The GATE Grind

GATE 2021 IN – Question 20

Digital Electronics · ADC and DAC · 1 mark · Multiple select

For a 4-bit flash ADC with full-scale input range $V$, which statements are true?

  1. It requires 15 comparators
  2. It requires one 4-to-2 priority encoder and 4 comparators
  3. An input change $V/16$ will always flip the output MSB
  4. An input change $V/16$ will always flip the output LSB

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Show answer and explanation

Correct answer: (A) It requires 15 comparators; (D) An input change $V/16$ will always flip the output LSB

Explanation

There are 2⁴=16 codes and 15 transition thresholds, so 15 comparators are needed: A. Within the unsaturated conversion range, increasing input by one code width V/16 advances the code by one and toggles its LSB: D. It does not always toggle the MSB, and four comparators with a 4-to-2 encoder are insufficient. **A,D**.