- Full Subtractor is a combinational logic circuit that is used for the purpose of subtracting two single bit numbers taking into consideration borrow of the lower significant stage.
- Thus, Full Subtractor has the ability to perform the subtraction of three bits unlike half subtractor which can subtract only two bits.
- It contains 3 inputs and 2 outputs (Difference and Borrow).
Designing a Full Subtractor-
Identify the input and output variables-
- Input variables = A , B , Bin (either 0 or 1)
- Output variables = D , Bout where D = Difference and Bout = Borrow
Draw the truth table-
|A||B||Bin||Bout (Borrow)||D (Difference)|
Draw the K-maps using the above truth table and determine the simplified Boolean expressions-
Draw the logic diagram-
Here, Full Subtractor has been implemented using 1 XOR gate, 3 AND gates and 1 OR gate.
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