The most common equivalent circuit that is used for the FET amplifiers is the transconductance
amplifier, in which the input signal is a voltage and the output signal is a current.
Graphical Analysis, Load Lines, and Small-Signal Parameters
Figure 6. 1 shows an NMOS common-source circuit with a time-varying voltage source in series with
the dc source. We assume the time-varying input signal is sinusoidal. Figure 6.2 shows the transistor
characteristics, dc load line, and Q-point, where the dc load line and Q-point are functions of vGS,
VDD, RD and the transistor parameters.