Distinguish between static and dynamic hazard. How will youdetermine hazard in combinational circuits?

Distinction between Static and Dynamic Hazard

1. Static Hazard:

   • A static hazard occurs in a digital circuit when the output is expected to remain constant but changes due to slight variations in propagation delays.
   • Types: There are two types of static hazards:
     • Static 0 hazard: Expected output is 0, but briefly changes to 1.
     • Static 1 hazard: Expected output is 1, but briefly changes to 0.
   • Example: If you have a logic circuit designed to output 0, a static 0 hazard might cause the output momentarily to go to 1 because of a delay in the arrival of signals.

2. Dynamic Hazard:

   • A dynamic hazard occurs when the output of the circuit changes more than once during the transition between states, despite the correct final output value.
   • Dynamic hazards involve more complex transitions where the output oscillates several times before settling on the correct final state.
   • Example: If a logic circuit is changing its state from 0 to 1, a dynamic hazard could cause the output to flicker between 0 and 1 several times before it finally stabilizes at 1.

Determining Hazards in Combinational Circuits

To determine hazards in combinational circuits, you can follow these steps:

1. Construct the Logic Equation:

   • Write down the complete logic equation based on the given circuit.

2. Create a Timing Diagram:

   • Sketch the timing diagram for the inputs and determine the expected output changes based on the logic equation.

3. Identify Critical Paths:

   • Analyze the critical paths in the circuit where timing differences may introduce hazards.

4. Simulate Transitions:

   • Use simulation to track the output during transitions of inputs. This can help visualize if the output oscillates or stabilizes correctly.

5. Check for Static Hazards:

   • Identify situations where an input change should not affect an output but does, indicating a static hazard.

6. Check for Dynamic Hazards:

   • Observe scenarios where the output changes multiple times during a single input transition.

By following these steps, you can analyze and identify potential hazards in your combinational circuits effectively.