Carry Save AdderCME 433

Presented by:

Richard Aramenko

Luke Brisebois

Carry Save Adder

A digital adder

Used to sum 3 or more binary numbers

Outputs two numbers of equal dimensions as the input

This unique dual output consists of:

One sequence of partial sum bits

One sequence of carry bits

Application

The most important:

Calculating partial products in integer multiplication

Additional application includes:

Adding a large number of inputs together

Advantages and Disadvantages

Advantages:

Produces all of its outputs in parallel resulting in the same delay as a full adder

Very little propagation delay when implemented

Carry Save Adder plus a ripple adder = n+1

Two Ripple Carry adders = 2n

Allows for high clock speeds

Advantages and Disadvantages

Disadvantages

We do not know whether the result is positive or negative

This is a drawback when performing modular multiplication since you don’t know whether the intermediate result is greater or less than the modulus

Circuit Block

Example

The End