User`s guide

Control System Parts 6

-19

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 6-6 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

attributes:

NUM = 1

DENOM = 1 + .001*s

The gain and phase characteristics are shown in Figure 6-7.

ure 6-7

Lossy Integrator Example: Viewing Gain and

Phase Characteristics with Probe

This produces a PSpice A/D netlist declaration like this:

ERC 5 0 LAPLACE {V(10)} = {1/(1+.001*s)}

Example 2

The input is V(10). The output is a current applied between nets

5 and 0. The Laplace transform describes a lossy transmission

line. R, L, and C are the resistance, inductance, and capacitance

of the line per unit length.

ure 6-6

LAPLACE Part

Example 1

ure 6-8

LAPLACE Part

Example 2