Common-drain JFET stage naming: Is a JFET configured with its output taken from the source (common-drain) also known as a source follower?

Introduction / Context:Naming conventions in amplifier stages are consistent across FET types. In a common-drain configuration, the drain is AC-grounded (or held at a fixed potential), the input is applied at the gate, and the output is taken from the source. This topology is universally called a source follower because the output voltage closely follows the input, offset by a small source-gate bias-dependent amount.

Given Data / Assumptions:

• Three JFET terminals: gate, drain, source.
• Output sampled at the source node.
• Biasing ensures linear region operation for small signals.
• Load is connected to the source node (often via resistor).

Concept / Approach:The source follower provides high input impedance, low output impedance, and near-unity voltage gain (slightly less than 1). The stage does not invert the signal; hence “follower.” These properties make it valuable as a buffer between high-impedance sources and heavier loads, minimizing signal loss and distortion.

Step-by-Step Solution:

Verification / Alternative check:Compare with common-source (inverting gain) and common-gate (low input impedance, high bandwidth). Only the common-drain topology exhibits the follower behavior with high input and low output impedance.

Why Other Options Are Wrong:

Common Pitfalls:Expecting voltage gain > 1 from a follower; ignoring source resistor biasing’s effect on linearity; overlooking the follower’s finite output swing limits due to VGS headroom.

Final Answer:Correct