Step size of a 6-bit ADC over a 0–7 V input range An analog signal varies from 0 V to 7 V and is digitized by a 6-bit ADC. What analog value does each 1-LSB step represent on the digital output?
Digital Electronics
Interfacing to the Analog World
Difficulty: Easy
Choose an option
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A0.111 V
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B1.17 V
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C0.109 V
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D0.857 V
Answer
Correct Answer: 0.109 V
Explanation
Introduction / Context:Knowing the LSB size of an ADC allows quick estimation of quantization error and measurement resolution across a given input range.
Given Data / Assumptions:
- Input span: 0 to 7 V.
- Resolution: 6 bits → 64 codes.
- Ideal mid-tread behavior assumed for step size calculation.
Concept / Approach:The LSB step size for an ideal ADC is Step = Full-Scale Range / 2^N. Here, N = 6, so 2^N = 64.
Step-by-Step Solution:
Compute step: 7 V / 64 = 0.109375 V.Round to three decimals: ≈ 0.109 V.Therefore, each increment in the digital code corresponds to about 0.109 V of the input.Verification / Alternative check:2^6 = 64; 0.1 V × 64 = 6.4 V, so the precise 0.109375 V step is consistent with a 7 V span.
Why Other Options Are Wrong:
- 0.111 V: Close but not exact; it overestimates the step.
- 1.17 V / 0.857 V: These are far too large; they would imply minimal resolution (3–8 steps total).
Common Pitfalls:
- Dividing by 2^N − 1 for step size; while code count is 0..63, the step size calculation uses 2^N in ideal mid-tread models.
Final Answer:0.109 V