CARRY PROPAGATION AND THE LOOK-AHEAD CARRY CIRCUIT:
The carry propagate (Pi) and carry generate (Gi) variables are shown on the full adder logic circuit. The carries C1, C2, and C3 can be expressed in SOP form as functions of C0 and the different (Pi) and (Gi) as follows:
The logic diagram of the look-ahead generator is implemented in a two level form as shown in the following logic circuit.
The 4-bit adder with the carry look-ahead circuit is implemented as shown in the following circuit.