Determination of nonlinearity from its harmonic response

A simple method is given for determining the equation of an instantaneous single-valued nonlinear characteristic from measurement of the magnitude of its output harmonics in response to a sinusoidal input. The method, which relies on the orthogonality of the Cheby¿shev polynomials, gives the nonlinear characteristic as a power series in these polynomials, with the normalised input magnitude as argument. If desired, this can easily be written in terms of powers of the input.