# Chapter One

# INTRODUCTION

In this chapter, the basic concept of a switched capacitor performing as a simulated resistor is introduced. Some of the physical properties of switched-capacitor circuits are also briefly discussed. Then, a comparison is made between signal processors using switched-capacitor circuits and some alternative implementations, such as discrete analog circuits, digital filters, and analog bipolar integrated circuits. Finally, a few representative examples are given of circuits and systems utilizing MOS analog signal processing techniques, to illustrate the great potential of these circuits in telecommunication systems and related applications.

## 1.1. THE USE OF ANALOG MOS INTEGRATED CIRCUITS FOR SIGNAL PROCESSING.^{1} – ^{4}

Electrical signal processors are usually divided into two categories: analog and digital systems. An *analog system* carries signals in the form of voltages, currents, charges, and so on, which are *continuous* functions of the *continuous* time variable. Some typical examples of analog signal processors are audio amplifiers, passive- or active-RC filters, and so on. By contrast, in a *digital system* each signal is represented by a sequence of numbers. Since these numbers can only contain a finite number of digits (typically, coded in the form of binary digits or *bits*) they can only take on *discrete values*. Also, these numbers are the *sampled* values of ...