Introduction to CMOS OP-AMPs and Comparators

CHAPTER 7

ANALOG-TO-DIGITAL CONVERTERS

The analog-to-digital converter (usually abbreviated ADC or A/D converter) is an essential building block in many digital signal-processing systems. It provides a link between the digital signal processor and the analog signals of a transducer. The A/D converter is considered to be an encoding device, where it converts an analog sample into a digital quantity with a prescribed number of bits. Numerous types of A/D converters have been designed for a wide variety of applications. The type of the application largely determines the choice of the A/D conversion technique. From the viewpoint of the implementation, analog-to-digital converters typically contain one or more comparators, switches, passive precision components, a precise voltage reference and digital control logic.

In this chapter the basic principles and performance metrics of the A/D converters are presented first. Following that, several types of Nyquist-rate A/D conversion techniques are examined, and their implementation in the CMOS technology is discussed.

7.1. ANALOG-TO-DIGITAL CONVERSION: BASIC PRINCIPLES

As was the case with Nyquist-rate digital-to-analog converters, there are a variety of algorithms and realizations available for analog-to-digital converters offering different advantages and disadvantages. The trade-offs between the conversion accuracy, speed, and economy (the latter measured by circuit complexity, chip area, power dissipation, etc.) offered by these options ...