Crossover distortion occurs in Class-B amplifiers.

Class-B amplifiers are commonly used in audio applications due to their efficiency and low power dissipation. However, they suffer from a type of distortion known as crossover distortion. This distortion occurs when the audio signal transitions from one half of the waveform to the other.

What is crossover distortion?

Crossover distortion is a type of distortion that occurs in amplifiers when there is a gap or overlap between the positive and negative half-cycles of the input waveform. It results in a distortion of the output waveform, causing harmonic distortion and affecting the overall audio quality.

How does crossover distortion occur in Class-B amplifiers?

Class-B amplifiers use a pair of complementary transistors (one NPN and one PNP) in a push-pull configuration. During the positive half-cycle of the input waveform, the NPN transistor conducts and amplifies the signal, while the PNP transistor remains off. Similarly, during the negative half-cycle, the PNP transistor conducts, and the NPN transistor is off. This push-pull configuration allows for efficient amplification.

However, there is a small gap or overlap between the conduction regions of the two transistors when the input signal crosses zero. This results in a region where neither transistor is conducting, causing a distortion in the output waveform. This gap or overlap is known as crossover distortion.

Effects of crossover distortion

Crossover distortion can have significant effects on the audio quality. It adds odd-order harmonics to the output signal, which can result in a harsh or distorted sound. Additionally, it can introduce non-linearities in the frequency response, affecting the accuracy and fidelity of the reproduced audio.

Methods to reduce crossover distortion

To reduce crossover distortion, several techniques can be employed in Class-B amplifiers:

1. Biasing: By introducing a small amount of bias current, the conduction regions of the transistors can be extended, reducing the crossover distortion.

2. Compensation circuits: These circuits use diodes or transistors to compensate for the voltage drop across the non-conducting transistors, effectively minimizing the crossover distortion.

3. Class-AB operation: Class-AB amplifiers operate in a region between Class-A and Class-B amplifiers. They incorporate a small amount of bias current to ensure that both transistors are conducting slightly, reducing the crossover distortion.

4. Feedback: Negative feedback can be used to compensate for the distortion introduced by crossover distortion, improving the linearity and reducing the overall distortion.

In conclusion, crossover distortion occurs in Class-B amplifiers due to the gap or overlap between the conduction regions of the push-pull transistors. This distortion can be reduced through various techniques such as biasing, compensation circuits, Class-AB operation, and feedback.