SYSTEMS APPROACH- EFFECTS OF RS AND RL

TWO-PORT SYSTEMS
The description to follow can be applied to any two-port system—not only those containing
BJTs and FETs—although the emphasis in this chapter is on these active devices.
The emphasis in previous chapters on determining the two-port parameters for
various configurations will be quite helpful in the analysis to follow. In fact, many of
the results obtained in the last two chapters are utilized in the analysis to follow.
In Fig. 10.1, the important parameters of a two-port system have been identified.
Note in particular the absence of a load and a source resistance. The impact of these
important elements is considered in detail in a later section. For the moment recognize
that the impedance levels and the gains of Fig. 10.1 are determined for no-load
(absence of RL) and no-source resistance (Rs) conditions.
If we take a “Thévenin look” at the output terminals we find with Vi set to zero
that
ZTh Zo Ro