AD/DA conversion

How many comparators does a 3-bit flash AD converter need?

  1. A8
  2. B7
  3. C3
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Answer: B. 7

A flash ADC compares the input with every threshold at once, so N bits require 2ᴺ − 1 comparators. For 3 bits that is 2³ − 1 = 7. Because the number of comparators grows exponentially with the number of bits, flash ADCs are not suited to high resolution.

  • A. 8 is the number of output levels; there is one fewer boundary between them.
  • B. Correct. 2³ − 1 = 7.
  • C. 3 matches the number of bits, the idea behind deciding one bit at a time as in successive approximation.
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More AD/DA conversion questions

  1. If a 10 kHz sine wave is sampled at 12 kHz without an anti-aliasing filter, at what frequency does it appear?
  2. Which correctly describes the SFDR (spurious-free dynamic range) of an AD converter?
  3. How many comparisons does an N-bit successive-approximation AD converter basically perform per conversion?
  4. Which correctly describes the acquisition time of a sample-and-hold circuit?
  5. What is the technique of deliberately sampling a signal centered at 70 MHz with a 10 MHz bandwidth at a lower sampling frequency, which also performs frequency conversion?