An Full Adder has both a carry-on and a carryout and Half Adder Doesn’t have a carry-in. A half adder can be used to add the least significant digit of a binary number or two binary digits alone.
Full Adders can be chained together to add a multi-bit number; An n bit parallel adder, there must be an N number of full adder circuits.
What is a parallel adder?
The parallel adder is a combinatorial circuit (not clocked, does not have any memory and feedback) adding every bit position of the operands at the same time.
Thus it is requiring a number of bit-adders(full adders + 1 half adder) equal to the number of bits to be added
What is Full Adder?
The adder outputs two numbers, a sum and a carry bit. The term is contrasted with a half adder, which adds two binary digits.
What is Half Adder?
A half adder is a type of adder, an electronic circuit that performs the addition of numbers. The half adder is able to add two single binary digits and provide the output plus a carrying value.
It has two inputs, called A and B, and two outputs S (sum) and C (carry). The common representation uses an XOR logic gate and an AND logic gate.