SUBTRACTOR-HALF AND FULL SUBTRACTOR

Subtractor

          

The subtractor is used to subtract 2 binary digits.

The subtractor are of 2 types.They are:

                     1) Half subtractor

                     2) Full subtractor

1.Half Subtractor

• A combinational circuit which is used to subtract binary digits.
• Let us assume that the 2 inputs are A and B.
• The half subtractor will have 2 outputs.
• They are difference and borrow.
• Let us assume that the 2 outputs variables are ‘B for borrow’ and ‘D for difference’.
• The input output combination for half subtractor can be represented in the truth table is as shown below.

   

•     The circuit diagram for Half Subtractor is as shown below

• The Boolean function for difference and borrow can be derived from the truth table is as shown below.

                      D=A’B+AB

                      

                      B=A’B

2.Full Subtractor

• A combinational circuit which is used to perform the subtraction of 3 input variables.
• In full Subtractor there will be 3 inputs x, y, z and 2 outputs ‘D for difference’ and ‘B for borrow’.
• The input output combination for full Subtractor is represented in the truth table is as shown.

              

    The circuit diagram for Full Subtractor is as shown below

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