ADC accuracy – identifying common causes of conversion errors Which of the following can directly cause inaccurate analog-to-digital conversion results in practical systems?

Introduction / Context:
Accurate ADC measurements require a stable input during conversion and proper front-end behavior. Many architectures depend on a sample-and-hold (S/H) to freeze the input so the converter sees a constant voltage while it works.

Given Data / Assumptions:

• An ADC and its front-end are being evaluated for accuracy issues.
• We consider typical error sources in mixed-signal systems.

Concept / Approach:
A faulty or underperforming sample-and-hold causes droop, aperture uncertainty, or feedthrough during conversion, introducing conversion errors, especially with fast or noisy signals. By contrast, a stable constant input is ideal; a generic “linear ramp” is not inherently inaccurate; and intermittent counter inputs usually refer to digital control problems rather than intrinsic conversion inaccuracy unless they affect timing catastrophically (a separate fault domain).

Step-by-Step Solution:

Verification / Alternative check:
Datasheets specify S/H acquisition time, droop rate, and aperture jitter. Violations of these specs or a failed S/H manifest as inconsistent or biased codes.

Why Other Options Are Wrong:

• Constant analog input voltage: Beneficial for accuracy; not a cause of error.
• Linear ramp usage: Common in testing; not inherently inaccurate.
• Intermittent counter inputs: A digital control issue; may stop conversions but is not the primary analog accuracy limiter compared to S/H failure.

Common Pitfalls:

• Blaming the ADC core while ignoring front-end hold conditions, source impedance, and reference stability.

Final Answer:
faulty sample-and-hold circuitry