Output Select Analysis: By treating the invalid decimal values (10 through 15) as don't-care states, Karnaugh maps simplify the logic equations down to a streamlined structure. The highest bit D3 turns on only when both G3 and G2 are active.
Hardware Optimization: The circuit routes the Gray code inputs into a cascading network of gates. D2, D1, and D0 leverage shared XOR structures to decode the non-linear Gray transitions back into sequential binary values using the fewest possible parts.