Fourier Transform-Pairs
- Effect of Inadequate Sampling Rate
- Implementation of Frequency-Domain Simulation
- Embellishments
- Checking the Output of Your FFT Routine

Pcb (printed-circuit board) Traces

- Pcb (printed-circuit board) Traces
- Pcb Signal Propagation
- Limits to Attainable Distance
- Pcb Noise and Interference
- Pcb Connectors
- Modeling Vias
- The Future of On-Chip Interconnections

Differential Signaling

- Differential Signaling
- Single-Ended Circuits
- Two-Wire Circuits
- Differential Signaling
- Differential and Common-Mode Voltages and Currents
- Differential and Common-Mode Velocity
- Common-Mode Balance
- Common-Mode Range
- Differential to Common-Mode Conversion
- Differential Impedance
- Pcb Configurations
- Pcb Applications
- Intercabinet Applications
- LVDS Signaling

Generic Building-Cabling Standards

- Generic Building-Cabling Standards
- Generic Cabling Architecture
- SNR Budgeting
- Glossary of Cabling Terms
- Preferred Cable Combinations
- FAQ: Building-Cabling Practices
- Crossover Wiring
- Plenum-Rated Cables
- Laying Cables in an Uncooled Attic Space
- FAQ: Older Cable Types

100-Ohm Balanced Twisted-Pair Cabling

- 100-Ohm Balanced Twisted-Pair Cabling
- UTP Signal Propagation
- UTP Transmission Example: 10BASE-T
- UTP Noise and Interference
- UTP Connectors
- Issues with Screening
- Category-3 UTP at Elevated Temperature

150-Ohm STP-A Cabling

- 150-Ohm STP-A Cabling
- 150- W STP-A Signal Propagation
- 150- W STP-A Noise and Interference
- 150- W STP-A: Skew
- 150- W STP-A: Radiation and Safety
- 150- W STP-A: Comparison with UTP
- 150- W STP-A Connectors

Coaxial Cabling

- Coaxial Cabling
- Coaxial Signal Propagation
- Coaxial Cable Noise and Interference
- Coaxial Cable Connectors

Fiber-Optic Cabling

- Fiber-Optic Cabling
- Making Glass Fiber
- Finished Core Specifications
- Cabling the Fiber
- Wavelengths of Operation
- Multimode Glass Fiber-Optic Cabling
- Single-Mode Fiber-Optic Cabling

Clock Distribution

- Clock Distribution
- Extra Fries, Please
- Arithmetic of Clock Skew
- Clock Repeaters
- Stripline vs. Microstrip Delay
- Importance of Terminating Clock Lines
- Effect of Clock Receiver Thresholds
- Effect of Split Termination
- Intentional Delay Adjustments
- Driving Multiple Loads with Source Termination
- Daisy-Chain Clock Distribution
- The Jitters
- Power Supply Filtering for Clock Sources, Repeaters, and PLL Circuits
- Intentional Clock Modulation
- Reduced-Voltage Signaling
- Controlling Crosstalk on Clock Lines
- Reducing Emissions

Time-Domain Simulation Tools and Methods

- Ringing in a New Era
- Signal Integrity Simulation Process
- The Underlying Simulation Engine
- IBIS (I/O Buffer Information Specification)
- IBIS: History and Future Direction
- IBIS: Issues with Interpolation
- IBIS: Issues with SSO Noise
- Nature of EMC Work
- Power and Ground Resonance

Points to Remember

Appendix A. Building a Signal Integrity Department

Appendix B. Calculation of Loss Slope

Appendix C. Two-Port Analysis

- Appendix C. Two-Port Analysis
- Simple Cases Involving Transmission Lines
- Fully Configured Transmission Line
- Complicated Configurations

Appendix D. Accuracy of Pi Model

Appendix E. erf( )

Notes

High-Speed Signal Propagation[c] Advanced Black Magic

ISBN: 013084408X

EAN: N/A

EAN: N/A

Year: 2005

Pages: 163

Pages: 163

- Chapter V Consumer Complaint Behavior in the Online Environment
- Chapter VI Web Site Quality and Usability in E-Commerce
- Chapter XV Customer Trust in Online Commerce
- Chapter XVI Turning Web Surfers into Loyal Customers: Cognitive Lock-In Through Interface Design and Web Site Usability
- Chapter XVIII Web Systems Design, Litigation, and Online Consumer Behavior

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