Design optimization methodologies for AMS-SoCs with analog, digital, and mixed-signal portions have not received significant attention, due to the increased complexity. In the mixed-signal circuits design, optimization and simulation are still important issues as they make the design cycle longer. This paper presents a new approach to reduce design optimization time. The approach relies on the fact that optimization carried out over a metamodel (which is an abstracted representation of the circuit model) instead of the actual circuit will allow fast design space exploration and reduce the design cycle time. In this paper three different optimization algorithms are compared: exhaustive search, tabu search and simulated annealing algorithms are analyzed to determine their suitability for metamodeling-based optimization. A ring oscillator is designed for a 45 nm nano-CMOS technology and the post-layout parasitic netlist is used as a test case for a comparative study. It is observed that the metamodel-based simulated-annealing optimization algorithm achieved ~9000X speed-up over the actual circuit-based optimization.