Crossover distortion behavior is characteristic of
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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.
Step 1: Define Crossover Distortion.
Crossover distortion is a type of distortion that occurs in push-pull amplifiers. It is the distortion that happens during the transition, or "crossover," when one transistor in the push-pull pair turns off and the other turns on.
Step 2: Analyze Class B Amplifier operation.
A Class B amplifier uses two complementary transistors (e.g., NPN and PNP) where each transistor conducts for only one-half (180 degrees) of the input signal cycle. For a silicon BJT, a base-emitter voltage of about 0.7V is required for the transistor to start conducting.
Step 3: Identify the cause of distortion.
When the input signal is near zero volts (crossing over from positive to negative or vice-versa), neither transistor is conducting because the input voltage is insufficient (less than 0.7V) to turn either one on. This creates a "dead zone" in the output signal around the zero-crossing point, which is known as crossover distortion. Class AB amplifiers are designed specifically to eliminate this by providing a small quiescent bias current that keeps both transistors slightly on even with no signal.
