Patent ID: 7778315

Claim:
A method of measuring instantaneous signal dependent nonlinear distortion in a system under test comprising the steps of: applying a narrow time window to an output signal from the system under test to produce time windowed data that represents a portion of the output signal that contains a frequency of interest, the output signal being generated in response to a test signal having a varying frequency sinusoidal component and the time windowing being centered at a specified time within a corresponding varying frequency sinusoidal component of the output signal; measuring magnitudes of spectral peaks generated from the time windowed data, wherein the spectral peaks correspond to a nominal frequency and distortion frequencies for the time windowed data; and determining from the magnitudes of the spectral peaks a measure of the instantaneous signal dependent nonlinear distortion, the measure of the instantaneous signal dependent nonlinear distortion being a ratio of a square root of a sum of the squares of the magnitudes of the spectral peaks for the distortion frequencies to the magnitude of the spectral peak for the frequency of interest.