Question

Sample and hold circuits in A/D converters are designed to

• A. \( \text{Stabilize the comparator's threshold voltage during the conversion process} \)
• B. \( \text{Sample and hold the output of the binary counter during the conversion process} \)
• C. \( \text{Sample and hold the D/A converter staircase waveform during the conversion process} \)
• D. \( \text{Stabilize the input analog signal during the conversion process} \)

Hint:

The main purpose of a Sample and Hold circuit in an ADC is to mitigate the effects of changing input signals during the finite conversion time. It effectively takes a "snapshot" of the analog voltage at a specific instant and holds that value constant, ensuring accurate analog-to-digital conversion even for rapidly varying input signals. This is critical for preventing "aperture error" or "aperture uncertainty."

Answer 1

The Correct Option is D

To solve this problem, we need to understand the role of sample and hold circuits in Analog-to-Digital (A/D) converters.

1. Understanding Sample and Hold Circuits:

– A sample and hold circuit is used in A/D converters to capture (sample) the input analog signal at a specific moment in time and hold that value steady for the duration of the conversion process. This ensures that the A/D converter operates on a stable input signal during the conversion process, rather than a changing signal.

– The main purpose of the sample and hold circuit is to stabilize the input analog signal so that the conversion process can proceed accurately without being affected by fluctuations or noise in the signal.

2. Analyzing the Options:

- Option 1: "Stabilize the comparator's threshold voltage during the conversion process" – This is not the primary function of the sample and hold circuit. The sample and hold circuit does not directly stabilize the comparator's threshold but rather stabilizes the input signal. 
- Option 2: "Sample and hold the output of the binary counter during the conversion process" – This is incorrect. The sample and hold circuit deals with the input signal, not the output of the binary counter. 
- Option 3: "Sample and hold the D/A converter staircase waveform during the conversion process" – This is incorrect because the sample and hold circuit operates on the input analog signal before it reaches the A/D converter, not the output of the D/A converter. 
- Option 4: "Stabilize the input analog signal during the conversion process" – This is correct. 
The sample and hold circuit ensures that the input analog signal is held steady during the conversion process, preventing errors caused by signal variations.

Final Answer:

The correct answer is "Stabilize the input analog signal during the conversion process".