User Guide

Chapter 10 Transient analysis
268
Figure 67 Hysteresis curve example: Schmitt trigger.
Fourier components
Fourier analysis is enabled through the Output File
Options dialog box under the Time Domain (Transient)
Analysis type. Fourier analysis calculates the DC and
Fourier components of the result of a transient analysis.
By default, the first through ninth components are
computed; however, more can be specified.
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
Fast Fourier Transform (FFT) of the complete waveform
can be calculated and its spectrum displayed.
In the example shown in Figure 63 on page 10-263, the
voltage waveform at node OUT2 from the transient
analysis is to be used and the fundamental frequency is to
be 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
N
ote
Y
ou must
d
o a trans
i
ent ana
l
ys
i
s
in order to do a Fourier analysis. The
sampling interval used during the
Fourier transform is equal to the print
step specified for the transient analysis.
Pspug.book Page 268 Wednesday, November 11, 1998 1:14 PM