Question

The number of comparators required for implementing an 8-bit flash analog-to-digital converter is
1. 8
2. 128
3. 255
4. 256

Answer 1

Correct Answer - Option 3 : 255

Flash Type ADC:

• Flash type Analog to Digital converter (ADC) converts the analog signal to digital signal.
• It is the fastest ADC Converter as compare to other ADC.
• A number of comparators used for N-bit Flash type ADC are (2N -1) and, so for 4 bit Flash type ADC will require 15 no. of the comparator.
• Flash type ADC requires (2N × N) priority encoder and 2N no. of the resistor, so for 4-bit flash type ADC requires 16 × 4 priority encoders and 16 resistors.
• Resolution of Flash type ADC is V/(2N) so for 4 bit Flash type ADC  have resolution V/16.
• So if there is a change in input voltage by V/16 it will change the LSB of the output.

 

Calculations:

Number of comparators required for implementing an n-bit flash ADC.

are, N = 2ⁿ – 1

Given that, n = 8

N = 2⁸ – 1 = 255