User Guide

PSpice-equivalent parts
183
For AC analysis, the gain is found by substituting j·
ω for s.
This gives a flat response out to a corner frequency of
1000/(2π) = 159 Hz and a roll-off of 6 dB per octave after
159 Hz. There is also a phase shift centered around 159 Hz.
In other words, the gain has both a real and an imaginary
component. The gain and phase characteristic is the same
as that shown for the equivalent control system part
example using the LAPLACE part (see Figure 41 on
page 6-165).
For transient analysis, the output is the convolution of the
input waveform with the impulse response of
1/(1+.001·s). The impulse response is a decaying
exponential with a time constant of 1 millisecond. This
means that the output is the “lossy integral” of the input,
where the loss has a time constant of 1 millisecond.
This will produce a PSpice netlist declaration similar to:
ERC 5 0 LAPLACE {V(10)} = {1/(1+.001*s)}
Frequency response tables (EFREQ and GFREQ)
The EFREQ and GFREQ parts are described by a table of
frequency responses in either the magnitude/phase
domain or complex number domain. The entire table is
read in and converted to magnitude in dB and phase in
degrees. Interpolation is performed between entries.
Phase is interpolated linearly; magnitude is interpolated
logarithmically. For frequencies outside the table’s range,
0 (zero) magnitude is used.
EFREQ and GFREQ properties are defined as follows:
EXPR value used for table lookup; defaults
to V(%IN+, %IN-) if left blank.
TABLE series of either (input frequency,
magnitude, phase) triplets, or (input
frequency, real part, imaginary part)
triplets describing a complex value;
defaults to (0,0,0) (1Meg,-10,90) if left
blank.
Pspug.book Page 183 Wednesday, November 11, 1998 1:14 PM