Dynamic Hazard in asynchrnous circuit

[Urvashi]

In asynchronous ckt, which of the foll. best explain a dynamic hazard
a)o/p changes several times for a single change in i/p
b)o/p changes to a different state for a single change in i/p
c)o/p changes momentarily when it is supposed to remain constant for a single change in i/p
D)none

 

[sudarmathi]

i guess option a best explains the cause of dynamic hazard in asynchronous circuit. the result of this may lead to unexpected output state since the wrong state could be latched up before output is settled to correct final state.

 

[Urvashi]

i am not getting your point, please clearly describe. And suggest me which option is right of 4.

 

[sudarmathi]

option a is the cause(multiple o/p change for single input change) and option b is the effect(where asynchronous circuit goes to different state than expected). option a is more appropriate.
For example, consider above image as hazardous output signal. when signal changes between 0 to 1 it takes multiple transitions and settles after time t.if the signal is latched after this transition time t, no isssue. but if o/p is latched before time t, 0 will be latched instead of 1. so it may reach different state.

 

[Urvashi]

thank you!!

 

[iVenky]

Here's what I have taken from wikipedia-"

"Hazards are a temporary problem, as the logic circuit will eventually settle to the desired function. However, despite the logic arriving at the correct output, it is imperative that hazards be eliminated as they can have an effect on other connected systems."

So this clearly means that (b) option is wrong.

"A static hazard is the situation where, when one input variable changes, the output changes momentarily before stabilizing to the correct value.
A dynamic hazard is the possibility of an output changing more than once as a result of a single input change. Dynamic hazards often occur in larger logic circuits where there are different routes to the output (from the input). If each route has a different delay, then it quickly becomes clear that there is the potential for changing output values that differ from the required / expected output. e.g. A logic circuit is meant to change output state from 1 to 0, but instead changes from 1 to 0 then 1 and finally rests at the correct value 0. This is a dynamic hazard."

So clearly the answer is (a).