Quantization levels vs. resolution: With 4-bit resolution, is it possible to obtain more than 16 distinct analog output levels from an ideal DAC?
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AIncorrect
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BCorrect
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CCorrect if oversampling is used
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DCorrect with noise shaping alone
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EDepends only on Vref value
Answer
Correct Answer: Incorrect
Explanation
Introduction / Context:Resolution defines how many discrete codes a converter can represent. An ideal n-bit DAC has 2^n unique digital codes and therefore 2^n analog output steps. This question probes whether learners equate “4-bit resolution” with a precise, finite set of quantization levels and resist the temptation to assume extra levels can be created without changing resolution.
Given Data / Assumptions:
- Ideal, memoryless 4-bit DAC (no dynamic tricks).
- Uniform code mapping across its defined output span.
- No dithering, averaging, or time-domain modulation considered in the static sense.
Concept / Approach:For an ideal DAC, the number of distinct output levels equals the number of input codes: 2^n. With n = 4, that is 16 levels. Each step is one least significant bit (LSB) in amplitude. Although advanced techniques such as oversampling with noise shaping, pulse-width modulation, or time-averaging can effectively increase apparent resolution over time, the instantaneous static output still presents one of the 16 levels at any sample instant for a pure 4-bit DAC core.
Step-by-Step Solution:
Compute levels: 2^n → 2^4 = 16.Interpret properly: “More than 16” contradicts the definition of 4-bit resolution.Conclude: The statement is not valid for an ideal static DAC.Verification / Alternative check:Look at a 4-bit transfer characteristic: a staircase with 16 steps from code 0000 to 1111. No intermediate static plateaus exist without extra modulation or analog filtering of a higher-rate bitstream.
Why Other Options Are Wrong:
Correct / oversampling / noise shaping: These refer to techniques that improve effective resolution over time, not the core static number of levels.Depends on Vref: Vref sets absolute amplitudes, not the count of distinct levels.Common Pitfalls:Confusing effective number of bits (ENOB) improvements from dynamic methods with the inherent code count of the DAC.
Final Answer:Incorrect