Tag: 1 bit half adder

Half Adder

Half Adder-


  • Half Adder is a combinational logic circuit that is used for the purpose of adding two single bit numbers.
  • It contains 2 inputs and 2 outputs (sum and carry).



Designing a Half Adder-




Identify the input and output variables-

  • Input variables = A , B (either 0 or 1)
  • Output variables = S , C where S = Sum and C = Carry




Draw the truth table-

ABC (Carry)S (Sum)

Truth Table




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





Draw the logic diagram-


Logic Diagram


Here, Half Adder has been implemented using 1 XOR gate and 1 AND gate.


Limitation of Half Adder-


Half Adders have no scope of adding the carry bit resulting from the addition of previous bits.

This is a major drawback of half adders because real time scenarios involve adding the multiple number of bits which can not be accomplished using half adders.

To overcome this drawback, Full Adder comes into play.


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