AGENDA - EMC SYSTEMS ENGINEERING DESIGN SEMINAR
EMC problems have plagued the communications/electronics industry since the late 1800's. This is significant because these early problems preceded Lee Deforestís invention of the triode vacuum tube. When the amplification of low level signals became possible, the EMC problem became much worse because circuits could now respond to lower level interfering signals. Fortunately, there were few electronics devices to interfere, and in general they were analog! In the last 100 years, we have seen a proliferation of modulation schemes, active components, devices, and systems. Electronics is now generally digital, and generates considerable RF interference. This has resulted in the creation of laws by various governmental agencies to protect our RF environment. To cost effectively comply with these laws requires a coordinated design effort between the electronics designers, and the mechanical/packaging designers.
This seminar provides an overview of the EMC problem, an examination of logic EMC characteristics, and EMC systems design. The systems design presentation covers printed circuit board considerations, differential and common mode trace and cable EMC hardening, and shielding for RF emission and susceptibility (immunity) control. The emphasis will be on radiated emission from chips, interconnects, and cables; radiated susceptibility of circuits; as well as the design principles used to resolve EMC problems. The shielding discussion covers aperture controls as well as mechanical and corrosion design. Shielding design is covered in this presentation because it can be applied to existing systems without impacting signal integrity/circuit operation. It is the only suppression technique that can be used in this way.
1. OVERVIEW OF EMI/RFI/EMC PROBLEM
Examples of Interference Conditions Interference Sources Interference Receptors F.A.S.T. Analysis Systems Emission/Immunity
2. EUROPEAN EMC DIRECTIVE
Note: An overview of MIL-STD-461 can be substituted
CE Conformance Mark Council Directive 89/336/EEC Article 4 EC Commercial Requirements Routes to Compliance Declaration of Conformity Costs to meet EMC requirements
3. SYSTEMS DESIGN
Conducted vs Radiated Emission Simplified Circuit Loop Radiation Equation Maximum Loop Area to meet emission limits Simplified Circuit Loop Pickup Equation Design Emphasis Spectrum Density vs Pulse Shape High Speed Devices
4. PCB/CABLE DESIGN PRACTICES
PCB Radiation loops Partitioning by speed/frequency PCB Layout & Design Considerations Multilayer PCB's Wire, Grid, Plane Impedance Ungrounded Conducting Surfaces DM/CM Trace & Cable Noise Reduction Ferrite Bead Attenuation
5. PCB/EQUIPMENT SHIELDING
Containment/Exclusion Shielding characteristics Graphical representation Absorption and Reflection equations Shielding Effectiveness vs Frequency PCB/Equipment shielding compromises Aperture Integrity Window and vent panels
6. RF GASKETS
Seam design and three most popular configurations High performance enclosures seams Future Bus card cage Mechanical/Electrical Considerations Qualitative Shielding Effectiveness Electro-Galvanic Compatibility