Design two versions of the combinational circuit whose input is a 4-bit number and whose output is the 2s complement of the input number, for each of the following cases using AND, OR and NOT gates:
(a) The circuit is a simplified two-level circuit, plus inverters as needed for the input variables.
(b) The circuit is made up of four identical two-input, two output cells, one for each bit. The cells are connected in cascade, with lines similar to a carry between them. The value applied to the rightmost carry bit is 1.

Question

Design two versions of the combinational circuit whose input is a 4-bit number and whose output is the 2s complement of the input number, for each of the following cases using AND, OR and NOT gates:
(a) The circuit is a simplified two-level circuit, plus inverters as needed for the input variables.
(b) The circuit is made up of four identical two-input, two output cells, one for each bit. The cells are connected in cascade, with lines similar to a carry between them. The value applied to the rightmost carry bit is 1.

anonymous · Answer

(c) Calculate the gate input costs for the designs in (a) and (b) and determine which is the better design in terms of gate input cost. Thanks!