n Bit Parallel Adder:
We have seen, a single full-adder is capable of adding two one-bit numbers and an input carry. In order to add binary numbers with more than one bit, additional full-adders must be employed. A n Bit Parallel Adder can be constructed using number of full adder circuits connected in parallel.
Block Diagram of n Bit Parallel Adder:
Fig. 3.25 shows the block diagram of n Bit Parallel Adder using number of full-adder circuits connected in cascade, i.e. the carry output of each adder is connected to the carry input of the next higher-order adder.
It should be noted that either a half-adder can be used for the least significant position or the carry input of full adder is made 0 because there is no carry into the least significant bit position.
Design of 4 Bit Parallel Adder using Full Adder:
Fig. 3.26 shows the block diagram of 4-bit parallel adder and Fig. 3.27 shows logic diagram for 4 bit parallel adder. Here, for least significant position, carry input of full adder is cascade 0.