Full Subtractor | Definition | Circuit Diagram | Truth Table

Half Subtractor-

 

Before you go through this article, make sure that you have gone through the previous article on Half Subtractor.

 

We have discussed-

  • Half Subtractor is used for the purpose of subtracting two single bit numbers.
  • Half subtractors have no scope of taking into account “Borrow-in” from the previous circuit.
  • To overcome this drawback, full subtractor comes into play.

 

 

In this article, we will discuss about Full Subtractor.

 

Full Subtractor-

 

  • Full Subtractor is a combinational logic circuit.
  • It is used for the purpose of subtracting two single bit numbers.
  • It also takes into consideration borrow of the lower significant stage.
  • Thus, full subtractor has the ability to perform the subtraction of three bits.
  • Full subtractor contains 3 inputs and 2 outputs (Difference and Borrow) as shown-

 

 

Designing a Full Subtractor-

 

Full subtractor is designed in the following steps-

 

Step-01:

 

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

 

Step-02:

 

Draw the truth table-

 

Inputs
Outputs
ABBinBout (Borrow)D (Difference)
00000
00111
01011
01110
10001
10100
11000
11111

Truth Table

 

Step-03:

 

Draw K-maps using the above truth table and determine the simplified Boolean expressions-

 

 

Also Read- Full Adder

 

Step-04:

 

Draw the logic diagram.

The implementation of full adder using 1 XOR gate, 3 AND gates, 1 NOT gate and 1 OR gate is as shown below-

 

 

To gain better understanding about Full Subtractor,

Watch this Video Lecture

 

Next Article- Ripple Carry Adder

 

Get more notes and other study material of Digital Design.

Watch video lectures by visiting our YouTube channel LearnVidFun.

Summary
Article Name
Full Subtractor | Definition | Circuit Diagram | Truth Table
Description
Full Subtractor is a combinational logic circuit used for the purpose of subtracting two single bit numbers with a borrow. Full Subtractor Definition, Block Diagram, Truth Table, Circuit Diagram, Logic Diagram, Boolean Expression and Equation are discussed. Full Subtractor overcomes the limitation of Half Subtractor.
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Publisher Name
Gate Vidyalay
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