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 signal

of 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.

Draw the black-box diagram for the look-ahead logic with the inputs and the outputs appropriately labeled. Call this block LA.

Use the RCA, GP, and the LA block to create one level of the CLA.

Draw the black-box model of the circuit designed in step 9. Clearly label inputs and outputs inside the

box. Call this CLA_Level.

Put together 8 CLA_Level blocks to produce a 32-bit CLA.

Explanation / Answer

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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