Analog amplifiers: classification and generalization

Amplifiers with high open-loop gain (operational amplifiers) are frequently encountered in analog signal processing circuits, since the application of negative feedback enables numerous transfer functions to be implemented. The designer wanting to select an operational amplifier for a given application is met with a vast range of devices, with different architectures optimized for particular system requirements. This range seems to be ever expanding, with "novel" amplifier topologies offering enhanced performance over more conventional devices. This paper presents an overview of amplifier theory, and shows that many novel amplifier architectures are simply implementations of earlier theories which have been made possible by advances in process technology. The analysis also shows that many ideas such as fixed gain bandwidth product are not inherent to negative feedback amplifier circuits, but result from the choice of amplifier architecture within a particular application.