Question

Which of the following Amplifier produces least distortion in the output among all the power Amplifiers?

• A. Class-B
• B. Class-AB
• C. Class-C
• D. Class-A

Hint:

Remember: Higher Fidelity (Class A) = Lower Efficiency. Higher Efficiency (Class C) = Higher Distortion.

Answer 1

The Correct Option is D

Power amplifiers are classified based on their "conduction angle," which is the portion of the input signal cycle during which the output transistor is conducting current. 1. Class A Amplifiers: In a Class A amplifier, the output transistor conducts for the

full $360^\circ$ of the input cycle. The operating point (Q-point) is set exactly in the middle of the load line. Because the transistor is always "on" and operating in its linear region, the output waveform is a very faithful reproduction of the input, resulting in the least distortion.

2. Comparison with other classes:

• Class B: Conducts for only $180^\circ$. This causes significant "crossover distortion" where the signal crosses zero.

• Class AB: Conducts for slightly more than $180^\circ$ to reduce crossover distortion, but it still has more distortion than Class A.

• Class C: Conducts for much less than $180^\circ$. While highly efficient, it produces massive amounts of distortion and is mainly used for RF applications with tuned circuits.

3. The Trade-off: While Class A provides the highest fidelity (least distortion), it is the least efficient (max theoretical efficiency is 25% to 50%) because it draws full current even when no signal is present.