Difference between Static-1 and Static-0 hazard

In this article, we will discuss the differences between Static-1 and Static-0 hazards. A hazard in a digital circuit causes a temporary fluctuation in the circuit output. In other words, a hazard in a digital circuit is a temporary disturbance in the ideal circuit operation. If we provide it some time, it will resolve itself. These disturbances or fluctuations occur when different paths from the input to output have different delays. Due to this, modifications to the input variables do not immediately affect the output but appear at the output after a small delay caused by the circuit building elements, i.e., logic gates.

What are Static hazard?

Static hazards (also referred to as static logic or static competition hazards) are one of the logic hazard types that can be encountered in the circuits of digital logic. This type of problem occurs because of the finite delay in signals that pass through gates, which later on form glitches, malfunctions, or spikes before they reach the stable signal. The main difference between Static-1 and Static-0 hazards is the setting that causes the condition resemblance and the behavior of the circuit.

Static-1 Hazard:

Static-1 hazard is the name given to the case when the output glitches briefly back to a 1 value prior to settling at its final correct 0 value, resulting from a transition from 1 to 0 in the input of either a logic gate or a combination of gates.

It happens when each of the paths through the logic gates is not well-matched for the propagation delays. For instance, we take an AND gate composed of two inputs, A and B. If input A changes from 1 to 0 while input B is still 1, the output of the AND gate should positively respond and change from 1 to 0 in an instant. Consequently, the displacements at the boundaries may shortly go back to 1 before eventually stabilizing at 0.

The conditions for a Static-1 hazard to occur are:

  • The logical gate result or a circuit's initial operation ought to be 1.
  • At this moment, there should be at least one input, which is 1, which changes to 0, resulting in the output going from 1 to 0.
  • Step responses for systems with different delays on the paths within the circuit do not match perfectly. Hence, the glitch jumped back to 1 for a while before settling to 0.

Static-0 Hazard:

Another hazard is a Static-0 hazard, which refers to the state of an input of a logic gate or a group of gates after a transition from 0 to 1, in which the output temporarily acts like it is a 0 before eventually settling to the correct 1 value.

It occurs when the propagation delay of some input nodes is smaller than the larger propagation of the other input nodes. As a result, the output goes to 0 for a brief moment before reaching the 1 state. For instance, the change of an input from 0 to 1 in an OR gate (A, B), having two inputs, should lead to the immediate change of the output from 1 to 0.

Nevertheless, because there are varying latencies, the output could first go back to 0 and then make the final jump to 1.

The conditions for a Static-0 hazard to occur are:

  • We will start with the gate output and the logic circuit being zero in the beginning.
  • For at least one of I/O to vary, the output should change from 0 to 1.
  • The speed along the circuit paths may be different, and therefore, a glitch will occur at the output, which will sit at 0 before it changes to 1.

Key differences between Static-1 and Static-0 Hazards:

Difference between Static-1 and Static-0 hazard

There are several differences between the static-1 and static-0 hazards. Some main differences between these hazards are as follows:

FeaturesStatic-1 hazardStatic-0 hazard
Definition:It is a short-term breakage in the output signal due to the adjustment of the input signal.It is an undesired momentary glitch on the output signal resulting from a change in the input signal.
Occurrence:Transitioning from 0 to 1 and back to 0 again can also cause serious health concerns.During the process of changing from 1 to 0 or from 0 to 1, fluctuation always occurs.
Cause:This problem occurs when members of an intercultural group follow different or incompatible paths of communication.The imbalance among the path construction schedules.
Timing:The data transition between two stable logic levels takes place at the midpoint of the clock edge.It occurs at the halfway point between the two stable logical levels of logic.
Effect on Output:Time-dependent changes in the output that end up with the long-term ones that contribute to the accuracy of the result.A temporary variation in the output value before getting settled into the correct one.
Hazard Detection:Logic circuit is analyzed to identify anomaly.The circuits are checked through digital testing.
Example:For a 2-input OR gate with a Static-1 hazard, it is possible that one input changes from 1 to 0 more quickly than the other input.Here, in Static-0 hazard, which occurs in a 2-input AND gate, the fast change from 0 to 1 from one input is faster than that of the other input.

Conclusion:

In conclusion, Static-1 and Static-0 hazards are non-recurring events in digital circuits that occur due to incorrect timings during signal transmission. Static-1 hazards usually deal with brief glitches caused by the output line being temporarily back to 1 before switching to 0 during the transition of 1 to 0 in the input. On the other hand, the Static-0 hazards are the condition where the output acts like a 0 transiently before it settles in 1, due to changeover from 0 to 1. They implement delay elements and input buffering to reduce or even eliminate risks to ensure the proper operation of a circuit. The mechanisms of hazard removal are often the key to the safe and sound of digital systems.






Latest Courses