ADDERS are generally of five types:

1) Ripple Carry Adder: The Ripple carry adder(RCA) consists of a building block named Half Adder(HA) which is cascaded to form a Full Adder(FA). These building blocks HAs and FAs are also the building blocks of all types of adders.The N full adders are cascaded to form n bit RCA.

The full adder has three input PINS(input Ai,input Bi,carryin Ci) and two output pins(Sum and Ci+1).Its equations are:

Sum=Ai^Bi^Ci

Ci+1=Ai.Bi+Bi.Ci+Ai.Ci

2)Carry Lookahead Adder: The Carry Lookahead Adder(CLA) reduces the delay as that in RCA. Let

Gi=Ai.Bi, and Pi=Ai^Bi, then Ci+1=Gi+Pi.Ci.

The expressions for Sum and Ci+1 is then defined completely in terms of input pins rather WAIT for input carry to appear.

3)Carry Select Adder: The carry select adder uses duplicate modules for each combination of input carry(i.e. 1 and 0).The multiplexers then select the APPROPRIATE sum and carry output according to the carry output of the preceding stages.

Adders are generally of five types:

1) Ripple Carry Adder: The Ripple carry adder(RCA) consists of a building block named Half Adder(HA) which is cascaded to form a Full Adder(FA). These building blocks HAs and FAs are also the building blocks of all types of adders.The n full adders are cascaded to form n bit RCA.

The full adder has three input pins(input Ai,input Bi,carryin Ci) and two output pins(Sum and Ci+1).Its equations are:

Sum=Ai^Bi^Ci

Ci+1=Ai.Bi+Bi.Ci+Ai.Ci

2)Carry Lookahead Adder: The Carry Lookahead Adder(CLA) reduces the delay as that in RCA. Let

Gi=Ai.Bi, and Pi=Ai^Bi, then Ci+1=Gi+Pi.Ci.

The expressions for Sum and Ci+1 is then defined completely in terms of input pins rather wait for input carry to appear.

3)Carry Select Adder: The carry select adder uses duplicate modules for each combination of input carry(i.e. 1 and 0).The multiplexers then select the appropriate sum and carry output according to the carry output of the preceding stages.