PSpice User Guide

PSpice User Guide

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PSpice A/D User Guide Transient analysis October 2019 566 Product Version 17.4-2019 © 2022 All Rights Reserved. When selecting Fourier to run a harmonic decomposition analysis on a transient waveform, only a portion of the waveform is used. Using the Probe window in PSpice A/D, a Fast Fourier Transform (FFT) of the complete waveform can be calculated and its spectrum displayed. In the example shown in Figure 12-1 on page 559, the voltage waveform at node OUT2 from the transient analysis is used and the fundamental frequency is one megahertz for the harmonic decomposition. The period of fundamental frequency is one microsecond (inverse of the fundamental frequency). Only the last one microsecond of the transient analysis is used, and that portion is assumed to repeat indefinitely. Since V1's sine wave does indeed repeat every one microsecond, this is sufficient. In general, however, you must make sure that the fundamental Fourier period fits the waveform in the transient analysis.

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