Monday, 29 October 2012

Half Subtractor and Full Subtractor

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Subtractor : Subtractor is the one which used to subtract two binary number(digit) and provides Difference and Borrow as a output.In digital electronics we have two types of subtractor.

  1. Half Subtractor
  2. Full Subtractor
Half Subtractor :Half Subtractor is used for subtracting one single bit binary digit from another single bit binary digit.The truth table of Half Subtractor is shown below.


 Like Adders Here also we need to calculate the equation of  Difference and Borrow for more details please read What is meant by Arithmetic Circuits?

Difference = A'B+AB'=AB
Borrow=A'B

The logic Diagram of Half Subtractor is shown below.



Full Subtractor : A logic Circuit Which is used for Subtracting Three Single bit Binary digit is known as Full Subtractor.The Truth Table of Full Subtractor is Shown Below.


 From the Truth Table The Difference and Borrow will written as

Difference=A'B'C+A'BB'+AB'C'+ABC
Reduce it like adder
Then We got
Difference=ABC
Borrow=A'B'C+A'BC'+A'BC+ABC
=A'B'C+A'BC'+A'BC+A'BC+A'BC+ABC    ---------->  A'BC=A'BC+A'BC+A'BC
=A'C(B'+B)+A'B(C'+C)+BC(A'+A)
Borrow=A'C+A'B+BC

The logic diagram of Full Subtractor is Shown below



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