Combination Circuits

     In digital circuit theory, we use combination circuits to  implement Boolean Circuits. In this kind of circuits, OUTPUT is always depends on CURRENT INPUT. 

     Here is the example block diagram for combination circuit,

     We can separate combination circuit into two simple Arithmetic circuits,

1. Half Adder
2. Full Adder

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 Half Adder

    Normally, a unit which add two input variables called adder. In Half adder, it has only two inputs. It will add two single binary digits(ex- A and B). It has two outputs, SUM(s) and CARRY(c). Normally we use XOR gate for SUM and AND gate for CARRY.

     Hence the main purpose of the Half Adder is, add two input bits and generate SUM and CARRY. 

A	B	sum	carry
0	0	0	0
0	1	1	0
1	0	1	0
1	1	0	1

SUM      = A XOR B

CARRY = A AND B

     Here is the Block Diagram of Half Adder,

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Full Adder

    This kind of adders have 3 inputs. Hence it can give arithmetic sum of three input bits. The main different between of Half Adder and Full Adder is, Full Adder has "Carried In"(Cin) as well as "Carried Out"(Cout). Hence Full Adder has A, B, Cin INPUTS. A and B are the operands and Cin is a bit carried in from the previous less-significant stage. 

 Here is the Block Diagram of FULL ADDER