This paper presents a method to minimize the total energy consumption under time and area constraints, considering interconnection and functional unit energy. Multiple supply and threshold voltage scheme is used to minimize the static and dynamic energy in the functional units. A genetic algorithm based search method is proposed for the energy consumption minimization problem, so that near-optimal solution can be found in a reasonable time for large-size problems. Interconnection simplification is achieved by increasing the sharing of interconnections among functional units. Experimental results show that up to 30% of energy savings can be achieved by our proposed method.