1. A method for improving performance of noise analysis using a threshold based combination of noise estimation and simulation, comprising: classifying a circuit into one of four defined noise response groups based on the circuit's type; determining if an input noise of the classified circuit is small enough to skip simulation; estimating an output noise wave of the classified circuit; scaling down the estimated output noise wave by a scaling factor corresponding to the one of the four defined noise response groups of the classified circuit; and determining if the scaled down estimated output noise wave of the classified circuit is small enough to propagate or instead requires simulation, wherein at least one of the classifying, the estimating, and the scaling down are performed using a computer device including a processor.