Simulating Class C RF Amplifiers

SPICE can be a versatile tool for RF work as long a few simple

precautions are taken. Significant parasitics must be included

in the circuit description, models of active devices must be

represented using subcircuits, and selection of transient analysis

options must be considered. The transient options include

the total analysis time, the data printout step and delay, and

the simulator error tolerances. Of course, SPICE will also do

AC analyses of RF circuits, but this is not its strong suite as

many other simulators will also do linear small signal work. The

real strength SPICE based simulators, such as ISSPICE3, is in

its time domain capability where either repetitive or nonrepetitive

waveforms can be used as stimulus. This ability is

handy for burst work, measurement of peak stresses under

normal operation or momentary fault conditions, detailed

study of bypass networks, and many other conditions. Since

test points do not load the circuit in any way, measurements

that would be impossible on the bench can be easily made with

the ISSPICE3 simulation.