GATE Papers >> CSE >> 2007 >> Question No 35

Question No. 35 CSE | GATE 2007

In a look-ahead carry generator, the carry generate function Gi and the carry propagate function Pi for inputs Ai and Bi are given by:

Pi=AiBi and Gi=AiBi

The expressions for the sum bit Si and the carry bit Ci+1 of the look-ahead carry adder are given by:

Si=PiCi and Ci+1=Gi+PiCi ,where C0 is the input carry

Consider a two-level logic implementation of the look-ahead carry generator. Assume that all Pi and Gi are available for the carry generator circuit and that the AND and OR gates can have any number of inputs. The number of AND gates and OR gates needed to implement the look-ahead carry generator for a 4-bit adder with S3, S2, S1, S0, and C4 as its outputs are respectively:


Answer : (C)   6, 4


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