Digital Arithmetic

Variable-Time Adder 91

Y3 x3 Y2 x2

I

I FA

I Latch

FA

Yl Xl Yo Xo

FA

--I--

FA

S 3 S 2 S 1 S O

FIGURE 2.20

Pipelined carry-ripple adder (for group size of 1 and n - 4).

C O

2 = 9

l~

Pipelined Adders

The throughput of the adder can be increased by pipelining. To do this, pipeline

registers are introduced to shorten the worst-case carry path. For example, a

C RA adder is divided into groups of bits and latches are introduced, as shown

in Figure

2.26.

Most latches are used to synchronize inputs and outputs since

different parts (groups) are processed at different cycles. The throughput R is

determined by the ...