User Guide

Control system parts
173
The last major component is an ABM expression
component to take an input voltage and convert it into a
current. The relevant ABM1/I part property looks like
this:
EXP1 = 200E-6 * V(%IN)
A final step in the model is to add device parasitics. For
example, a resistor can be used to give a finite output
impedance. Capacitances between the grid, cathode, and
anode are also needed. The lower part of the schematic in
Figure 47 shows a possible method for incorporating
these effects. To complete the example, one could add a
circuit which produces the family of I-V curves (shown in
Figure 48).
Figure 48 Triode subcircuit producing a family of I-V curves.
Pspug.book Page 173 Wednesday, November 11, 1998 1:14 PM