Hazards/glitches

• Hazards/glitches: Undesired switching at the circuit output

  • Occur when different pathways through a circuit have different propagation delays
  • Dangerous if logic makes a decision while output is unstable

• Types of hazards

  • Static (static-0 and static-1)
  • Dynamic

• Solutions

  • Wait until signals are stable (use a clock — synchronous design)
  • Design hazard-free circuits
    • Sometimes asynchronous design is unavoidable
    • Hazard-free design is difficult when logic is multilevel

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