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 simpliied 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.

(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.