3.1 Introduction

In this chapter we study basic switched-capacitor building blocks, which are the requisites for realizing analog sampled-data functions.

Switched-capacitor (SC) building blocks are often classified into two categories: passive and active. A passive SC building block (or element) is defined as a network composed of switches and capacitors only, whereas its active counterpart is not only built from switches and capacitors, but also active devices such as op-amps. Strictly speaking, a MOS switch is an active device, for it is composed of one or more transistors, which must be driven by the system clock or its derivatives. However, as we will see shortly, the primary use of SC-only elements is the simulation (or approximation) of the physical resistor; and in analog integrated circuits (ICs), the op-amp is usually regarded as the dividing line between passive and active integrated implementations. Therefore in this book we consider SC-only elements as passive and the others using op-amps as active.

As we have mentioned, the major application of passive SC elements is the physical resistor simulation in a monolithic configuration. Sometimes passive SC elements can also be used to construct passive filters and voltage converters. In comparison, as we will see in the following sections and chapters, active SC elements are widely adopted in the design of integrators, active filters, data converters, and so on.