Contents 1. Introduction
The correct operation of analog circuits at low-voltage demands to explore new blocks and new circuits topologies. For analog circuits, the operational amplifier (opamp) is one of the most useful blocks. The opamp is usually made up of two gain stages, namely, the differential input stage and the output stage. In this paper,. we will place more emphasis on the output stage due to its high current, demanded by the resistive nature of the load. In class A output stages, the maximum current is equal to the bias current. Class B output stages combine high output current capability with very low quiescent current but introduce crossover distortion. The common-source class AB stage, Fig. 1(a), presents a good trade-off between distortion and quiescent dissipation. The output transistors are biased with a small quiescent current compared to the maximum output current, which reduces crossover distortion in comparison with class B output stage. Furthermore, a minimum current in the output transistors, for any bias condition, prevents a turn-on delay of the non-active transistor and, thus, crossover distortion [6].
