Possible Solutions
In the case of a class B/AB amplifier, crossover distortion can be reduced by using a slight forward bias in the base circuit such that the transistors are idling at a small output current. The forward bias causes the circuit to operate in class-AB mode, so both transistors are slightly on during crossover. This can reduce or eliminate the characteristic kink of crossover distortion, although other types of crossover distortion will remain.
As with most kinds of distortion, another way in which crossover distortion can be reduced is through the use of feedback. By comparing the output to the desired output, and adjusting the input to correct for any error, we can significantly reduce distortion. This may be done with an operational amplifier, as shown below, or with a discrete circuit.
In the example shown, the operational amplifier is used to reduce the distortion of a push-pull pair. Op-amps are differential voltage amplifiers with very high gain (sometimes modeled as infinite gain). In an ideal model, the output of the op amp is held such that both inputs of the op amp must be at exactly the same voltage. In this case, since the inverting input is directly connected to the output, the voltage at the non-inverting input is always equal to the voltage at the output and inverting input, hence eliminating distortion. With a more precise model of an operational amplifier (with non-infinite gain) distortion is reduced by a factor equal to the gain of the op amp.
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.
See also: Electronic amplifierRead more about this topic: Crossover Distortion
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