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