CMOS Amplifiers

Most CMOS amplifiers have identical bipolar counterparts and can therefore be analyzed in the same fashion. Our study in this chapter parallels the developments in Chapter 5, identifying both similarities and differences between CMOS and bipolar circuit topologies. It is recommended that the reader review Chapter 5, specifically, Section 5.1. We assume the reader is familiar with concepts such as I/O impedances, biasing, and dc and small-signal analysis. The outline of the chapter is shown below.



7.1.1   MOS Amplifier Topologies

Recall from Section 5.3 that the nine possible circuit topologies using a bipolar transistor in fact reduce to three useful configurations. The similarity of bipolar and MOS small-signal models (i.e., a voltage-controlled current source) suggests that the same must hold for MOS amplifiers. In other words, we expect three basic CMOS amplifiers: the “common-source” (CS) stage, the “common-gate” (CG) stage, and the “source follower.”

7.1.2   Biasing

Depending on the application, MOS circuits may incorporate biasing techniques that are quite different from those described in Chapter 5 for bipolar stages. Most of these techniques are beyond the scope of this book and some methods are studied in Chapter 5. Nonetheless, ...

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