Precautions for Clock Placement on a PCB Board

• Layout Tips:

  When designing a PCB board for a clock circuit, consider the following:

  • Position the clock crystal centrally on the PCB over a solid ground plane.
  • Avoid placing other circuits near or underneath the crystal to prevent signal interference.
  • Implement shielding measures for the clock crystal and associated circuits.
  • Ensure a copper area is placed under the crystal for proper grounding.

• Benefits of a Ground Plane:

  Having a ground plane under the clock crystal helps manage RF radiation, aids in heat dissipation, and reduces common mode currents.

• Shared Clock Traces:

  Use a radial topology connection for clock signals and ensure proper routing according to characteristic impedance.

• Clock Transmission Line Requirements:

  Place a complete image plane layer adjacent to the clock routing layer, minimize routing length, and control impedance.

• Issues to Avoid:

  Avoid disruptions in the image PCB ground loop, surge voltages on the image plane, and crosstalk between different clock signals.

• Routing the Clock Signal:

  Route clock lines on inner layers as strip lines for better RF transmission path and lower impedance. Consider using microstrip lines on outer layers.