Which statement best describes a guideline for selecting an ADC reference voltage?

• A. The reference should be derived from the ADC supply rail
• B. The reference should be designed to minimize current draw
• C. The reference should be tailored to sensor impedance only
• D. Low noise, temperature-stable, and adequately accurate, matched to input range

Answer: (D)

The value used as the ADC reference sets the full-scale input and the size of each LSB, so its quality directly limits measurement accuracy and noise. The best guideline is to choose a reference that is low in noise, temperature-stable, adequately accurate, and matched so the sensor signal fits well within the ADC’s input range. A reference tied to the supply rail tends to inject noise and ripple into measurements, degrading precision. Prioritizing only minimizing current draw can compromise stability and accuracy. Focusing solely on sensor impedance ignores how reference noise and drift affect the conversion results. With a clean, stable reference that remains within spec across temperatures and ages, the ADC can deliver consistent readings and fully utilize its resolution. If needed, buffer the reference to prevent loading and ensure the reference pin sees an appropriate source impedance.