Crossoverforvrængning

Crossoverforvrængning, also known as crossover distortion or simply crossover, is a type of signal distortion that occurs in electronic amplifier circuits, particularly those employing complementary symmetry output stages. This distortion happens when the amplifier transitions from amplifying a positive-going signal to a negative-going signal, or vice-versa. Specifically, it arises from the fact that semiconductor devices, such as transistors, have a "dead zone" or quiescent current leakage around the zero-crossing point of the signal. During this brief period, neither the positive-going amplifying device (e.g., NPN transistor) nor the negative-going amplifying device (e.g., PNP transistor) is fully conducting, leading to a loss of signal integrity.

The audible effect of crossover distortion is a harsh, grainy, or buzzing sound, especially noticeable at low volumes or during quiet passages in music. It is more prevalent in Class B amplifier designs, where the output transistors are biased just below conduction to minimize quiescent current. Class AB amplifiers, which introduce a small quiescent current to keep both transistors slightly conductive, significantly reduce crossover distortion. Techniques to mitigate this distortion include proper biasing of the output stage, using devices with faster switching times, or employing negative feedback. While it was a common issue in early solid-state amplifiers, modern amplifier designs often employ sophisticated methods to eliminate it to a negligible level.