EMI/EMC Troubleshooting: Principles and Demonstrations

Summary

This three day course covers the fundamentals for troubleshooting an electronic design with electromagnetic interferences (EMI), or Electromagnetic Compatibility (EMC) problems. Troubleshooting or debugging EMI problems is usually frustrating especially when a trial and error strategy is used. Discover how to localize, characterize, and solve emissions and immunity EMI problems in a very understandable and entertained style.

The course presents how an electronic system can generate and/or receive EMI resulting in a failure to meet EMC regulations. A practical approach with many real world examples, techniques, simulations and hardware tools for EMI/EMC troubleshooting will be explained with an emphasis to minimize costs, production and marketing delays by considering key factors and techniques in the design phase or to evaluate solutions for the production stage.

No prior EMI/SI knowledge is needed but an electrical engineering background (BSEE or equivalent experience) is recommended.

The course includes real examples and demonstrations of problems with reference to narrowband and broadband signals in digital and analog circuits, audio problems, power supplies, etc.

Learning objectives

Upon completing the course you will be able to:

• understand the basics and fundamentals of EMI and EMC issues
• analyze a system with problems looking for culprit-coupling mechanism and victims
• use EMI diagnostic and troubleshooting techniques to locate and fix EMI/EMC problems in equipment already finished
• locate and fix EMI/SI/EMC problems in a product or installation
• know the way of doing simple prequalification EMC tests
• reduce time and cost of EMI/SI diagnostic and fixes

Target Audience

• Design engineers/technicians from the electronics industry involved in EMI/EMC problems
• Those interested in a working knowledge of EMI/EMC engineering principles and concerned with EMI/EMC problems as circuit designers, PCB layout engineers, or mechanical designers
• Laboratory personnel involved in measurement and troubleshooting of EMC failures
• Managers responsible for design, production, test and marketing of electronic products

Outline

BASICS OF EMI/EMC: KEY FACTORS TO UNDERSTAND THE PROBLEM.

 • Electrical signals. Maxwell vs. Kirchhoff: limits of circuit theory. Spectrum of a signal: time domain vs. frequency domain. Resonance and Quality factor (Q) • Frequency vs. dimensions (size). Time vs. distance. Broadband and narrowband signals • EMI/EMC problems and philosophy. EMI/EMC classification (1): radiated vs. conducted. EMI/EMC classification (2): emissions vs. immunity • Culprits and Victims. Coupling mechanisms. Why EMI affects electronic systems, examples. EMI/EMC tests basics: emissions and immunity/susceptibility • High frequency effects: skin effect, return current and parasitics. The importance of rise time and fall times (dv/dt and di/dt). Key factors for EMI • Controlling signal return currents. Differential vs. common mode currents. Non ideal components. The “hidden schematic” concept •  Antenna basics: dipoles and loops. Antenna resonance. Near vs. far field. Low and high impedance signals and circuits. “Hidden antennas”: radiation and pickup

ANALYSIS OF THE PROBLEM. YOUR DESIGN IS FAILING, NOW WHAT ?

 • Keep calm, how to think: the strategy. Failing in design/development versus failing in production/installation • Typical limitations: cost, time, and space. Additional problems: stress and pressure. Learning from experience: similar failures in the past. Looking for useful information. Key parameters

INSTRUMENTATION FOR TROUBLESHOOTING. TRYING TO SEE THE PROBLEM.

 • Time domain (scope) vs frequency domain (spectrum analyzer). Tracking generator. VSWR bridge. Impedance analyzer. • A new and powerful tool: scope with advanced FFT for time and frequency domain analysis.

TOOLS FOR TROUBLESHOOTING

 • Voltage probes · Current probes · Amplifiers for emissions · Antennas · Amplifiers for immunity · Small TEM cells · Near-field probes (E&H) • Near-field scanners · ESD and transient generators · ESD detectors · Special probes both homebrew and commercial

A REVIEW OF TYPICAL FAILURES IN ELECTRONIC SYSTEMS

Ground system

 • Signal ground vs. safety ground. Ground impedance is too high. Big return paths. Common impedance. Ground loops.

Filters

 •  Source and load influence: terminal impedances and filter topology. Reflection vs. dissipation. Parasitic in components. Ferrites and inductor saturation and undesired coupling effects. • Resonances and ringing. Defective filter location, mounting and layout.

PCB layout

 • Partitioning and critical zones. Number of layers and distribution. Power planes design and distribution: power integrity (PI). • Layout problems: long paths, uncontrolled impedance, signal integrity (SI), corners, vias. Slots and discontinuities in ground planes. • Defective decoupling and bypass networks (how, where, resonances, etc.). Crosstalk. Mixed signal PCBs (A/D designs). •  Controlling clock waveform. Clock distribution. Parasitics oscillators versus underdamped systems.

Shields

 • Low vs. high frequency fields, electric vs. magnetic fields. Reflection vs. absorption. • Why the shield can be destroyed. How to destroy a shield: holes and slots, shield penetrations, holes for fans and displays. • Shields and paint (for good and bad results). Transformer stray fields.

Cables

 • Cables as antennas for emissions and pickups. Big return paths. Uncontrolled impedance: transmission line effects. • Inadequate cable for your application: wires, twisted pairs, coax, shielded cables, and ribbon cables. • Defective shields: material, coverage, and pigtails. Crosstalk. Common impedance in cables.

TROUBLESHOOTING TECHNIQUES

 • Measuring high frequency voltages. Measuring high frequency currents: differential vs common mode. Scope and probe limitations • Finding resonances in components, circuits, PCBs, cables and enclosures. Finding sources · Finding victims. • Repeatability · Review of some typical errors in measurement techniques. Detecting ESD events · Injecting noise in circuits · Your finger · Apply heat or cold!.

SPECIAL COMPONENTS FOR TROUBLESHOOTING

 • Two terminal capacitors · Ferrites · Three terminal and feed through components • Filters · Shields for high/low frequencies • Shielding tape · Gaskets · Resistors · Other useful accessories.

TROUBLESHOOTING EXAMPLES

 • Real world examples analyzed and solved using some of the previous techniques and components including narrowband and broadband signals in digital and analog circuits, audio, power supplies (SMPS), power electronics, etc.

PRACTICAL DEMONSTRATIONS