Offset error in DAC transfer characteristics Which description best matches offset error for a digital-to-analog converter (DAC)?

Introduction / Context:
Static DAC errors are commonly categorized as offset error, gain (full-scale) error, differential nonlinearity (DNL), and integral nonlinearity (INL). Correctly identifying these helps diagnose performance issues and interpret data sheets.

Given Data / Assumptions:

• Zero-code and first-transition behavior indicate offset.
• Overall slope indicates gain error.
• Step uniformity indicates DNL; cumulative deviation indicates INL.

Concept / Approach:
Offset error shifts the entire transfer function by a constant amount. Practically, the first code transition occurs at a non-ideal level (too low or too high). In staircase terms, the whole staircase is displaced up or down without changing its slope.

Step-by-Step Solution:
Consider the ideal first transition at one-half LSB (for a mid-tread DAC) or at 0 V (for specific coding).If the measured first transition occurs earlier or later, a constant offset exists.This matches the description that “more or less input voltage is required for the first step than specified,” i.e., the step threshold is shifted.Therefore option (c) describes offset error most directly.

Verification / Alternative check:
Graphically, offset error is the vertical intercept difference between actual and ideal straight lines; once compensated, subsequent steps align (ignoring other errors).

Why Other Options Are Wrong:

• missing codes: A DNL issue where certain codes never appear.
• error in the slope: That is gain (full-scale) error, not offset.
• —: Not a technical description.

Common Pitfalls:

• Confusing offset with gain; offset shifts all codes equally, gain tilts the line.
• Assuming offset affects linearity; it does not, by definition.

Final Answer:
more or less input voltage is required for the first step than what is specified