Crossover distortion

The term crossover signifies the "crossing over" of the signal between devices, in this case, from the upper transistor to the lower and vice versa.

Consider a positive-going swing: As long as the input is less than the required forward VBE drop (≈ 0.65 V) of the upper NPN transistor, it will remain off or conduct very little.

This kink is the most pronounced form of crossover distortion, and it becomes more evident and intrusive when the output voltage swing is reduced.

Other more subtle forms of crossover distortion, stemming from slight differences between the PNP and NPN devices, exist.

Most modern power amplifiers (including those used in hi-fi) employ both techniques, using both class-AB in their output stages, and feedback, offering reasonable efficiency and good distortion figures.