Draw the gate-level schematic to compute the group -generate signal and the grou

Question

Draw the gate-level schematic to compute the group -generate signal and the group-propagate signalof a 4-bit block using 2-input gates and one 4-input gate. The inputs to this circuit should be the 4-bit operands and the output should be the group-generate and group-propagate signals. Lets call this generate-propagate circuit.

Draw the black-box model for the generate-propagate circuit. Label inputs and outputs inside the block diagram and specify bus sizes for all inputs and outputs. Call this GP.

Draw the look-ahead logic circuit to compute the output carry of a 4-bit block from the group- generate, group-propagate and input carry.

Explanation / Answer

genrate and propagate ckt:

The carry-look-ahead adder solves this problem by calculating the carry signals in advance, based on the input signals. It is based on the fact that a carry signal will be generated in two cases: (1) when both bits Ai and Bi are 1, or (2) when one of the two bits is 1 and the carry-in (carry of the previous stage) is 1. Thus, one can write,

COUT = Ci+1 = Ai.Bi + (Ai

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