The FET amplifier source follower circuit is another name for:

In a Field Effect Transistor (FET) "source follower" circuit, the input signal is applied to the gate and the output is taken from the source. Since the output voltage closely "follows" the input voltage, it gets this descriptive name. Because the input is at the gate and the output is at the source, the remaining terminal—the drain—is the terminal common to both the input and output loops. Therefore, the technical name for a source follower is a "common drain" circuit. Distractors like "common source" or "common gate" represent completely different configurations where the source or gate are the grounded or common elements respectively, rather than the drain.