It is virtually impossible to find electronic devices in our daily lives that do not contain digital circuits. From watches and cameras to computers and cellphones, digital circuits account for more than 80% of the semiconductor market. Examples include microprocessors, memories, and digital signal processing ICs.
This chapter serves as an introduction to the analysis and design of digital CMOS (complementary metal oxide semiconductor) circuits. The objective is to provide a detailed transistor-level understanding of logical gates so as to prepare the reader for courses on digital circuit design. The outline is shown below.
In the past five decades, digital circuits have evolved dramatically, going from a few gates per chip in the 1960s to hundreds of millions of transistors per chip today. Very early generations incorporated only resistors and diodes and were called “resistor-diode logic” (RDL). These were followed by bipolar realizations such as “transistor-transistor logic” (TTL) and “emitter-coupled logic” (ECL). But it was the advent of CMOS technology and the unique properties of digital CMOS circuits that led to the explosive growth of digital systems. We will study and appreciate these properties in this chapter.