Architectures for realizing analog-to-digital (A/D) converters can be roughly divided into three categories (Table 17.1)—low-to-medium speed, medium speed, and high speed. In this chapter, design details are discussed for these different approaches except for oversampling converters. Oversampling converters are best described using many signal processing concepts and are therefore discussed separately in Chapter 18.
Before proceeding, it should be noted that when discussing the design of A/D converters, we usually ignore the 0.5 LSB offset present in the A/D transfer characteristic. Such a simplification is made so as not to complicate the concepts presented. Many of the converter architectures described make extensive use of switched capacitor circuits and comparators; the reader is referred to those chapters for more detail on those circuits.
17.1 INTEGRATING CONVERTERS
Integrating A/D converters is a popular approach for realizing high-accuracy data conversion on very slow-moving signals. These types of converters have very low offset and gain errors in addition to being highly linear. A further advantage of integrating converters is the small amount of circuitry required in their implementation. One application that has traditionally made use of integrating converters is measurement instruments such as voltage or current meters.
A simplified diagram for a dual-slope integrating ...