AXL amplifier - class A, B or AB

The classification of an amplifier depends on the portion of the input current cycle during which output current flows. In class A amplifiers, output current flows over the whole of the input current cycle. These amplifiers have low distortion and low efficiency. In class B amplifiers the output current is cut off at zero input signal, so that a half-wave rectified output is produced. Such amplifiers are very effi- cient but suffer from cross-over distortion. In class AB amplifiers the output current flows for more than half but less than the whole of the input cycle. At low input- signal levels class AB amplifiers tend to operate in class A, and at high input- signal levels as class B amplifiers. Power amplifiers commonly work in push- pull, that is, they use two matched devices in such a way that they operate with a 180° phase difference. The output circuits combine the separate outputs in phase. When complementary transistors are used in the two halves, no phase shift is requi...