Question

Minimum number of comparators required to implement 6-bit flash ADC

• A. 63
• B. 31
• C. 127
• D. 65

Hint:

Flash ADCs require \( 2^N - 1 \) comparators and \( 2^N \) resistors.
If the question asked for resistors instead of comparators, the answer would have been \( 2^6 = 64 \).
Keep this distinction in mind for competitive exams.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the minimum number of voltage comparators required to construct a 6-bit Flash Analog-to-Digital Converter (ADC).

Step 2: Key Formula or Approach:
For an \( N \)-bit Flash ADC, the number of comparators required is:
\[ \text{Number of Comparators} = 2^N - 1 \]

Step 3: Detailed Explanation:

• A Flash ADC (also known as a parallel ADC) is the fastest type of ADC. It uses a series of resistors to divide a reference voltage into \( 2^N \) equal voltage steps.

• A comparator is connected at each voltage node (excluding the ground node) to compare the analog input voltage against the reference step.

• This simultaneous comparison requires exactly \( 2^N - 1 \) comparators for a resolution of \( N \) bits.

• Given the number of bits, \( N = 6 \):
Calculate the number of comparators:
\[ \text{Comparators} = 2^6 - 1 = 64 - 1 = 63 \]
• This large number of comparators (63) is the reason why Flash ADCs are highly complex, power-hungry, and typically limited to lower resolutions (usually $\le$ 8 bits) despite their high speed.