Grouping Components

Different Susceptible Systems

Low Speed Digital

  • Not very susceptible to noise
  • Generates a medium amount of noise, so keep it away from the most noise sensitive circuits
  • The most active signals are the most noisy
  • Other than that, layout is not too critical and this can be placed around the board as kind of a “filler” in places where nothing else will want to go and can be easily auto-routed.

High Speed Digital

  • Same as low speed digital, plus the following:
  • There can be a very high number of interconnecting traces
  • Generally uses controlled impedance traces
  • Requires controlled, minimized, or matched signal delay times and proper location of termination devices
  • Can generate some serious heat - added copper planes to conduct heat away and heat sinks will need to be designed in

Analog

  • Usually very sensitive to noise pickup
  • Keep away from noise generators
  • High impedance nodes and nodes followed by a lot of gain are generally most sensitive to noise
  • Look for recommended grounding and shielding in application notes
  • May also be sensitive to surface leakage currents, temperature, etc
  • Power amplifiers may generate significant heat - added copper planes to conduct heat away and heat sinks will need to be designed in

Power

  • Can generate a lot of noise (esp. switching power supplies, class D amplifiers, etc)
  • At the same time, some nets are very sensitive to noise (i.e. sense and feedback nets)
  • Can generate a lot of heat - added copper planes to conduct heat away and heat sinks will need to be designed in
  • Switching nodes are sensitive to layout parasitic inductance and capacitance
  • Keep high AC currents confined to small loop areas to reduce noise
  • May involve high voltage and safety issues, special spacing and insulation requirements

RF

  • Uses controlled impedance traces
  • May require traces to be designed as antennas (requires RF design background)
  • Receivers are very sensitive to noise
  • Transmitters generate noise and dissipate heat proportional to the power involved
  • Again, added copper planes to conduct heat away and heat sinks will need to be designed in
  • Requires special attention to shielding and grounding