Electronic Systems Design for EMC Compliance

Description

Well-designed electronic systems operate reliably in their intended electromagnetic environment. These systems are not affected by voltage spikes on their power or signal lines; they function normally in the presence of strong electric or magnetic fields; and the systems’ own fields do not interfere with other systems nearby. In a well-designed system, the cost of grounding, shielding and filtering is usually a negligible percentage of the overall system component costs. Unfortunately, many electronic systems are not well designed. It is not unusual for a company to spend millions of dollars and thousands of man-hours attempting to track down and correct system malfunctions that are the direct result of improper grounding and shielding. This course reviews the fundamental grounding, filtering and shielding concepts that all engineers can utilize to ensure the safety and reliability of their products at the lowest possible cost.

Today's rapid development cycles require products to meet their EMC requirements the first time they come into the lab for testing. Board layout changes and other EMC "fixes" can significantly add to the cost of a product and/or delay its development schedule. First-pass compliance with EMC requirements starts with the circuit board layout. Printed circuit board layout is often the single most important factor affecting the electromagnetic compatibility of electronic systems. Boards that are auto-routed or laid out according to a list of “design rules” do not usually meet electromagnetic compatibility requirements on the first pass; and the products using these boards are more likely to require expensive fixes such as ferrites on cables or shielded enclosures. Taking the time to ensure that components are properly placed, transition times are not left to chance, and traces are optimally routed will generally result in products that meet all electromagnetic compatibility and signal integrity requirements on time and on budget.

Many electronic systems employ mixed-signal boards (boards with both analog and digital circuits). Mixed-signal boards require that special attention be paid to the routing of the low-frequency currents. Minor mistakes in the layout of these boards can mean the difference between a reliable product and a product with severe EMC problems.

The cables that carry power and signals to and from the system, or between boards in a system, are another key design consideration. Shielded cables are not always better than unshielded cables, and choosing the right cable for the right application can be as important as circuit board design and layout for ensuring that a product will be cost effective and meet all EMC requirements.

This course stresses the fundamental concepts and tools that electronics engineers can employ to avoid electromagnetic compatibility and signal integrity problems. Students completing the course will be able to make good decisions regarding board layout and system design for EMC. They will also be introduced to tools and techniques for quickly reviewing designs in order to flag potential problems well before the first hardware is built and tested.

Course Outline

Day 1 - Important Fundamental Concepts

1. Introduction
   • Overview of Electromagnetic Compatibility Failure Mechanisms
   • Examples of Good and Bad System Designs
2. Signal Routing and Termination
   • Tracing Current Paths
   • Concept of Least Impedance
   • To Match or Not to Match
   • Balanced or Unbalanced
   • Transition Time Control
   • Signal Integrity
3. Identifying the Unintentional Antennas on a Board
   • Essential Elements of an Antenna
   • The Wire Harness
   • The Chassis/Enclosure
4. Noise Sources and Coupling Mechanisms
   • Integrated Circuits as Sources of EMI
   • Parasitic Oscillations and Unexpected Noise Sources
   • ESD and Transient Susceptibility
   • Conducted, Electric and Magnetic Field Coupling
5. Grounding, Filtering and Shielding
   • Ground vs. Signal Return
   • Grounding on Mixed-Signal Boards
   • Effective and Ineffective Filtering
   • Filters that Work Above 100 MHz
   • Effective and Ineffective Shielding
   • Transient Protection
6. DC Power Distribution and Decoupling
   • Effective Power Distribution Strategies
   • Choosing and Locating Decoupling Capacitors
   • Low-Inductance Capacitor Connections
   • Isolating PLLs and Other Sensitive Devices
7. Strategies for PCB Layout
   • Design Guidelines (Good and Bad)
   • Optimizing Component Placement
   • Stack-up and Routing Priorities
   • Common Problems that are Easily Avoided

Day 2 - Design Tools and Techniques

1. Key System-Level Design Considerations
   • For Radiated Emissions Tests
   • For Conducted Emissions Tests
   • For Radiated Susceptibility
   • For ESD and Transient Tests
2. Design Review Steps and Examples
   • Which Circuits or Nets Deserve Attention?
   • Which Transition Times Require Control?
   • Which Current Paths need to be Traced?
   • Which Nets Have a Balance Mismatch (and does it matter)?
   • Where are the Antennas?
   • Where will ESD and Transient Currents Flow?
   • What's the Worst That Could Happen?
3. Tools of the Trade
   • Schematic and Board Layout Tools
   • Circuit Solvers
   • Field Solvers
   • Full-Wave Modeling Tools
   • Design Rule Checkers
   • Maximum Emissions/Coupling Calculators
4. Specific Design Examples
   • Printer Control Circuit
   • Wireless Router
   • Infotainment System
   • Power Inverter / Motor Driver
5. Course Summary
   • Review of Key Concepts
   • Resources for EMC and Signal Integrity Engineers

Course Instructor

Dr. Todd H. Hubing is the Michelin Professor of Vehicle Electronics at Clemson University and Director of the Clemson Vehicular Electronics Laboratory. He and his students at Clemson have worked on the development and analysis of a wide variety of electronic products. EMC design rules can vary greatly depending on whether you are designing high-speed computing equipment, low-cost mixed-signal consumer products or high-power industrial controls; but the basic EMC principles are the same in all industries. By applying these principles in an organized manner, it is possible to review a design circuit-by-circuit to guarantee that any particular EMC requirement will be met. This approach is more effective than the blind application of design guidelines and is the primary emphasis of every EMC design class taught by Dr. Hubing.