Analog to digital convertor

Discussion in 'General Electronics Chat' started by Amjad, Dec 14, 2006.

  1. Amjad

    Thread Starter New Member

    Dec 14, 2006
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    I want to built a 2 or 3 bit ADC.
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    An LM393 dual comparator would work for two bits.
    An LM339 quad comparator would work for three or four bits.
     
  3. sci-3d

    Well-Known Member

    Aug 22, 2006
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  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    A flash A/D requires (2^n - 1) comparators, where n is the number of bits. For 2 bits, 3 comparators are required, because 4 states have to be discerned. For 3 bits, you need 7 comparators, etc.
    Is there a way to use fewer comparators without including a D/A?
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    Right. My idea was to pick thresholds in such a way that not all codes are valid. I did not elaborate very well and my math was certainly off the mark.

    So 4 comparators can distinguish 5 states and log2(5) is just a bit bigger than two. With 8 comparators you get 9 states for which log2(9) is just over three.
     
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