An emitter follower has a voltage gain that is

Question

Examoogle · Accepted Answer

Approximately equal to one

Explanation: An emitter follower, also known as a Common Collector (CC) amplifier, acts as a voltage buffer where the output voltage at the emitter closely follows the input voltage applied at the base. Consequently, its voltage gain is slightly less than unity, typically ranging from 0.95 to 0.99.

Working Principle: In this configuration, the collector is common to both input and output circuits. The negative feedback inherent in the emitter resistor causes the output voltage to track the input voltage with a magnitude defined by $A_v = \frac{R_E || R_L}{r_e + (R_E || R_L)}$, where $R_E$ is the emitter resistor and $r_e$ is the dynamic emitter resistance. Since $R_E || R_L$ is much larger than $r_e$, the gain is approximately 1.

Key Formulas: $A_v = \frac{v_{out}}{v_{in}} \approx 1$; $Z_{in} = \beta(r_e + R_E)$

Key Points: High input impedance makes it ideal for impedance matching.; Low output impedance allows it to drive low-load resistances effectively.; The circuit provides current amplification but no voltage gain.; It is commonly used as a buffer stage in cascading amplifiers.

Advantages: High input impedance; Low output impedance; Wide bandwidth

Disadvantages: No voltage amplification; Vulnerable to high-frequency parasitic oscillations in some designs

Applications: Impedance matching buffer stages; Line drivers for signal transmission

Additional Info: The voltage gain is mathematically $A_v = \frac{R_E}{r_e + R_E}$, which is always less than 1.. Option C is incorrect because an emitter follower is not a voltage amplifier. Option D is incorrect as the gain is unity, not zero.

Answer: B is correct — An emitter follower provides a voltage gain of approximately one, functioning primarily as a unity-gain buffer.

Exam Tip: Always remember: Common Collector (Emitter Follower) = Voltage Buffer ($A_v \approx 1$); Common Base = Current Buffer ($A_i \approx 1$); Common Emitter = Voltage Amplifier ($A_v > 1$).

Related Questions

Discussion (0)