A full adder circuit is an arithmetic circuit block that can be used to add three bits to produce a
SUM and a CARRY output. Such a building block becomes a necessity when it comes to adding
binary numbers with a large number of bits. The full adder circuit overcomes the limitation of the
half-adder, which can be used to add two bits only. Let us recall the procedure for adding larger
binary numbers. We begin with the addition of LSBs of the two numbers. We record the sum under
the LSB column and take the carry, if any, forward to the next higher column bits. As a result,
when we add the next adjacent higher column bits, we would be required to add three bits if there
were a carry from the previous addition. We have a similar situation for the other higher column bits also until we reach the MSB. A full adder is therefore essential for the hardware implementation of an adder circuit capable of adding larger binary numbers. A half-adder can be used for addition of LSBs only.
SUM and a CARRY output. Such a building block becomes a necessity when it comes to adding
binary numbers with a large number of bits. The full adder circuit overcomes the limitation of the
half-adder, which can be used to add two bits only. Let us recall the procedure for adding larger
binary numbers. We begin with the addition of LSBs of the two numbers. We record the sum under
the LSB column and take the carry, if any, forward to the next higher column bits. As a result,
when we add the next adjacent higher column bits, we would be required to add three bits if there
were a carry from the previous addition. We have a similar situation for the other higher column bits also until we reach the MSB. A full adder is therefore essential for the hardware implementation of an adder circuit capable of adding larger binary numbers. A half-adder can be used for addition of LSBs only.
