
Basic Carry-Ripple Adder (CRA) and FA Implementation
59
2~
Now, the sum bit is
S13 =X13 ~)Y13 ~)'5'13 = 0
Basic Carry-Ripple Adder (CRA) and FA
Implementation
We review here the carry-ripple adder, which corresponds to the basic (carry-
propagate) addition algorithm. As shown in Figure 2.4, this adder consists of
an array of 1-bit adders
(full-adders
or FAs) defined by expressions (2.4). The
correctness of this adder implementation can be shown by induction, using the
definition
ofci
given by expression (2.6).
Consider now the delay of the addition. Since there is no completion signal,
it is necessary to consider the worst-case ...