##### Carry Look Ahead Adder

In order to overcome the disadvantaged of Ripple carry Adder, we use carry look ahead Adder.

The problem with ripple carry adder is a dependency on the previous stage for carry bit.

**Note:** will be 1 if: is 1 and either of two input is 1 or Both inputs are 1

In other words, we can write is as

The reason we are using is: It gives output 1 when either of one input is 1

Step 1: Writing carry equation

let's assume

// generating term

// propagation term

Step 2: rewriting the carry equation in terms of and

Step 3: removing carry dependency

Now, we can clearly see that there is no carry dependency except

Final Picture:

Total number of AND gate used is: 10

Total number of OR gate used is: 4