Emitter Follower Amplifier Configuration Details

The question asks to identify the specific Bipolar Junction Transistor (BJT) amplifier configuration that acts as an Emitter Follower.

Understanding Amplifier Configurations

BJT amplifiers are typically categorized into three basic configurations based on which terminal is common to both the input and output signals:

• Common Base (CB): The base terminal is common. The input signal is applied to the emitter, and the output is taken from the collector. This configuration offers high voltage gain ($A_v$) and low current gain ($A_i$). It's often used for impedance matching.
• Common Emitter (CE): The emitter terminal is common. The input signal is applied to the base, and the output is taken from the collector. This configuration provides both high voltage gain ($A_v$) and current gain ($A_i$), but it introduces a 180-degree phase shift between the input and output signals.
• Common Collector (CC): The collector terminal is common. The input signal is applied to the base, and the output is taken from the emitter. This configuration is also known as the Emitter Follower because the output voltage at the emitter closely follows the input voltage at the base.

The Emitter Follower Explained

An Emitter Follower configuration is characterized by:

• Voltage Gain ($A_v$): Approximately equal to 1 (unity gain). $A_v \approx 1$.
• Current Gain ($A_i$): High, similar to the common emitter configuration.
• Input Impedance ($Z_{in}$): High.
• Output Impedance ($Z_{out}$): Low.

Due to its high input impedance and low output impedance, the emitter follower configuration is excellent for impedance matching and buffering applications, preventing loading effects on the preceding stage.

Identifying the Correct Configuration

The name "Emitter Follower" directly arises from the behavior of the output signal at the emitter terminal. In the Common Collector configuration, the output is taken from the emitter, and its voltage variation closely mirrors the input voltage variation at the base. This characteristic makes the Common Collector the correct configuration for an emitter follower amplifier.

Therefore, the configuration used for an Emitter follower Amplifier is the Common Collector.