OVERVIEW

One of the most important functions in signal processing is the conversion between analog and digital signals. In Section 1.1, the definition and distinction between analog and digital signals were presented. Figure 1.3-1 illustrated the typical block diagram of a signal-processing system. It was noted that there are areas where signal processing is done on analog signals and areas where the signal processing is done on digital signals. Consequently, it is necessary to be able to convert back and forth between the two types of signals. Therefore, analog-to-digital and digital-to-analog converters are an important part of any signal-processing system.

From the viewpoint of Table 1.1-2, analog-digital converters (ADCs) and digital-analog converters (DACs) are at the systems level. They typically contain one or more comparators, digital circuitry, switches, integrators, a sample-and-hold, and/or passive components. Another important component of the ADCs or DACs is a precise voltage reference. In this chapter, the voltage reference will not be discussed. However, methods of designing stable voltage references have been presented in Chapter 4. We will find that the op amp plays a major role in the DAC while the comparator is the important active component in the ADC. The DACs and ADCs presented here do not represent all possible approaches but have been selected to be compatible with CMOS technology.

The DAC is presented first because it is generally part of an ADC. Our presentation will introduce the DAC including its characterization and testing. Next, the various types of DACs will be examined...