Analog to digital convertor

Ron H

Joined Apr 14, 2005
7,014
An LM393 dual comparator would work for two bits.
An LM339 quad comparator would work for three or four bits.
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?
 

Papabravo

Joined Feb 24, 2006
13,529
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?
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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