Understanding the flash (parallel) ADC principle The flash method of analog-to-digital conversion uses an array of comparators that compare reference voltages with the analog input voltage to generate a thermometer code.
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ACorrect
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BIncorrect
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CApplies only to sigma-delta converters
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DValid only for 1-bit quantizers
Answer
Correct Answer: Correct
Explanation
Introduction / Context: Flash (parallel) ADCs are renowned for extremely high conversion speeds. They achieve this by using many comparators operating in parallel to compare the input against a ladder of reference voltages, producing a thermometer code that is then encoded into binary.
Given Data / Assumptions:
- An N-bit flash ADC employs 2^N - 1 comparators.
- A resistor ladder generates evenly spaced reference levels.
- Digital encoding logic converts the thermometer pattern to binary output.
Concept / Approach: Each comparator outputs 1 if Vin exceeds its reference and 0 otherwise. The boundary where outputs switch indicates the quantization level. Because all comparisons happen simultaneously, latency is only the comparator and encoder delay, making flash the fastest ADC architecture.
Step-by-Step Solution:
Build a reference ladder producing Vref*(k/2^N), for k = 1..2^N-1.Compare Vin to each reference using parallel comparators.Capture the thermometer code where ones transition to zeros.Encode this pattern into the N-bit digital output.Verification / Alternative check: Sweep Vin from 0 to Vref and verify monotonic step transitions at expected thresholds; check DNL/INL using measured transition points.
Why Other Options Are Wrong: “Incorrect” contradicts the flash architecture. The other options refer to unrelated converter types or bit depths.
Common Pitfalls: High power and large area due to many comparators; input kickback; encoder bubble errors requiring bubble-correction logic.
Final Answer: Correct