An

electronic device made for the

addition of two (or more, I suppose)

binary numbers. It is generally constructed of

half and

full adders, with the

carry out of each adder connected to the

carry in of the

next most significant adder.

This is a fairly fast method of addition, but as you add more and more adders to the ripple adder, it begins to slow down, because any change to an input has to "ripple" through **all** the carry ins/carry outs of each adder. See carry lookahead adder for one way to combat this.

An example 4 bit ripple adder that does the addition S=A+B:

S3 S2 S1 S0
| | | |
| | | |
+---+----+ +---+----+ +---+----+ +---+----+
| Sum | | Sum | | Sum | | Sum |
| | | | | | | |
Cout--|Cout Cin|--|Cout Cin|--|Cout Cin|--|Cout |
| | | | | | | |
| FA | | FA | | FA | | HA |
| | | | | | | |
| A B | | A B | | A B | | A B |
+-+---+--+ +-+---+--+ +-+---+--+ +-+---+--+
| | | | | | | |
| | | | | | | |
A3 B3 A2 B2 A1 B1 A0 B0