PSpice User Guide
Analog behavioral modeling
October 2019 371 Product Version 17.4-2019
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Here are some guidelines:
■ In the case of a Laplace device (ELAPLACE), multiply the
Laplace expression by e to the
(-s ∗ ).
■ In the case of a frequency table (EFREQ or GFREQ), do either
of the following:
❑ Specify the table with
DELAY=.
❑ Compute the delay by adding a phase shift.
Chebyshev filters
All of the considerations given above for Laplace parts also apply to
Chebyshev filter parts. However, PSpice A/D also attempts to deal
directly with inaccuracies due to sampling by applying Nyquist criteria
based on the highest filter cutoff frequency. This is done by checking
the value of TMAX. If TMAX is not specified it is assigned a value, or
if it is specified, it may be reduced.
For low pass and band pass filters, TMAX is set to (0.5/FS), where
FS is the stop band cutoff in the case of a low pass filter, or the upper
stop band cutoff in the case of a band pass filter.
For high pass and band reject filters, there is no clear way to apply
the Nyquist criterion directly, so an additional factor of two is thrown
in as a safety margin. Thus, TMAX is set to (0.25/FP), where FP is
the pass band cutoff for the high pass case or the upper pass band
cutoff for the band reject case. It may be necessary to set TMAX to
something smaller if the filter input has significant frequency content
above these limits.
Frequency tables
For frequency response tables, the maximum frequency is twice the
highest value. It will be reduced to 10/(RELTOL⋅TSTOP) or 8192
times the frequency resolution if either value is smaller.
The frequency resolution for frequency response tables is taken to be
either the smallest frequency increment in the table or the fastest rate
