Stuck-at Faults

"Stuck-at faults" are a type of fault model used in digital circuit testing to simulate common types of defects that can occur in hardware.

What are Stuck-At Faults?

A stuck-at fault assumes that a signal line (such as a wire or a gate output) is "stuck" at a constant logic level, regardless of the actual input or expected behavior.

There are Two Types :

Stuck-at-0 (SA0): The node is stuck at logic 0.

Stuck-at-1 (SA1): The node is stuck at logic 1.

Why use stuck-at fault models?

They are a simplified and effective model for:

• Testing digital circuits (to ensure manufacturing defects don't break the logic).

• Fault simulation and automatic test pattern generation (ATPG).

Example

Imagine this logic:

Normally, Z = A AND B.

If input A is stuck-at-0 (SA0), then:

• No matter the value of B, Z will always be 0.

• This is a fault, and testing should catch it.

In Testing

• Stuck-at fault testing helps in detecting defects like:

  • Broken wires

  • Transistor failures

  • Short circuits

• It's the most commonly used model in combinational and sequential logic testing.