Common-collector (emitter follower) I/O terminals: In a CC stage, is the input applied to the base while the output is taken from the emitter?

Introduction / Context:The common-collector (CC) configuration, also known as the emitter follower, is widely used for buffering because it presents high input impedance and low output impedance with near-unity voltage gain. Correct terminal assignment is key to analyzing performance and biasing.

Given Data / Assumptions:

• Topology: base is the driven terminal; collector is at AC ground (often tied to the supply via decoupling); output is taken from the emitter.
• Operation in forward-active region.
• Small-signal analysis applies around the bias point.

Concept / Approach:In the emitter follower, the emitter voltage follows the base voltage minus V_BE. Because the collector is the common node for AC (hence “common-collector”), the stage does not invert and provides current gain, improving drive capability for loads without significant voltage amplification.

Step-by-Step Solution:

Verification / Alternative check:Measure gain: Av ≈ 0.9–0.99 depending on emitter load and transistor parameters; phase ≈ 0°.

Why Other Options Are Wrong:

Common Pitfalls:Forgetting voltage headroom (emitter must be below collector for NPN); overloading the emitter, which reduces gain and increases distortion.

Final Answer:Correct