Efficient simulation of harmonic distortion in discrete-time circuits

Espley showed in 1933 how to calculate harmonic distortion (HD) and inter-modulation distortion (IMD) using few equidistant points on the transfer characteristic of a circuit. This method was applied later to derive simplified formulae for HD in continuous-time amplifiers. It is shown in this paper that the main strength of the method lies in HD simulations in discrete-time amplifiers and filters. To show this, the theory is presented in a simple way and extended to distortion-induced offset. The precision for different HD levels is discussed for the first time in literature, showing that the method is precise to within 0.1 dB for distortions of -30 dB and below. Application examples are given to show that simulating with this method results in simulation times that are half as long as with the shortest possible (and barely practical) simulations using discrete Fourier transforms.