A common-base amplifier has a voltage gain that is

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Greater than one

Explanation: A common-base (CB) amplifier configuration provides a high voltage gain, typically much greater than one, despite having a current gain of less than unity. The voltage gain is primarily determined by the ratio of the output collector resistance to the small input emitter resistance.

Working Principle: In a CB amplifier, the input is applied to the emitter (low resistance) and the output is taken from the collector (high resistance). Since the current gain ($\alpha$) is nearly 1, the ratio of output resistance to input resistance ($R_c/r_e$) dominates the voltage gain, resulting in significant amplification of the voltage signal.

Key Formulas: $A_v = \frac{v_{out}}{v_{in}} \approx \frac{\alpha R_C}{r_e}$ — voltage gain calculation; $r_e \approx \frac{26mV}{I_E}$ — internal emitter dynamic resistance

Key Points: The current gain ($\alpha$) of a CB amplifier is always less than 1 (typically 0.95 to 0.99).; It offers low input impedance and high output impedance.; It is primarily used in high-frequency applications due to its excellent isolation between input and output.; The phase relationship between input and output signals is in-phase (0 degrees shift).

Advantages: High voltage gain; Low input impedance is ideal for matching low-impedance sources; Wide bandwidth compared to Common Emitter

Disadvantages: Low input impedance limits source loading; Current gain is less than unity; Requires impedance matching for multi-stage applications

Applications: High-frequency RF amplifiers; Impedance matching networks; Video frequency amplifiers

Additional Info: The common-base amplifier is often called a 'grounded-base' amplifier.. Option A is incorrect because the voltage gain is significantly large, not less than one.. Option B refers to the voltage follower (Common Collector), not the Common Base.

Answer: C is correct — The common-base amplifier configuration yields a voltage gain significantly greater than one due to the large ratio between output and input resistances.

Exam Tip: Remember: Common-Emitter has high voltage and current gain, Common-Collector has unity voltage gain (buffer), and Common-Base has high voltage gain but unity current gain.

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