Output Resistance
the output resistance is defined as the évenin resistance at the output of the amplifier looking back into the amplifier. As in the case of the simple common-source amplifier, Ro is measured without considering RD.
Calculations to determine the output resistance of the common-source amplifier with
source resistor are based on the small-signal model of Figure 5.31b and is similar to the calculations performed previously for the common-source amplifier without source resistor. e circuit of Figure 5.33 defines the necessary topology and circuit variables for output resistance calculations.