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HF-Protection of Electronic Circuits

Learn how to protect electronic circuits from external and internal noise sources with shielding techniques. This overview covers noise sources, basics of shielding, and provides examples and an outlook on future developments.

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HF-Protection of Electronic Circuits

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  1. HF-Protection ofElectronic Circuits Thomas Losert

  2. Overview • Noise Sources (External, Internal) • Basics about Shielding • Examples • Outlook

  3. Overview • Noise Sources (External, Internal) • Basics about Shielding • Examples • Outlook

  4. External Noise Sources • External noise is received mostly through I/O-connectors or electromagnetic waves • Shield I/O connectors (or even the cables) and/or use filters for blocking noise • Use a star-topology for ground, i.e. connect all ground lines in a common point

  5. Internal Noise Sources • Internal noise is caused mostly by signals with high frequency (e.g. Oscillator of Microcontroller) or high currents (e.g. switching power supply) • Minimize length of circuit paths that could act as antennas for noise signals (e.g., ground-planes) • Maximize Distance to sensitive signals (e.g. measurement signals) • Subdivide the system in (nested) „System Zones“ and use filters for blocking noise at the boundaries • Eliminate noise sources (e.g., no floating input pins)

  6. Overview • Noise Sources (External, Internal) • Basics about Shielding • Examples • Outlook

  7. Basics about Shielding • Due to the „skin effekt“ for higher frequencies a thinner shield is sufficient(e.g., conductive foil, tape, or paint) • For higher frequencies (shorter wavelengths) the tolerable gap dimension in the shield decreases • Noise should be eliminated at the source if possible (e.g., decoupling capacitors) • Noise sensitive circuits should be separated from noise sources (e.g., ground planes, conductive material, or distance)

  8. Overview • Noise Sources (External, Internal) • Basics about Shielding • Examples • Outlook

  9. Example: Decoupling Capacitors

  10. Example: Ground Planes • Current can only flow in loops • Larger loops (bigger „antennas“) emit more noise • Dedicated ground-planes help minimizing the effective area of the loop • Ground-planes should not be used for routing of other signals • Adding paths to the ground-plane require a detailed analysis of every track on the board (otherwise the ground-plane could be wasted)

  11. Example: Shielded Circuit • Metal case protects against undesired electro-magnetic waves • feed-through capacitor for decoupling the power supply

  12. Example: Subdivision of a System • Further shielding could be achieved with compartments of conductive material • For shielding of ventilation openings lattice-like panels are available

  13. Example: Path to Ground • Separate high noise/current lines and analog/sensitive signals

  14. Overview • Noise Sources (External, Internal) • Basics about Shielding • Examples • Outlook

  15. Outlook On Saturday, May 1st, 2004 same time, same place „PCB Design“

  16. Vielen Dank für Ihre Aufmerksamkeit ! Noch Fragen? Thomas.Losert@tuwien.ac.at

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