OVERVIEW

From the viewpoint of Table 1.1-2, the previous two chapters have provided the background for understanding the technology and modeling of CMOS devices and components compatible with the CMOS process. The next step toward our objective methodically developing the subject of CMOS analog circuit design is to develop subcircuits. These simple circuits consist of one or more transistors and generally perform only one function. A subcircuit is typically combined with other simple circuits to generate a more complex circuit function. Consequently, the circuits of this and the next chapter can be considered as building blocks.

The operational amplifier, or op amp, to be covered in Chapters 6 and 7, is a good example of how simple circuits are combined to perform a complex function. Figure 4.0-1 presents a hierarchy showing how an operational amplifier a complex circuit might be related to various simple circuits. Working our way backward, we note that one of the stages of an op amp is the differential amplifier. The differential amplifier consists of simple circuits that might include a current sink, a current-mirror load, and a source-coupled pair. Another stage of the op amp is a second gain stage, which might consist of an inverter and a current-sink load. If the op amp is to be able to drive a low-impedance load, an output stage is necessary. The output stage might consist of a source follower and a current-sink load. It is also necessary to provide a stabilized bias for each of the previous stages. The biasing...