TABLE OF CONTENTS The CMOS IC-fabrication technology has evolved as a practical choice for the implementation of low-power, relatively fast, signal-processing devices. The process is efficient, reliable, and low cost, while providing a high density of transistor-like components. A drawback to the process is that the fabrication of resistors uses large amounts of area, and so, the switched capacitor concept was developed to virtually eliminate the requirement for resistors in the fabrication of active filter components.
The purpose of this chapter is to introduce the switched capacitor equivalent of resistance concept and to show how this technology can be used to implement complex filter designs on a chip. This chapter does not go into the theory of the design or operation of CMOS devices. The student is referred to their basic electronics course textbooks or notes. A review of CMOS design concepts is presented in [1].
The circuit shown in Figure 7.1 illustrates the conceptual design for a CMOS switch. It is often referred to as a transmission gate, and it allows current to flow in either direction. This action is modeled with a simpler schematic as shown in Figure 7.2. This latter schematic just indicates the voltage controlled action of the switch; however, inspection of Figure 7.1 can provide some limitations on the range and values of the gate voltage, V gate, in order to obtain proper switch action.
