1.1 The Role and Place of Modern Mixed Analog-Digital Chips

This is a book about devices and technology for mixed analog-digital chips. We will not use the common term mixed-signal to characterize such chips, in order to avoid the connotation of ambiguity that this term has in figurative speech; also, this term does not make explicit what kinds of signals are mixed and is often used in a sense that is not broad enough. Thus, we will stick to mixed analog-digital, and, for brevity, we will be talking of MAD chips. Such chips can be made by using very large-scale integration (VLSI) technologies, and they can contain over 1 million transistors and other devices.

In the early 1970s, it was already clear that the pervasiveness of the digital computer had begun. To some, this observation meant that the role of analog circuits would diminish, and in fact the decline of analog circuits was forecast in technical journals, trade magazines, and even the popular press. Such predictions never materialized. What happened instead was that the pervasiveness of the digital computer became a key factor for the increased pervasiveness of analog, and eventually MAD, circuits. There are two main reasons for this, and both are discussed below.

1. The need to interface the computer to the analog world. Digital computers do not operate in a vacuum; as they pervade our physical, analog world, they must interface with it. In most instances where a new application for the computer is...