Monotonicity definition: A DAC is called nonmonotonic if its output magnitude increases for every increasing input code. Classify this statement.

Difficulty: Easy

Correct Answer: Incorrect

Explanation:


Introduction / Context:
Monotonicity is critical in control and instrumentation: as the input code steps up, the analog output should never step down. Misstating the definition leads to misinterpretation of datasheets and system stability issues.


Given Data / Assumptions:

  • Monotonic DAC: output does not decrease when input code increases by one step.
  • Nonmonotonic DAC: at some code transition, output decreases (step reversal).
  • Architecture (R-2R, current steering, segmented) does not change the definition.


Concept / Approach:
The statement provided actually defines monotonic behavior, not nonmonotonic. A nonmonotonic DAC can create control loop oscillations or dead zones because increased command produces a lower output near certain transitions—an unacceptable condition for many applications.


Step-by-Step Solution:

Recall correct definition of monotonicity: nondecreasing output for increasing input code.Identify contradiction: the claim equates that behavior with “nonmonotonic.”Conclude classification: the statement is incorrect.Note: Nonmonotonicity is often linked to DNL errors > 1 LSB.


Verification / Alternative check:
Check DNL: if worst-case DNL ≤ 1 LSB, the DAC is guaranteed monotonic. If DNL exceeds 1 LSB, nonmonotonic steps can occur, confirming the industry usage of the term.


Why Other Options Are Wrong:

Correct/architecture qualifiers: Monotonicity definitions are universal, independent of coding scheme or architecture.


Common Pitfalls:
Confusing monotonicity with linearity; assuming glitch energy implies nonmonotonicity (glitches are transient, not static step order errors).


Final Answer:
Incorrect

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