Question

Class AB operation is often used in power amplifiers in order to

• A. Overcome a cross over distortion
• B. Decrease distortion
• C. Increase distortion
• D. Introduce non-linearity

Hint:

Class-B amplifiers are efficient but suffer from crossover distortion. Class-AB amplifiers provide a compromise between: \[ \text{Efficiency} \] and \[ \text{Low Distortion}. \]

Answer 1

The Correct Option is A

Concept: Power amplifiers are classified according to the conduction angle of the active device.
• Class A : \(360^\circ\)
• Class B : \(180^\circ\)
• Class AB : Between \(180^\circ\) and \(360^\circ\)
• Class C : Less than \(180^\circ\)

Step 1: Understand crossover distortion.
In a Class-B push-pull amplifier, one transistor conducts during the positive half-cycle while the other conducts during the negative half-cycle. Near the zero crossing point, neither transistor conducts perfectly. This produces a distortion called crossover distortion.

Step 2: Role of Class AB biasing.
In Class AB operation, each transistor is biased slightly above cutoff. As a result, both transistors conduct for a small interval around the zero crossing. This removes the dead zone responsible for crossover distortion.

Step 3: State the purpose of Class AB operation.
The main reason for using Class AB operation is \[ \boxed{\text{to overcome crossover distortion}} \] while maintaining good efficiency.