Abstract: The present invention includes a method for generating a model of a circuit having an input port and an output port. The method determines an amplitude for current leaving the output port at a frequency ?k when a signal that includes a carrier at ?j modulated by a signal Vj(t) is input to the input port, wherein ?k is a harmonic of ?j. The determined amplitude is used to determine values for a set of constants, ak, such that a function fk(V,ak) provides an estimate of the current, Ik(t), leaving the output port at a frequency ?k when a signal having the form V ? ( t ) = Re ? ? k = 1 , H ? V k ? ( t ) ? exp ? ( j? k ? t ) is input to the input port. Here Vk(t) is a component of a set of values V. The fk(V,ak) are used to provide a simulator component adapted for use in a circuit simulator.