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Design of High-Speed Circuits 🚧

Factors to Consider in High-Speed PCB Design

  • Cost control
  • Layer stack-up principles
  • Layout principles
  • Routing principles
  • Impedance design
  • Signal integrity
  • Power integrity
  • EMC design
  • Thermal design
  • DFM design

Differences Between Two-Layer and Multilayer Boards

  • Calculation of reference planes and impedance
  • Shorter return paths in multilayer boards
  • Easier routing
  • Higher cost of multilayer boards

Layer Stack-up Guidelines

  • Components and soldering surfaces should have complete ground planes (for shielding purposes)
  • Avoid adjacent parallel routing layers as much as possible (to prevent interference)
  • All signal layers should be adjacent to ground planes; critical signals should be adjacent to ground layers without crossing split planes (to minimize return paths)

Based on the above, the recommended layer stack-up scheme is:

  • Top layer: Signal 1
  • Inner layer 1: Ground
  • Inner layer 2: Power
  • Bottom layer: Signal 2

To reduce edge radiation, the power layer should be pulled back at least 1 mm from the ground layer.

PCB Impedance Design Requirements for Different Communication Protocols

High-Speed Signal Impedance Requirement Tolerance Routing
DDR 100Ω ±10%
eMMC 50Ω ±10%
USB 90Ω ±10% Differential
HDMI 100Ω ±10%
eDP 90Ω ±10% Differential
MIPI 100Ω ±10% Differential

Some Basic Concepts

  • Signal Integrity: Signal integrity refers to the quality of a signal on a signal line. Good signal integrity means that the signal has the necessary voltage levels when needed.
  • Transmission Line: A transmission line is a connection line composed of two conductors

References and Acknowledgements

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