User Guide

Control system parts
165
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. 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. The LAPLACE part shown in Figure 40
could be used for this purpose.
The transfer function is the Laplace transform
(1/[1+.001*s]). This LAPLACE part is characterized by the
following properties:
NUM = 1
DENOM = 1 + .001*s
The gain and phase characteristics are shown in Figure 41.
Figure 41 Viewing gain and phase characteristics of a lossy
integrator.
This produces a PSpice netlist declaration like this:
ERC 5 0 LAPLACE {V(10)} = {1/(1+.001*s)}
Example two
The input is V(10). The output is a current applied
between nets 5 and 0. The Laplace transform describes a
Figure 40 LAPLACE part example one.
Figure 42 LAPLACE part example two.
Pspug.book Page 165 Wednesday, November 11, 1998 1:14 PM