Question

Crossover distortion behavior is characteristic of

• A. Class A amplifier.
• B. Class B amplifier.
• C. Class AB amplifier.
• D. Common-base amplifier.

Hint:

Remember the amplifier classes and their key characteristics: - \textbf{Class A:} Always on, no crossover distortion, but inefficient. - \textbf{Class B:} Each half is on for 180°, efficient but suffers from crossover distortion. - \textbf{Class AB:} A compromise that biases transistors to be slightly on, eliminating crossover distortion while maintaining good efficiency.

Answer 1

The Correct Option is B

Step 1: Crossover distortion defined.Crossover distortion is a form of signal degradation found in push-pull amplifiers. It arises during the switching phase, or "crossover," as one transistor shuts off and the other activates in the push-pull configuration.
Step 2: Class B Amplifier operation analyzed.A Class B amplifier employs two complementary transistors (such as NPN and PNP types). Each transistor conducts for only half (180 degrees) of the input signal's cycle. Silicon BJTs require approximately 0.7V of base-emitter voltage to initiate conduction.
Step 3: Distortion cause identified.When the input signal approaches zero volts (transitioning between positive and negative), neither transistor conducts because the voltage is inadequate (below 0.7V) to activate either. This results in a "dead zone" in the output signal around the zero-crossing point, termed crossover distortion. Class AB amplifiers are designed to mitigate this by applying a small quiescent bias current, ensuring both transistors remain slightly active even without an input signal.