DAC monotonicity criterion: “A DAC is monotonic if its output strictly increases whenever its binary input code is incremented to the next higher value.” Assess this definition.

Introduction / Context:
Monotonicity is a critical DAC property for closed-loop control and instrumentation. A nonmonotonic DAC can reverse direction for some code step, causing control loops to become unstable or measurements to glitch. Understanding the formal definition distinguishes it from linearity metrics such as DNL and INL.

Given Data / Assumptions:

• Binary-weighted codes; assume ideal coding (e.g., straight binary).
• Increment by 1 LSB in digital code.
• Evaluate output change with each step.

Concept / Approach:
Monotonic means “never decreases when the input code increases.” A strictly increasing (or at least nondecreasing) analog output over the entire code range satisfies monotonicity. DNL (differential nonlinearity) less than 1 LSB guarantees monotonicity; if DNL exceeds 1 LSB, negative steps can occur, breaking monotonic behavior. The concise statement in the question aligns with the practical definition used in datasheets and control literature.

Step-by-Step Solution:

Verification / Alternative check:
Datasheets explicitly state “monotonic to N bits” and relate it to maximum DNL. Testing involves scanning codes and ensuring no downward transitions occur.

Why Other Options Are Wrong:

• Incorrect: Opposes standard terminology.
• Only true for current-steering: Architecture-independent property.
• Ambiguous; needs INL: INL does not define monotonicity; DNL does.

Common Pitfalls:
Confusing monotonicity with absolute accuracy; believing an INL of 0 is required (it is not).

Final Answer:
Correct