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Sahithyan's S2
Sahithyan's S2 — Computer Organization And Digital Design

Adders

Half Adder

A digital circuit component that adds 2 bits. Outputs 2 bits: sum bit and carry bit.

Full Adder

A digital circuit component that adds 3 bits. Outputs 2 bits: sum bit and carry bit. An extension of the half adder where the carry bit of a half adder is input to another half adder. Built using 2 half adders.

Half   Adder Half   Adder Half   Adder Half   Adder A A C_in C_in C_out C_out S S A A B B A A S S S S B B B B C C C C

Ripple Carry Adder

Made by a chain of full adders joined as mentioned below:

Ripple Carry Adder

Image from Wikipedia.

Carry Lookahead Adder

A technique to speedup binary addition by calculating carry bits in parallel. In a CLA:

  • Carry generate - means C_out will be created
  • Carry propogate - means C_in will be sent out as C_out

Carry Lookahead Adder

The CLA can be used to create n-bit adders which only have 3 level delay.