
Prefix Adder 79
2~6o4
2.7
Choice of Group Size and Number of Levels
As can be seen the group size and the number of levels affect both the delay and
the number of modules. A suitable choice depends on the technology and on
the adder requirements. With MSI technology, the size of the group was mainly
determined by the number of pins in a package. Moreover, the best size was the
maximum that could be included in a chip since this reduces the number of chips
as well as the number of signal hops between chips. On the other hand, with VLSI
technology, in which a whole adder fits in a chip, the constraints are different, and
simplicity ...